Untangling the mechanics of knots

The researchers carried out experiments to test how much force is required to tighten knots with an increasing number of twists. They then compared their observations with their theoretical predictions, and found that the theory accurately predicted the force needed to close a knot, given its topology and the diameter and stiffness of the underlying strand. Credit: © highwaystarz / Fotolia
The researchers carried out experiments to test how much force is required to tighten knots with an increasing number of twists. They then compared their observations with their theoretical predictions, and found that the theory accurately predicted the force needed to close a knot, given its topology and the diameter and stiffness of the underlying strand.
Credit: © highwaystarz / Fotolia

Got rope? Then try this experiment: Cross both ends, left over right, then bring the left end under and out, as if tying a pair of shoelaces. If you repeat this sequence, you get what’s called a “granny” knot. If, instead, you cross both ends again, this time right over left, you’ve created a sturdier “reef” knot.

The configuration, or “topology,” of a knot determines its stiffness. For example, a granny knot is much easier to undo, as its configuration of twists creates weaker forces within the knot, compared with a reef knot. For centuries, sailors have observed such distinctions, choosing certain knots over others to secure vessels — largely by intuition and tradition.

Now researchers at MIT and Pierre et Marie Curie University in Paris have analyzed the mechanical forces underpinning simple knots, and come up with a theory that describes how a knot’s topology determines its mechanical forces.

The researchers carried out experiments to test how much force is required to tighten knots with an increasing number of twists. They then compared their observations with their theoretical predictions, and found that the theory accurately predicted the force needed to close a knot, given its topology and the diameter and stiffness of the underlying strand.

“This is the first time, to the best of our knowledge, that precision model experiments and theory have been tied together to untangle the influence of topology on the mechanics of knots,” the researchers write in a paper appearing in the journal Physical Review Letters.

Pedro Reis, the Gilbert W. Winslow Career Development Associate Professor in Civil Engineering and Mechanical Engineering, says the new knot theory may provide guidelines for choosing certain knot configurations for a given load-bearing application, such as braided steel cables, or surgical stitching patterns.

“Surgeons, of course, have a great deal of experience, and they know this knot is better for this stitching procedure than this knot,” Reis says. “But can we further inform the process? While maybe these knots are used, we might show that some other knots, done in a certain way, may be preferable.”

A twisted theory

Reis’ colleague, French theoretician Basile Audoly, originally took on the problem of relating a knot’s topology and mechanical forces. In previous work, Audoly, with his own colleague Sébastien Neukirch, had developed a theory based on observations of tightening a very simple, overhand knot, comprising only one twist. They then verified the theory with a slightly more complex knot with two twists. The theory, they concluded, should predict the forces required to tighten even more complex knots.

However, when Reis, together with his students Khalid Jawed and Peter Dieleman, performed similar experiments with knots of more than two twists, they found that the previous theory failed to predict the force needed to close the knots. Reis and Audoly teamed up to develop a more accurate theory for describing the topology and mechanics of a wider range of knots.

The researchers created knots from nitonol, a hyper-elastic wire that, even when bent at dramatic angles, will return to its original shape. Nitonol’s elasticity and stiffness are well known.

To generate various topologies, the researchers tied knots with multiple overhand twists, creating increasingly longer braids. They then clamped one end of each braid to a table, used a mechanical arm to simultaneously pull the knot tight, and measured the force applied. From these experiments, they observed that a knot with 10 twists requires about 1,000 times more force to close than a knot with just one.

“When Pedro Reis showed me his experiments on knots with as much as 10 twists, and told me that they could resist such a high force, this first appeared to me to be far beyond what simple equations can capture,” Audoly says. “Then, I thought it was a nice challenge.”

From shoelaces to surgery

To come up with a theory to predict the forces observed, Reis and Audoly went through multiple iterations between the experiments and theory to identify the ingredients that mattered the most and simplify the model. Eventually, they divided the problem in two parts, first characterizing the knot’s loop, then its braid. For the first part, the researchers quantified the aspect ratio, or shape of a loop, given the number of twists in a braid: The more twists in a braid, the more elliptical the loop.

The team then studied the forces within the braid. As a braid, or twist, is symmetric, the researchers simplified the problem by only considering one strand of the braid.

“Then we write an energy for the system that includes bending, tension, and friction for that one helical strand, and we are able to determine the shape,” Audoly says. “Once we have the shape, we can match it to this loop, and ultimately we get the overall force displacement response of the system.”

To test the theory, Reis plugged the experiments’ measurements into the theory to generate predictions of force.

“When we put the data through the machinery of the theory, the predictions and the dataset all collapse onto this master curve,” Reis says. “Once we have this master curve, you can give me a bending stiffness and diameter of a strand, and the number of turns in the knot, and I can tell you what force is required to close it. Also, we now understand how the knot locks itself up when more turns are added.”

Reis envisions multiple applications for the group’s theory, both significant and mundane.

“This theory helps us predict the mechanical response of knots of different topologies,” Reis says. “We’re describing the force it requires to close a loop, which is an indicator of the stiffness of the knot. This might help us to understand something as simple as how your headphones get tangled, and how to better tie your shoes, to how the configuration of knots can help in surgical procedures.”

Story Source:

The above post is reprinted from materials provided by Massachusetts Institute of Technology. The original item was written by Jennifer Chu. Note: Materials may be edited for content and length.

20 Tips To Hack An Interview


Interviews,especially job interviews are dreaded by almost everyone at some stage in life. Some dread it less and some get hyper-nervous. But it is no cakewalk for anyone. Definitely not for a college student, who, after long years of studying and enjoying is preparing to face the music.

While each interview is different, there are some general things you need to keep in mind before you go for it. The following tips comprise of both the general as well as some cool tips unknown to most job seekers, which can help you crack an interview.

