Saturday, July 31, 2010
Uncertainty in the Presence of a Quantum Memory
A quantum particle is hard to grasp, because one cannot determine all its properties precisely at the same time. Measurements of certain parameter pairs such as position and momentum remain inaccurate to a degree given by Heisenberg's Uncertainty Principle. This is important for the security of quantum cryptography, where information is transmitted in the form of quantum states such as the polarization of particles of light. A group of scientists from LMU and the ETH in Zurich, including Professor Matthias Christandl, has now shown that position and momentum can be predicted more precisely than Heisenberg's Uncertainty Principle would lead one to expect, if the recipient makes use of a quantum memory that employs ions or atoms. The results show that the magnitude of the uncertainty depends on the degree of correlation ("entanglement") between the quantum memory and the quantum particle. "The result not only enhances our understanding of quantum memories, it also provides us with a method for determining the degree of correlation between two quantum particles," says Christandl. "Moreover, the effect we have observed could yield a means of testing the security of quantum cryptographic systems."
Unlike classical computers, quantum computers operate not with bits, but with quantum bits or qubits, quantum mechanical states of particles. The crucial feature of qubits is that they can exist in different states at once, not just 0 or 1, but also as a superposition of 0 and 1. The ability to exploit superposition states is what makes quantum computers potentially so powerful. "The goal of our research is to work out how quantum memories, i.e. memory systems for qubits, might be utilized in the future and how they affect the transmission of quantum bits," explains Christandl, who left LMU Munich in June 2010 to take up a position in the Institute of Theoretical Physics at the ETH in Zurich.
Heisenberg's Uncertainty Principle plays a central role in quantum computing, because it sets a fundamental limit to the accuracy with which a quantum state can be determined. Quantum mechanics also tells us that the measurement of a parameter can itself perturb the state of a particle. If, for example, one were to measure the position of a particle with infinite precision, the particle's momentum would become completely uncertain. Quantum cryptography uses this effect to encrypt data, for instance by entangling two quantum particles in a way that the probability with which the measurement of one particle yields a certain value depends on the state of the other particle. Eavesdropping can thus easily be uncovered, because any measurement will change the state of the particle measured.
The teams at LMU and the ETH Zurich have now shown that the result of a measurement on a quantum particle can be predicted with greater accuracy if information about the particle is available in a quantum memory. Atoms or ions can form the basis for such a quantum memory. The researchers have, for the first time, derived a formula for Heisenberg's Principle, which takes account of the effect of a quantum memory. In the case of so-called entangled particles, whose states are very highly correlated (i.e. to a degree that is greater than that allowed by the laws of classical physics), the uncertainty can disappear. According to Christandl, this can be roughly understood as follows "One might say that the disorder or uncertainty in the state of a particle depends on the information stored in the quantum memory. Imagine having a pile of papers on a table. Often these will appear to be completely disordered -- except to the person who put them there in the first place."
"Our results not only improve our understanding of quantum memories, they also give us a way of measuring entanglement," says Christandl. "The effect could also help us to test the security of quantum cryptographic systems." One can picture the method as a game in which player B transmits a particle to player A. A then performs a measurement on the particle, introducing an uncertainty. A subsequent measurement by B will only yield the value determined by A with an uncertainty given by Heisenberg's Principle."But if B uses a quantum memory," says Christandl, "he can determine the correct value and win the game."
The uncertainty principle in the presence of quantum memory
Mario Berta, Matthias Christandl, Roger Colbeck, Joseph M. Renes & Renato. Renner.
Nature Physics, published on line 25 July 2010; DOI: 10.1038/nphys1734
Link to Nature Physics abstract
That's what many college students do when asked to read an excerpt of a play for class, write a resume or find the e-mail address of a politician.
They trust Google so much that a Northwestern University study has found many students only click on websites that turn up at the top of Google searches to complete assigned tasks. If they don't use Google, researchers found that students trust other brand-name search engines and brand-name websites to lead them to information.
"Many students think, 'Google placed it number one, so, of course it's credible,'" said Eszter Hargittai, associate professor of communication studies at Northwestern. "This is potentially tricky because Google doesn't rank a site by its credibility."
In the published, study 102 students at the University of Illinois at Chicago sat at computers with researchers. Each student was asked to bring up the page that's usually on their screen when they start using the Web.
The activity on their screens was captured on video as researchers gave the students a variety of hypothetical information-seeking tasks to perform online. Time and again, researchers watched students navigate to brand-name search engines--usually Google--and to brand-name websites to find information. Researchers also asked students questions about websites they chose.
After using Google to get to a website, this interaction occurred between a researcher and a study participant:
Researcher: "What is this website?"
Student: "Oh, I don't know. The first thing that came up."