1. Know what you want

I think the first tip for cracking a job interview is to go for the right job interview. A lot of times college students go for the wrong job; something which they know they’d dislike sooner or later. They usually succumb to peer pressure and follow the herd.

It’s true that we don’t always know what we want, especially right after college when the primary focus is to land a job and start raking in the moolah. That is okay but going for a job which is aligned to your interests will always shape up a great career for you. So think about it for a moment and decide on the interview you should appear for. Listen to your heart and then go for it.

2. Prepare, and then prepare a little more

You may have been the topper at your university and fetched medals in all sorts of activities. Good for you. But that doesn’t guarantee your success in the interview. The HR representatives from corporate firms are a different breed and being complacent is the last thing you can afford to do.

Hence, no matter how confident you feel (which is a great feeling to have), make sure you leave no stone unturned in preparing for the interview. And that means preparing for the common interview questions, refining your communication skills, taking advice from others and more. Here’s a list of common interview questions for your reference.

3. Study and get to know the firm

This is a very basic mistake which a lot of newbies tend to make. They are up for the interview but when asked what do they know about the firm, they don’t have much to say. That’s because they haven’t spent time checking the company’s website and googling its name to check its web presence.

Don’t be a noob. Do an in-depth study about the firm on the internet. Check their Wikipedia page if they have one, check their site, google their name, check who the founders are, check what does the company specialize in…all this will ensure that you leave a great impression on the interviewer when he asks what do you know about their firm.

4. Get your online profiles in order

While you are checking the firm online, don’t forget that they could check you online too. College students are known to be active on social networks and many companies now-a-days prefer to do a thorough online research about their job applicants. Hence it is important that you check out all your online profiles and make sure that you clear anything which you feel could obstruct your success in the interview.

5. Say “I don’t know” when you don’t know

Remember the interview of Chris Gardner (Will Smith) in The Pursuit of Happyness? He tells the interviewer, “I’m the type of person that if you ask me a question and I don’t know the answer, I’m gonna tell you that I don’t know. But I bet you what, I know how to find the answer and I will find the answer.” And he gets the job.

So be upfront and truthful. Don’t try to fake skills because there are strong chances you will get caught right there.

6. Don’t be aggressive

While it’s good to say I don’t know when you don’t know, it could be a possibility that you do know just about everything the person asks. And you might know much more than what the interviewer had expected. But this is where the problem begins. You tend to become aggressive and argue loudly.

Don’t let your confidence become your arrogance. Be calm and to the point when answering questions. You may consider being assertive but don’t try to be aggressive.

7. Have the right attitude

Have you ever wondered why a candidate gets the job even when he seemed far less qualified than the job profile required him to be ? Well, the answer is – attitude matters. And he had the right attitude towards the job. He was calm, curious, listened actively and demonstrated his potential to excel in the job, no matter what his qualifications are. That’s what you need to keep in mind too. Go in the interview room with the mindset that you will come out with an offer letter. Don’t treat it like just another interview.

8. Practice

Practice what, you may ask. Well, practice the interview…in front of the mirror. Yeah, you read it right. It’s old fashioned but still and will continue to be very effective. It can help you study your facial gestures and see where you need to improve. Plus it boosts your confidence.

You could also practice with your friends and classmates. Do role plays and try to create an environment of a real interview.

9. Think before you speak

Most of the time the interviewee assumes that his success in the interview depends on how quick he can respond to every question. And hence many times he says something which he shouldn’t have said. Therefore it is important that you don’t tread that path. There is no harm if you take a minute or two to think if you are stuck at a question. Ultimately, what you answer matters the most.

10. Begging for job

Emotional blackmails might work on some interviewers and you might get the job on the grounds of sympathy, but I’d say the chances are 1 in 100. You beg for the job and you lose the respect of the interviewer. It’s very hard to try any other trick on him after that. So don’t plead for the job. You would get it if you prove that you deserve it. Not by any other way.

11. Smile often

While crying and begging usually doesn’t work, smiling does. A smiling face often has a positive impact on the person on the other side. It makes the applicant appear confident and easy going. Of course for the candidate, a smile can do a great deal in reducing the nervousness and perform better in the interview.

12. Never badmouth college authorities or previous employers

No matter how much you hated your professors or any previous boss when you did a summer job, make sure you don’t tell that to the interviewer. This is when not being truthful is better. You don’t have to sing songs in their praise, just speak well of them.

By asking such questions, the interviewer will try to judge how comfortable you are under authority. That’s because you’ll have a boss at the job. So badmouthing your college authorities could leave a negative impression on him.

13. Money isn’t everything

It may be everything but you don’t have to show that in the interview. Also, as I mentioned earlier, you should go for a job which you know you would be interested in. Because when you appear for that interview, you would be enthusiastic about your future prospects irrespective of the money you’d make. And that is music to the interviewer’s ears.

14. Resume

How could I forget one of the most important things in an interview, especially when the applicant is a fresher just out of college. Your resume should clearly reflect what you were and what you are capable of.
A resume which is nicely done gives you an advantage over other candidates.

15. Be precise and clear

A common complaint which HR managers have when they interview college students is that the interviewees tend to beat around the bush and waste their time. That is again an indication of not preparing well for the interview.

So make sure that you answer precisely and clearly. Don’t add unnecessary sentences because that could give the interviewer a chance to grill you more.

16. Social networking

The importance of social networking before an interview is often ignored by the candidates. If you have a job interview coming up, why not go to LinkedIn or Facebook and try to find people who recently joined that firm. And then try to contact them to get some pointers. This is just one example of how you could utilize the social networks to prepare for the interview.

17. Take advice from seniors and professors

That’s why it is always advisable for a college student to maintain a healthy relationship with his seniors and professors. They are the ones who could give the most valuable tips which could help you crack the interview. So don’t forget to take advice from them before the D-day.

18. Ask questions to the interviewer

Every interviewer gives a chance to the applicant to ask him questions about the job and the company. You should utilize this opportunity to ask relevant questions about the job. Shying away from asking questions at this point could mean that you aren’t very enthusiastic about the new opportunity.

19. Switch off your cellphone

A simple but an important thing to do before the interview. It shows you are really serious about getting the job. In fact a better step could be not to carry your cellphone at all to the interview. That would eliminate the possibility of your cellphone ringing suddenly in case you forgot to switch it off.

20. Your posture and eye-contact

The way you sit and look at the interviewer matters a lot. It’s also a part of having the right attitude. Sit straight and have a constant eye contact with the interviewer. It shows that you are confident and ready to enter the corporate world.

50 Common Interview Questions and Tips


50 Common Interview Questions and Tips:

Review these typical interview questions and think about how you would answer them. Read the questions listed; you will also find some strategy suggestions with it.

1. Tell me about yourself:

The most often asked question in interviews. You need to have a short statement prepared in your mind. Be careful that it does not sound rehearsed. Limit it to work-related items unless instructed otherwise. Talk about things you have done and jobs you have held that relate to the position you are interviewing for. Start with the item farthest back and work up to the present.

2. Why did you leave your last job?

Stay positive regardless of the circumstances. Never refer to a major problem with management and never speak ill of supervisors, co- workers or the organization. If you do, you will be the one looking bad. Keep smiling and talk about leaving for a positive reason such as an opportunity, a chance to do something special or other forward- looking reasons.

3. What experience do you have in this field?

Speak about specifics that relate to the position you are applying for. If you do not have specific experience, get as close as you can.

4. Do you consider yourself successful?

You should always answer yes and briefly explain why. A good explanation is that you have set goals, and you have met some and are on track to achieve the others.

5. What do co-workers say about you?

Be prepared with a quote or two from co-workers. Either a specific statement or a paraphrase will work. Jill Clark, a co-worker at Smith Company, always said I was the hardest workers she had ever known. It is as powerful as Jill having said it at the interview herself.

6. What do you know about this organization?

This question is one reason to do some research on the organization before the interview. Find out where they have been and where they are going. What are the current issues and who are the major players?

7. What have you done to improve your knowledge in the last year?

Try to include improvement activities that relate to the job. A wide variety of activities can be mentioned as positive self-improvement. Have some good ones handy to mention.

8. Are you applying for other jobs?

Be honest but do not spend a lot of time in this area. Keep the focus on this job and what you can do for this organization. Anything else is a distraction.

9. Why do you want to work for this organization?

This may take some thought and certainly, should be based on the research you have done on the organization. Sincerity is extremely important here and will easily be sensed. Relate it to your long-term career goals.

10. Do you know anyone who works for us?

Be aware of the policy on relatives working for the organization. This can affect your answer even though they asked about friends not relatives. Be careful to mention a friend only if they are well thought of.

11. What kind of salary do you need?
A loaded question. A nasty little game that you will probably lose if you answer first. So, do not answer it. Instead, say something like, That’s a tough question. Can you tell me the range for this position? In most cases, the interviewer, taken off guard, will tell you. If not, say that it can depend on the details of the job. Then give a wide range.

12. Are you a team player?
You are, of course, a team player. Be sure to have examples ready. Specifics that show you often perform for the good of the team rather than for yourself are good evidence of your team attitude. Do not brag, just say it in a matter-of-fact tone. This is a key point.

13. How long would you expect to work for us if hired?

Specifics here are not good. Something like this should work: I’d like it to be a long time. Or As long as we both feel I’m doing a good job.
14. Have you ever had to fire anyone? How did you feel about that?

This is serious. Do not make light of it or in any way seem like you like to fire people. At the same time, you will do it when it is the right thing to do. When it comes to the organization versus the individual who has created a harmful situation, you will protect the organization. Remember firing is not the same as layoff or reduction in force.

15. What is your philosophy towards work?

The interviewer is not looking for a long or flowery dissertation here. Do you have strong feelings that the job gets done? Yes. That’s the type of answer that works best here. Short and positive, showing a benefit to the organization.

16. If you had enough money to retire right now, would you?

Answer yes if you would. But since you need to work, this is the type of work you prefer. Do not say yes if you do not mean it.

17. Have you ever been asked to leave a position?

If you have not, say no. If you have, be honest, brief and avoid saying negative things about the people or organization involved.

18. Explain how you would be an asset to this organization.

You should be anxious for this question. It gives you a chance to highlight your best points as they relate to the position being discussed. Give a little advance thought to this relationship.

19. Why should we hire you?

Point out how your assets meet what the organization needs. Do not mention any other candidates to make a comparison.

20. Tell me about a suggestion you have made.

Have a good one ready. Be sure and use a suggestion that was accepted and was then considered successful. One related to the type of work applied for is a real plus.

21. What irritates you about co-workers?

This is a trap question. Think real hard but fail to come up with anything that irritates you. A short statement that you seem to get along with folks is great.

22. What is your greatest strength?

Numerous answers are good, just stay positive. A few good examples: Your ability to prioritize, Your problem-solving skills, Your ability to work under pressure, Your ability to focus on projects, Your professional expertise, Your leadership skills, Your positive attitude

23. Tell me about your dream job.

Stay away from a specific job. You cannot win. If you say the job you are contending for is it, you strain credibility. If you say another job is it, you plant the suspicion that you will be dissatisfied with this position if hired. The best is to stay genetic and say something like: A job where I love the work, like the people, can contribute and can’t wait to get to work.

24. Why do you think you would do well at this job?

Give several reasons and include skills, experience and interest.

25. What are you looking for in a job?

See answer # 23

26. What kind of person would you refuse to work with?

Do not be trivial. It would take disloyalty to the organization, violence or lawbreaking to get you to object. Minor objections will label you as a whiner.

27. What is more important to you: the money or the work?

Money is always important, but the work is the most important. There is no better answer.