"Search engine rankings seem extremely important," Hargittai said. "We found that a website's layout or content almost didn't even matter to the students. What mattered is that it was the number one result on Google."
Aside from Google, other online brands that students mentioned most often to complete tasks were: Yahoo!, SparkNotes, MapQuest, Microsoft, Wikipedia, AOL and Facebook.
Some of the students did give more credibility to websites ending in dot-gov, dot-edu or dot-org. However, Hargittai said most didn't know dot-org domain names could be registered by anyone, and thus are not inherently different from dot-com sites.
"Just because younger people grew up with the Web doesn't mean they're universally savvy with it," Hargittai said. "Educators should show specific websites in class and talk about why a source is or isn't credible."
Trust Online: Young Adults' Evaluation of Web Content
Eszter Hargittai, Lindsay Fullerton, Ericka Menchen-Trevino, Kristin Yates Thomas
International Journal of Communication 4 (2010), 468–494 1932–8036/20100468
Link to IJOC article [pdf]
Friday, July 30, 2010
Overturning more than 40 years of accepted practice, new research proves that the tools used to check tests of "general mental ability" for bias are themselves flawed. This key finding from the Indiana University Kelley School of Business challenges reliance on such exams to make objective decisions for employment or academic admissions even in the face of well-documented gaps between mean scores of white and minority populations.
The study, published in the July issue of the Journal of Applied Psychology, investigated an amalgam of scores representing a vast sample of commonly used tests, including civil service or other pre-employment exams and university entrance exams.
"Test bias" means that two people with different ethnicity or gender, for example, who have the same test score are predicted to have different "scores" on the outcome (e.g., job performance); thus a biased test might benefit certain groups over others. Decades of earlier research consistently found no evidence of test bias against ethnic minorities, but the current study challenges this established belief.
"For generations, important decisions have been made about life-changing opportunities in employment and education based on results of these tests -- but we can no longer say with certainty they are unbiased," said Herman Aguinis, professor of organizational behavior and human resources and director of the Kelley School's new Institute for Global Organizational Effectiveness.
He led the study, which was co-authored by Steven A. Culpepper at the University of Colorado Denver and Charles A. Pierce at the University of Memphis.
"Our findings are significant because we proved that bias can be present but not be detected by even the top experts in the field, which could result in inaccurate prediction of outcomes such as job and academic performance for hundreds of thousands, if not millions, of individuals," Aguinis said.
To reach these conclusions, Aguinis and his co-authors created the largest simulation of its kind -- using nearly 16 million individual samples to yield more than eight trillion pairs of individual test/outcome scores. They built bias into most samples to resemble real-world results and used newly available super computing technology and power to check tens of billions of scores. They found the procedures in use today overwhelmingly and repeatedly missed the bias inserted in the data.
Few topics in human resource management have generated more public attention than bias in pre-employment and academic-admissions exams.
"The belief in the fairness of the tests and the accuracy of the gauges to check them has been so deeply engrained that to challenge them would be akin to questioning the sun as center of the solar system," said Aguinis, a nationally recognized expert who was also a co-author of an amicus brief in the landmark Ricci v. DeStefano Supreme Court case regarding employment testing.
"The irony is that for 40 years we have been trying to assess potential test bias with a biased procedure, and we now see that countless people may have been denied or given opportunities unfairly," he added. "From an ethical standpoint it may be argued that even if only one individual is affected this way, that is one too many. The problem is obviously magnified when we are dealing with hundreds of thousands, if not millions, of individuals taking standardized tests every year."
Prelude to a New Era?
Given the weight placed on such testing and the polarizing nature of the underlying racial/ethnic achievement gap, the authors expect the study will spur considerable controversy among the public and the academic, legal and policy communities, all of which will question the long-held belief that tests are unbiased.
They also anticipate a significant impact on the multi-billion dollar testing industry but made clear that they are not saying that any organization is deliberately using biased tests. However, as a preliminary step while more research is conducted, it is likely that many organizations will examine their existing tests and perhaps create new ones.
"While the academic community has demonstrated repeatedly that different racial or ethnic groups' cultural frames of reference and identity may play a role in affecting test scores, we have not used that knowledge to sufficiently advance testing processes," he said. "We sincerely hope that this research opens doors to thoughtful and important analysis that will allow us to legitimately assign scores that predict a job well done."
Revival of Test Bias Research in Preemployment Testing,"
Herman Aguinis, Steven A. Culpepper, Charles A. Pierce
Journal of Applied Psychology 2010, Vol. 95, No. 4, 648–680 DOI: 10.1037/a0018714
Link to JAP article [pdf]
Northumbria University (July 29, 2010)
Academics at Northumbria University have demonstrated a link between teenage binge drinking and damage to prospective memory.