28. What would your previous supervisor say your strongest point is?

There are numerous good possibilities:
Loyalty, Energy, Positive attitude, Leadership, Team player, Expertise, Initiative, Patience, Hard work, Creativity, Problem solver

29. Tell me about a problem you had with a supervisor.

Biggest trap of all. This is a test to see if you will speak ill of your boss. If you fall for it and tell about a problem with a former boss, you may well below the interview right there. Stay positive and develop a poor memory about any trouble with a supervisor.

30. What has disappointed you about a job?

Don’t get trivial or negative. Safe areas are few but can include:
Not enough of a challenge. You were laid off in a reduction Company did not win a contract, which would have given you more responsibility.

31. Tell me about your ability to work under pressure.

You may say that you thrive under certain types of pressure. Give an example that relates to the type of position applied for.

32. Do your skills match this job or another job more closely?

Probably this one. Do not give fuel to the suspicion that you may want another job more than this one.

33. What motivates you to do your best on the job?

This is a personal trait that only you can say, but good examples are: Challenge, Achievement, Recognition

34. Are you willing to work overtime? Nights? Weekends?

This is up to you. Be totally honest.

35. How would you know you were successful on this job?

Several ways are good measures:
You set high standards for yourself and meet them. Your outcomes are a success.Your boss tell you that you are successful

36. Would you be willing to relocate if required?

You should be clear on this with your family prior to the interview if you think there is a chance it may come up. Do not say yes just to get the job if the real answer is no. This can create a lot of problems later on in your career. Be honest at this point and save yourself uture grief.

37. Are you willing to put the interests of the organization ahead of your own?

This is a straight loyalty and dedication question. Do not worry about the deep ethical and philosophical implications. Just say yes.

38. Describe your management style.

Try to avoid labels. Some of the more common labels, like progressive, salesman or consensus, can have several meanings or descriptions depending on which management expert you listen to. The situational style is safe, because it says you will manage according to the situation, instead of one size fits all.

39. What have you learned from mistakes on the job?

Here you have to come up with something or you strain credibility. Make it small, well intentioned mistake with a positive lesson learned. An example would be working too far ahead of colleagues on a project and thus throwing coordination off.

40. Do you have any blind spots?

Trick question. If you know about blind spots, they are no longer blind spots. Do not reveal any personal areas of concern here. Let them do their own discovery on your bad points. Do not hand it to them.

41. If you were hiring a person for this job, what would you look for?

Be careful to mention traits that are needed and that you have.

42. Do you think you are overqualified for this position?

Regardless of your qualifications, state that you are very well qualified for the position.

43. How do you propose to compensate for your lack of experience?

First, if you have experience that the interviewer does not know about, bring that up: Then, point out (if true) that you are a hard working quick learner.

44. What qualities do you look for in a boss?

Be generic and positive. Safe qualities are knowledgeable, a sense of humor, fair, loyal to subordinates and holder of high standards. All bosses think they have these traits.

45. Tell me about a time when you helped resolve a dispute between others.

Pick a specific incident. Concentrate on your problem solving technique and not the dispute you settled.

46. What position do you prefer on a team working on a project?

Be honest. If you are comfortable in different roles, point that out.

47. Describe your work ethic.

Emphasize benefits to the organization. Things like, determination to get the job done and work hard but enjoy your work are good.

48. What has been your biggest professional disappointment?

Be sure that you refer to something that was beyond your control. Show acceptance and no negative feelings.

49. Tell me about the most fun you have had on the job.

Talk about having fun by accomplishing something for the organization.

50. Do you have any questions for me?

Always have some questions prepared. Questions prepared where you will be an asset to the organization are good. How soon will I be able to be productive? and What type of projects will I be able to assist on? are examples.

And Finally Good Luck


Earth Has More Than 3 Trillion Trees

Using a combination of satellite imagery, forest inventories, and supercomputer technologies, the researchers were able to produce a global map of tree density at the square-kilometer pixel scale. Credit: Image courtesy of Yale School of Forestry & Environmental Studies
Using a combination of satellite imagery, forest inventories, and supercomputer technologies, the researchers were able to produce a global map of tree density at the square-kilometer pixel scale.
Credit: Image courtesy of Yale School of Forestry & Environmental Studies

[dropcap]A[/dropcap] new Yale-led study estimates that there are more than 3 trillion trees on Earth, about seven and a half times more than some previous estimates. But the total number of trees has plummeted by roughly 46 percent since the start of human civilization, the study estimates.

Using a combination of satellite imagery, forest inventories, and supercomputer technologies, the international team of researchers was able to map tree populations worldwide at the square-kilometer level.

Their results, published in the journal Nature, provide the most comprehensive assessment of tree populations ever produced and offer new insights into a class of organism that helps shape most terrestrial biomes.

The new insights can improve the modeling of many large-scale systems, from carbon cycling and climate change models to the distribution of animal and plant species, say the researchers.

“Trees are among the most prominent and critical organisms on Earth, yet we are only recently beginning to comprehend their global extent and distribution,” said Thomas Crowther, a postdoctoral fellow at the Yale School of Forestry & Environmental Studies (F&ES) and lead author of the study.

“They store huge amounts of carbon, are essential for the cycling of nutrients, for water and air quality, and for countless human services,” he added. “Yet you ask people to estimate, within an order of magnitude, how many trees there are and they don’t know where to begin. I don’t know what I would have guessed, but I was certainly surprised to find that we were talking about trillions.”

The study was inspired by a request by Plant for the Planet, a global youth initiative that leads the United Nations Environment Programme’s “Billion Tree Campaign.” Two years ago the group approached Crowther asking for baseline estimates of tree numbers at regional and global scales so they could better evaluate the contribution of their efforts and set targets for future tree-planting initiatives.

At the time, the only global estimate was just over 400 billion trees worldwide, or about 61 trees for every person on Earth. That prediction was generated using satellite imagery and estimates of forest area, but did not incorporate any information from the ground.