Prospective memory is an important aspect of day-to-day memory function and is defined as the cognitive ability to remember to carry out an activity at some future point in time. Examples include remembering to attend an appointment at the dentist or to carry out a task such as remembering to pay a bill on time.
In the first study to examine the effects of binge drinking on prospective memory in teenagers, researchers tested the ability of fifty students from universities in North East England to remember a series of tasks. The students were shown a 10-minute video clip of a shopping district in Scarborough and were asked to remember to carry out a series of instructions when they saw specified locations.
Twenty-one of the students were categorized as binge drinkers. For women, this meant that they drank the equivalent of six standard glasses of wine or, for men, six pints of beer, two or more times a week. The remaining 29 participants were categorized as non-binge drinkers.
The study found that the binge drinkers recalled significantly fewer location-action/items combinations than their non-binging peers. These findings were observed after screening out teenagers who used other substances (such as ecstasy, cannabis and tobacco), those who had used alcohol within the last 48 hours, and after observing no between-group differences on age, anxiety and depression.
Dr Tom Heffernan led the study. He comments: "The mechanisms that may underlie such everyday cognitive impairments associated with binge drinking are not yet fully understood. It is possible that excessive drinking may interfere with the neuro-cognitive development of the teenage brain.
"It is important to realize that there no 'safe' levels of drinking set for teenagers and that the amount of bingeing revealed in the present study represents a high volume of alcohol intake across the two to three bingeing sessions which were the norm in the group. The high levels of drinking amongst teenagers is particularly worrying given the mounting evidence that the teenage brain is still maturing and undergoing significant development in terms of its structure and function.
"Given that teenagers are inexperienced drinkers who have both a low tolerance for alcohol and immature neuro-physiological systems, they should therefore be drinking much less than the 'safe' levels recommended for adults."
Intriguingly, one other finding of the study is that binge drinkers do not perceive themselves to have a poor memory, suggesting teenagers do not appreciate the damage that is being done.
Does binge drinking in teenagers affect their everyday prospective memory?
T. Heffernan, R. Clark, J. Bartholomew, J. Ling, S. Stephens.
Drug and Alcohol Dependence, 2010; 109 (1-3): 73 DOI: 10.1016/j.drugalcdep.2009.12.013
Link to DAD abstract
A new study from Perth's Telethon Institute for Child Health Research shows an association between ADHD and a 'Western-style' diet in adolescents.
Leader of Nutrition studies at the Institute, Associate Professor Wendy Oddy, said the study examined the dietary patterns of 1800 adolescents from the long-term Raine Study and classified diets into 'Healthy' or 'Western' patterns.
"We found a diet high in the Western pattern of foods was associated with more than double the risk of having an ADHD diagnosis compared with a diet low in the Western pattern, after adjusting for numerous other social and family influences," Dr Oddy said.
"We looked at the dietary patterns amongst the adolescents and compared the diet information against whether or not the adolescent had received a diagnosis of ADHD by the age of 14 years. In our study, 115 adolescents had been diagnosed with ADHD, 91 boys and 24 girls."
A "healthy" pattern is a diet high in fresh fruit and vegetables, whole grains and fish. It tends to be higher in omega-3 fatty acids, folate and fiber. A "Western" pattern is a diet with a trend towards takeaway foods, confectionary, processed, fried and refined foods. These diets tend to be higher in total fat, saturated fat, refined sugar and sodium.
"When we looked at specific foods, having an ADHD diagnosis was associated with a diet high in takeaway foods, processed meats, red meat, high fat dairy products and confectionary," Dr Oddy said.
"We suggest that a Western dietary pattern may indicate the adolescent has a less optimal fatty acid profile, whereas a diet higher in omega-3 fatty acids is thought to hold benefits for mental health and optimal brain function.
"It also may be that the Western dietary pattern doesn't provide enough essential micronutrients that are needed for brain function, particularly attention and concentration, or that a Western diet might contain more colors, flavors and additives that have been linked to an increase in ADHD symptoms. It may also be that impulsivity, which is a characteristic of ADHD, leads to poor dietary choices such as quick snacks when hungry."
Dr Oddy said that whilst this study suggests that diet may be implicated in ADHD, more research is needed to determine the nature of the relationship.
"This is a cross-sectional study so we cannot be sure whether a poor diet leads to ADHD or whether ADHD leads to poor dietary choices and cravings," Dr Oddy said.
ADHD Is Associated With a 'Western' Dietary Pattern in Adolescents.
Amber L. Howard, Monique Robinson, Grant J. Smith, Gina L. Ambrosini, Jan P. Piek, and Wendy H. Oddy
Journal of Attention Disorders, 2010; published on line before print DOI: 10.1177/1087054710365990
Link to JAD abstract
UCLA scientists have identified for the first time a cell-of-origin for human prostate cancer, a discovery that could result in better predictive and diagnostics tools and the development of new and more effective targeted treatments for the disease.
The researchers, from UCLA's Jonsson Comprehensive Cancer Center, proved that basal cells found in benign prostate tissue could become human prostate cancer in mice with suppressed immune systems, a finding that bucks conventional wisdom. It had been widely believed that luminal cells found in the prostate were the culprits behind prostate cancer because the resulting malignancies closely resembled luminal cells, said Dr. Owen Witte, a Jonsson Cancer Center member and director of the UCLA Broad Stem Cell Research Center.
"Certainly the dominant thought is that human prostate cancer arose from the luminal cells because the cancers had more features resembling luminal cells," said Witte, senior author of the study and a Howard Hughes Medical Institute Investigator. "But we were able to start with a basal cell and induce human prostate cancer and now, as we go forward, this gives us a place to look in understanding the sequence of genetic events that initiates prostate cancer and defining the cell signaling pathways that may be at work fueling the malignancy, helping us to potentially uncover new targets for therapy."
The researchers took healthy tissue from prostate biopsies and separated the cells based on their surface marker expression into groups of luminal cells and groups of basal cells. Using viral vectors as vehicles, they then expressed altered genes known to cause cancer into both cell populations and placed the cells in mice to see which developed cancer, said Andrew Goldstein, a UCLA graduate student and first author of the study.
"Because of the widespread belief that luminal cells were the root of human prostate cancer, it would have been those cells examined and targeted to treat the disease," said Goldstein. "This study tells us that basal cells play an important role in the prostate cancer development process and should be an additional focus of targeted therapies."
In normal prostate tissue, basal cells have a more stem cell-like function, Goldstein said, meaning they proliferate more to re-grow human prostate tissue. Luminal cells don't proliferate as much, but rather produce major proteins that are important for reproduction. Something is going awry in the basal cells that results in cancer and Witte and Goldstein plan to study those cells to uncover the mechanisms that result in malignancy.
Currently, there is a dearth of knowledge about how prostate cancer develops to treat it effectively in a targeted way, as Herceptin targets an out-of-control production of growth factor receptors in breast cancer cells. The major targeted therapy used for prostate cancer is directed at the androgen receptor and it is not always effective, Witte said.
The new human-in-mouse model system developed in the study -- created by taking healthy human prostate tissue that will induce cancer once it is placed in mice instead of taking malignant tissue that is already cancerous and implanting it -- can now be used to evaluate the effectiveness of new types of therapeutics. By using defined genetic events to activate specific signaling pathways, researchers can more easily compare therapeutic efficacy. The new model, by deconstructing tissue and then reconstructing it, also will aid in analyzing how the cells change during cancer progression.
"There are very few examples of taking benign cells and turning them into cancer experimentally," Goldstein said. "We usually study cancer cell lines created from malignant tumors. This study resulted in the creation of a novel model system that is highly adaptable, such that we can test any cellular pathway and its interactions with other genes known to induce cancer, and we can start with any type of cell as long as it can be reproducibly purified."
In this system, Witte and Goldstein know the "history" of the cells that became cancer, unlike the cancer cells lines used in other work.
"We know those cells are malignant, but we don't know how they got there," Goldstein said. "By starting with healthy cells and turning them into cancer, we can study the cancer development process. If we understand where the cancer comes from, we may be able to develop better predictive and diagnostic tools. If we had better predictive tools, we could look earlier in the process of cancer development and find markers that are better than the current PSA test at catching disease early, when it is more treatable."
Rising PSA levels can indicate the presence of cancer that is already developing in the prostate. However, now that it is known that basal cells are one root of human prostate cancers, scientists can study pre-malignant basal cells and uncover what they express that the healthy ones don't, perhaps revealing a new marker for early detection, Goldstein said. Also, a therapy directed at the pre-malignant basal cells about to become malignant could provide a way to prevent the cancer before it becomes dangerous.
This year alone, more than 217,000 men will be diagnosed with prostate cancer. Of those, more than 32,000 will die from their disease.
The study was funded by a Prostate Cancer Foundation Challenge Award, the Howard Hughes Medical Institute and the Department of Defense.
Identification of a Cell of Origin for Human Prostate Cancer.
Andrew S. Goldstein, Jiaoti Huang, Changyong Guo, Isla P. Garraway, and Owen N. Witte.
Science, 30 July 2010: Vol. 329. no. 5991, pp. 568 - 571. DOI: 10.1126/science.1189992
Link to Science abstract