The new study used a combination of approaches to reveal that there are 3.04 trillion trees — roughly 422 trees per person.

Crowther and his colleagues collected tree density information from more than 400,000 forest plots around the world. This included information from several national forest inventories and peer-reviewed studies, each of which included tree counts that had been verified at the ground level. Using satellite imagery, they were then able to assess how the number of trees in each of those plots is related to local characteristics such as climate, topography, vegetation, soil condition, and human impacts.

“The diverse array of data available today allowed us to build predictive models to estimate the number of trees at each location around the globe,” said Yale postdoctoral student Henry Glick, second author of the study.

The resulting map has the potential to inform scientists about the structure of forest ecosystems in different regions, and it can be used to improve predictions about carbon storage and biodiversity around the world.

“Most global environmental data is thematically coarse,” said Matthew Hansen, a global forestry expert from the University of Maryland who was not involved in the study. “The study of Crowther et al. moves us towards a needed direct quantification of tree distributions, information ready to be used by a host of downstream science investigations.”

The highest densities of trees were found in the boreal forests in the sub-arctic regions of Russia, Scandinavia, and North America. But the largest forest areas, by far, are in the tropics, which are home to about 43 percent of the world’s trees. (Only 24 percent are in the dense boreal regions, while another 22 percent exist in temperate zones.)

The results illustrate how tree density changes within forest types. Researchers found that climate can help predict tree density in most biomes. In wetter areas, for instance, more trees are able to grow. However, the positive effects of moisture were reversed in some regions because humans typically prefer the moist, productive areas for agriculture.

In fact, human activity is the largest driver of tree numbers worldwide, said Crowther. While the negative impact of human activity on natural ecosystems is clearly visible in small areas, the study provides a new measure of the scale of anthropogenic effects, highlighting how historical land use decisions have shaped natural ecosystems on a global scale. In short, tree densities usually plummet as the human population increases. Deforestation, land-use change, and forest management are responsible for a gross loss of over 15 billion trees each year.

“We’ve nearly halved the number of trees on the planet, and we’ve seen the impacts on climate and human health as a result,” Crowther said. “This study highlights how much more effort is needed if we are to restore healthy forests worldwide.”

Researchers from 15 countries collaborated on the study.

Story Source:

The above post is reprinted from materials provided by Yale School of Forestry & Environmental Studies. Note: Materials may be edited for content and length.

Journal Reference:

  1. T. W. Crowther, H. B. Glick, K. R. Covey, C. Bettigole, D. S. Maynard, S. M. Thomas, J. R. Smith, G. Hintler, M. C. Duguid, G. Amatulli, M.-N. Tuanmu, W. Jetz, C. Salas, C. Stam, D. Piotto, R. Tavani, S. Green, G. Bruce, S. J. Williams, S. K. Wiser, M. O. Huber, G. M. Hengeveld, G.-J. Nabuurs, E. Tikhonova, P. Borchardt, C.-F. Li, L. W. Powrie, M. Fischer, A. Hemp, J. Homeier, P. Cho, A. C. Vibrans, P. M. Umunay, S. L. Piao, C. W. Rowe, M. S. Ashton, P. R. Crane, M. A. Bradford. Mapping tree density at a global scale. Nature, 2015; DOI: 10.1038/nature14967

Sending Magnetic Signals Through Your Body

Magnetic fields provide a new way to communicate wirelessly

A new technique could pave the way for ultra low power and high-security wireless communication systems

This is a prototype of the magnetic field human body communication, developed in Mercier's Energy-Efficient Microsystems Lab at UC San Diego, consists of magnetic-field-generating coils wrapped around three parts of the body, including the head, arm and leg. Credit: Jacobs School of Engineering, UC San Diego
This is a prototype of the magnetic field human body communication, developed in Mercier’s Energy-Efficient Microsystems Lab at UC San Diego, consists of magnetic-field-generating coils wrapped around three parts of the body, including the head, arm and leg.
Credit: Jacobs School of Engineering, UC San Diego

[dropcap]E[/dropcap]lectrical engineers at the University of California, San Diego demonstrated a new wireless communication technique that works by sending magnetic signals through the human body. The new technology could offer a lower power and more secure way to communicate information between wearable electronic devices, providing an improved alternative to existing wireless communication systems, researchers said. They presented their findings Aug. 26 at the 37th Annual International Conference of the IEEE Engineering in Medicine and Biology Society in Milan, Italy.

While this work is still a proof-of-concept demonstration, researchers envision developing it into an ultra low power wireless system that can easily transmit information around the human body. An application of this technology would be a wireless sensor network for full-body health monitoring.

“In the future, people are going to be wearing more electronics, such as smart watches, fitness trackers and health monitors. All of these devices will need to communicate information with each other. Currently, these devices transmit information using Bluetooth radios, which use a lot of power to communicate. We’re trying to find new ways to communicate information around the human body that use much less power,” said Patrick Mercier, a professor in the Department of Electrical and Computer Engineering at UC San Diego who led the study. Mercier also serves as the co-director of the UC San Diego Center for Wearable Sensors.

Communicating magnetic signals through the human body

The new study presents a solution to some of the main barriers of other wireless communication systems: in order to reduce power consumption when transmitting and receiving information, wireless systems need to send signals that can easily travel from one side of the human body to another. Bluetooth technology uses electromagnetic radiation to transmit data, however these radio signals do not easily pass through the human body and therefore require a power boost to help overcome this signal obstruction, or “path loss.”

In this study, electrical engineers demonstrated a technique called magnetic field human body communication, which uses the body as a vehicle to deliver magnetic energy between electronic devices. An advantage of this system is that magnetic fields are able to pass freely through biological tissues, so signals are communicated with much lower path losses and potentially, much lower power consumption. In their experiments, researchers demonstrated that the magnetic communication link works well on the body, but they did not test the technique’s power consumption. Researchers showed that the path losses associated with magnetic field human body communication are upwards of 10 million times lower than those associated with Bluetooth radios.

“This technique, to our knowledge, achieves the lowest path losses out of any wireless human body communication system that’s been demonstrated so far. This technique will allow us to build much lower power wearable devices,” said Mercier.

Lower power consumption also leads to longer battery life. “A problem with wearable devices like smart watches is that they have short operating times because they are limited to using small batteries. With this magnetic field human body communication system, we hope to significantly reduce power consumption as well as how frequently users need to recharge their devices,” said Jiwoong Park, a Ph.D student in Mercier’s Energy-Efficient Microsystems Lab at the UC San Diego Jacobs School of Engineering and first author of the study.

The researchers also pointed out that this technique does not pose any serious health risks. Since this technique is intended for applications in ultra low power communication systems, the transmitting power of the magnetic signals sent through the body is expected to be many times lower than that of MRI scanners and wireless implant devices.

Another potential advantage of magnetic field human body communication is that it could offer more security than Bluetooth networks. Because Bluetooth radio communicates data over the air, anyone standing within 30 feet can potentially eavesdrop on that communication link. On the other hand, magnetic field human body communication employs the human body as a communication medium, making the communication link less vulnerable to eavesdropping. With this technique, researchers demonstrated that magnetic communication is strong on the body but dramatically decreases off the body. To put this in the context of a personal full-body wireless communication network, information would neither be radiated off the body nor be transmitted from one person to another.

“Increased privacy is desirable when you’re using your wearable devices to transmit information about your health,” said Park.

Demonstrating magnetic communication with a proof-of-concept prototype

The researchers built a prototype to demonstrate the magnetic field human body communication technique. The prototype consists of copper wires insulated with PVC tubes. On one end, the copper wires are hooked up to an external analyzer and on the other end, the wires are wrapped in coils around three areas of the body: the head, arms and legs. These coils serve as sources for magnetic fields and are able to send magnetic signals from one part of the body to another using the body as a guide. With this prototype, researchers were able to demonstrate and measure low path loss communication from arm to arm, from arm to head, and from arm to leg.

Researchers noted that a limitation of this technique is that magnetic fields require circular geometries in order to propagate through the human body. Devices like smart watches, headbands and belts will all work well using magnetic field human body communication, but not a small patch that is stuck on the chest and used to measure heart rate, for example. As long as the wearable application can wrap around a part of the body, it should work just fine with this technique, researchers explained.

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The above post is reprinted from materials provided by University of California – San Diego. Note: Materials may be edited for content and length.

What is the Difference Between a Disc and a Disk?

In computers, disks are used for the storage of data.
In computers, disks are used for the storage of data.

Origin of Disc and Disk

For the most part, the words “disc” and “disk” can be used interchangeably to describe flat, rounded objects. The British tend to prefer “disc,” and Americans generally use “disk” as their default spelling. In some cases, the spelling with a “k” at the end is based on Germanic origins, and the spelling with a “c” at the end is based on Greek or Latin origins. The use of “disc” or “disk,” however, is often simply a matter of preference within a particular field of use. No matter the field or the typical spelling for a particular object, it is not unusual to see the other spelling used, even by respected sources.

The word “disk” entered the popular vernacular first, sometime during the 17th century. By the 18th century, however, there was a movement toward incorporating Latin roots whenever possible. The Latin word discus led to the use of “disc” to refer to thin, circular objects.

In Real World

Discs or disks appear in fields such as computers, media, science, anatomy and automotive mechanics. Some of these fields primarily use one spelling, and others use both, depending on the specific object. In many fields, the spellings can be used interchangeably.

Compact discs can store data.
Compact discs can store data.

In computers and media, “discs” or “disks” typically refer to storage devices for data, music and videos. Phonographic records were also known as discs, and people who played records on radio stations were called disc jockeys. When optical storage devices were introduced, this spelling carried over into compact discs (CDs) and digital versatile discs (DVDs). Magnetic storage devices often use the spelling with a “k” as seen in floppy disks and computer hard disks.

Anatomical objects typically use the “disc” spelling. For example, a healthcare professional might refer to a “herniated disc” when a patient has a certain injury to the fibrocartilage between vertebrae in the spine. Other discs in the human body include optic discs in the eyes and placental discs in females.

"Disc" is commonly used in the context of the spine and spinal injuries like disc herniation.
“Disc” is commonly used in the context of the spine and spinal injuries like disc herniation.

In automotive mechanics, a disc brake is a device that uses friction against a circular metal plate to slow or stop the vehicle’s wheel.

In astronomy, the shape of a galaxy might be described as a disc. A ring of debris orbiting an object such as a star, on the other hand, typically is referred to as a debris disk.





Source / Courtesy : WiseGeek

Key tips to Write Resume

Resume Writing Tips Winged Post

Hiring managers and recruiters alike say they’ve seen more poorly written resumes cross their desks recently than ever before. Attract more interview offers and ensure your resume doesn’t eliminate you from consideration by following these six key tips to write resume:

1.   Format Your Resume Wisely “Do the Hiring Managers” Work for Them

No matter how well written, your resume won’t get a thorough reading the first time through. Generally a resume gets scanned for 25 seconds. Scanning is more difficult if it is hard to read, poorly organized or exceeds two pages.

  • Use a logical format and wide margins, clean type and clear headings
  • Selectively apply bold and italic typeface that help guide the reader’s eye
  • Use bullets to call attention to important points (i.e. accomplishments)

2.   Identify Accomplishments not Just Job Descriptions

Hiring managers, especially in technical fields like engineering, seek candidates that can help them solve a problem or satisfy a need within their company. Consequently, you can’t be a solution to their problems without stating how you solved similar problems in other companies and situations.

  • Focus on what you did in the job, NOT what your job was there’s a difference
  • Include a one or two top line job description first, then list your accomplishments
  • For each point ask yourself, What was the benefit of having done what I did?
  • Accomplishments should be unique to you, not just a list of what someone else did
  • Avoid using the generic descriptions of the jobs you originally applied for or held

3.   Quantify Your Accomplishments

Q: What’s the most common resume mistake?
A: Making too many general claims and using too much industry jargon that does not market the candidate. A resume is a marketing document designed to sell your skills and strengths rather than just portray a bio of the candidate.

  • Include and highlight specific achievements that present a comprehensive picture of your marketability
  • Quantify your achievements to ensure greater confidence in the hiring manager and thereby generate interest percentages, dollars, number of employees, etc.
  • Work backwards to quantify your accomplishments by asking, If I had not done X, what could have happened?

4.   Cater Your Resume for the Industry

Unlike advertising and design professionals who have greater creative license in designing their resume for those fields, the mechanical engineering industry won’t be impressed and may be turned off by distinctive resume design.

  • Err on the side of being conservative stylistically
  • Your accomplishments, error-free writing, grammatically-correct, clean, crisp type and paper will make the impression for you

5.   Replace your Objective” with a “Career Summary”

A Career Summary is designed to give a brief overview of who you are and what you do. Most Objectives sound similar: Seeking a challenging, interesting position in X where I can use my skills of X, Y, and Z to contribute to the bottom line. Not telling at all.

  • Grab a hiring manager’s attention right from the beginning, remembering you
    have only 25 few seconds to make a good impression
  • Spend time developing a summary that immediately gets their attention, and accurately and powerfully describes you as a solution to their problems

6.   Network. Network. Network.

For unemployed candidates, handing out resumes should be a full-time job. The majority of mid- to senior-level positions are filled through networking, so contact absolutely everyone you know in addition to recruiters who are in a position to hire you or share insights. Networking can include

  • Personal business contacts, people you’ve worked for or who worked for you
  • Vendors and sales representatives you’ve dealt with in the past five years
  • People listed in the alumni directory of your alma mater

With a solid resume in hand you’ll greatly increase your odds of earning a closer look and getting that interview.

If you have any questions, just post your queries in the comment box below and we will get back to you.


Milestone in Hybrid Artificial Photosynthesis

Artificial photosynthesis used to produce renewable molecular hydrogen for synthesizing carbon dioxide into methane. Credit: Berkeley Lab
Artificial photosynthesis used to produce renewable molecular hydrogen for synthesizing carbon dioxide into methane.
Credit: Berkeley Lab

A team of researchers at the U.S. Department of Energy (DOE)’s Lawrence Berkeley National Laboratory (Berkeley Lab) developing a bioinorganic hybrid approach to artificial photosynthesis have achieved another milestone. Having generated quite a buzz with their hybrid system of semiconducting nanowires and bacteria that used electrons to synthesize carbon dioxide into acetate, the team has now developed a hybrid system that produces renewable molecular hydrogen and uses it to synthesize carbon dioxide into methane, the primary constituent of natural gas.

“This study represents another key breakthrough in solar-to-chemical energy conversion efficiency and artificial photosynthesis,” says Peidong Yang, a chemist with Berkeley Lab’s Materials Sciences Division and one of the leaders of this study. “By generating renewable hydrogen and feeding it to microbes for the production of methane, we can now expect an electrical-to-chemical efficiency of better than 50 percent and a solar-to-chemical energy conversion efficiency of 10-percent if our system is coupled with state-of-art solar panel and electrolyzer.”

Yang, who also holds appointments with UC Berkeley and the Kavli Energy NanoScience Institute (Kavli-ENSI) at Berkeley, is one of three corresponding authors of a paper describing this research in the Proceedings of the National Academy of Sciences (PNAS). The paper is titled “A hybrid bioinorganic approach to solar-to-chemical conversion.” The other corresponding authors are Michelle Chang and Christopher Chang. Both also hold joint appointments with Berkeley Lab and UC Berkeley. In addition, Chris Chang is a Howard Hughes Medical Institute (HHMI) investigator.

Photosynthesis is the process by which nature harvests the energy in sunlight and uses it to synthesize carbohydrates from carbon dioxide and water. Carbohyrates are biomolecules that store the chemical energy used by living cells. In the original hybrid artificial photosynthesis system developed by the Berkeley Lab team, an array of silicon and titanium oxide nanowires collected solar energy and delivered electrons to microbes which used them to reduce carbon dioxide into a variety of value-added chemical products. In the new system, solar energy is used to split the water molecule into molecular oxygen and hydrogen. The hydrogen is then transported to microbes that use it to reduce carbon dioxide into one specific chemical product, methane.

“In our latest work, we’ve demonstrated two key advances,” says Chris Chang. “First, our use of renewable hydrogen for carbon dioxide fixation opens up the possibility of using hydrogen that comes from any sustainable energy source, including wind, hydrothermal and nuclear. Second, having demonstrated one promising organism for using renewable hydrogen, we can now, through synthetic biology, expand to other organisms and other value-added chemical products.”

The concept in the two studies is essentially the same — a membrane of semiconductor nanowires that can harness solar energy is populated with bacterium that can feed off this energy and use it to produce a targeted carbon-based chemical. In the new study, the membrane consisted of indium phosphide photocathodes and titanium dioxide photoanodes. Whereas in the first study, the team worked with Sporomusa ovata, an anaerobic bacterium that readily accepts electrons from the surrounding environment to reduce carbon dioxide, in the new study the team populated the membrane with Methanosarcina barkeri, an anaerobic archaeon that reduces carbon dioxide using hydrogen rather than electrons.

“Using hydrogen as the energy carrier rather than electrons makes for a much more efficient process as molecular hydrogen, through its chemical bonds, has a much higher density for storing and transporting energy,” says Michelle Chang.

In the newest membrane reported by the Berkeley team, solar energy is absorbed and used to generate hydrogen from water via the hydrogen evolution reaction (HER). The HER is catalyzed by earth-abundant nickel sulfide nanoparticles that operate effectively under biologically compatible conditions. Hydrogen produced in the HER is directly utilized by the Methanosarcina barkeri archaeons in the membrane to produce methane.

“We selected methane as an initial target owing to the ease of product separation, the potential for integration into existing infrastructures for the delivery and use of natural gas, and the fact that direct conversion of carbon dioxide to methane with synthetic catalysts has proven to be a formidable challenge,” says Chris Chang. “Since we still get the majority of our methane from natural gas, a fossil fuel, often from fracking, the ability to generate methane from a renewable hydrogen source is another important advance.”

Adds Yang, “While we were inspired by the process of natural photosynthesis and continue to learn from it, by adding nanotechnology to help improve the efficiency of natural systems we are showing that sometimes we can do even better than nature.”

In addition to the corresponding authors, other co-authors of the PNAS paper describing this research were Eva Nichols, Joseph Gallagher, Chong Liu, Yude Su, Joaquin Resasco, Yi Yu and Yujie Sung.

This research was primarily funded by the DOE Office of Science.

Story Source:

The above post is reprinted from materials provided by Lawrence Berkeley National Laboratory. Note: Materials may be edited for content and length.

Journal Reference:

  1. Eva M. Nichols et al. Hybrid bioinorganic approach to solar-to-chemical conversion. PNAS, 2015 DOI: 10.1073/pnas.1508075112

July 2015 was warmest month ever recorded for the globe

Land and ocean temperature percentiles July 2015. Credit: NOAA
Land and ocean temperature percentiles July 2015
Credit: NOAA


The July average temperature across global land and ocean surfaces was 1.46°F (0.81°C) above the 20th century average. As July is climatologically the warmest month for the year, this was also the all-time highest monthly temperature in the 1880-2015 record, at 61.86°F (16.61°C), surpassing the previous record set in 1998 by 0.14°F (0.08°C). So July 2015 is the Warmest Month Ever!

Separately, the July globally-averaged land surface temperature was 1.73°F (0.96°C) above the 20th century average. This was the sixth highest for July in the 1880-2015 record.

The July globally-averaged sea surface temperature was 1.35°F (0.75°C) above the 20th century average. This was the highest temperature for any month in the 1880-2015 record, surpassing the previous record set in July 2014 by 0.13°F (0.07°C). The global value was driven by record warmth across large expanses of the Pacific and Indian Oceans.

The average Arctic sea ice extent for July was 350,000 square miles (9.5 percent) below the 1981-2010 average. This was the eighth smallest July extent since records began in 1979 and largest since 2009, according to analysis by the National Snow and Ice Data Center using data from NOAA and NASA.

Antarctic sea ice during July was 240,000 square miles (3.8 percent) above the 1981-2010 average. This was the fourth largest July Antarctic sea ice extent on record and 140,000 square miles smaller than the record-large July extent of 2014.

Global highlights: Year-to-date (January-July 2015)

  • The year-to-date temperature combined across global land and ocean surfaces was 1.53°F (0.85°C) above the 20th century average. This was the highest for January-July in the 1880-2015 record, surpassing the previous record set in 2010 by 0.16°F (0.09°C).
  • The year-to-date globally-averaged land surface temperature was 2.41°F (1.34°C) above the 20th century average. This was the highest for January-July in the 1880-2015 record, surpassing the previous record of 2007 by 0.27°F (0.15°C).
  • The year-to-date globally-averaged sea surface temperature was 1.21°F (0.67°C) above the 20th century average. This was also the highest for January-July in the 1880-2015 record, surpassing the previous record of 2010 by 0.11°F (0.06°C). Every major ocean basin observed record warmth in some areas.

Story Source:

The above post is reprinted from materials provided by National Oceanic and Atmospheric Administration. Note: Materials may be edited for content and length.

What is 4G Mobile Technology?

Fourth Generation (4G) mobile technology is a set of standards for providing broadband Internet access to devices like cellphones and tablets. Though it first became available in the US in 2009, no specific technologies were officially designated as 4G until 2011. Despite this, many devices were labeled as “4G” even though they did not meet the International Telecommunication Union’s (ITU) standards for the technology. The main difference between it and previous standards is a big increase in data transfer speeds and the types of media people can access with it.


There are also a number of technical specifications, including things like the wireless standard, radio interface, and frequency spectrum used. As of 2011, there were only two technologies officially designated as 4G mobile: LTE-Advanced and WiMax Release 2. Though devices using these technologies can theoretically reach the data speeds and functionality requirements set out by the ITU, the actual function varies according to the network coverage, infrastructure, and location.


Other Versions

Former versions of LTE and WiMax, and another technology called HSPA+, are also commonly referred to as 4G; despite the name, none actually meet the standards set out in IMT-A. The technologies were marketed so often as “4G” that the ITU allowed them to claim the designation. Most major carriers in the US work with at least one of these standards, with some supporting both. Generally speaking, LTE services are faster than WiMax, but WiMax can often support a farther-ranging signal than LTE, meaning that a user could conceivably use the mobile device farther away from a hotspot. Additionally, LTE is primarily used for cellphones and similar mobile devices, while WiMax is sometimes used to provide at-home Internet connections.

As Compared to 3G

The main difference between 4G mobile technology and the previous standard, 3G technology, in terms of end usage is the data transfer speeds provided. This means that users can access much more sophisticated data that requires a lot of bandwidth very quickly. Depending on the service provider, however, 4G mobile devices may be limited to specific zones for making phone calls that are generally smaller than the areas covered by 3G. This means that people trying to make a call would have their call dropped if they went outside the covered area. Some 4G phones also have much shorter battery life than most 3G phones.


Source / Courtesy : WiseGeek