College Park, MD, United States
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Ding N.,College Park | Simon J.Z.,College Park | Simon J.Z.,University of Maryland University College
Journal of Neurophysiology | Year: 2012

The cortical representation of the acoustic features of continuous speech is the foundation of speech perception. In this study, noninvasive mag-netoencephalography (MEG) recordings are obtained from human subjects actively listening to spoken narratives, in both simple and cocktail party-like auditory scenes. By modeling how acoustic features of speech are encoded in ongoing MEG activity as a spectro-temporal response function, we demonstrate that the slow temporal modulations of speech in a broad spectral region are represented bilaterally in auditory cortex by a phase-locked temporal code. For speech presented monaurally to either ear, this phase-locked response is always more faithful in the right hemisphere, but with a shorter latency in the hemisphere contralateral to the stimulated ear. When different spoken narratives are presented to each ear simultaneously (dichotic listening), the resulting cortical neural activity precisely encodes the acoustic features of both of the spoken narratives, but slightly weakened and delayed compared with the monaural response. Critically, the early sensory response to the attended speech is considerably stronger than that to the unattended speech, demonstrating top-down attentional gain control. This attentional gain is substantial even during the subjects' very first exposure to the speech mixture and therefore largely independent of knowledge of the speech content. Together, these findings characterize how the spectrotemporal features of speech are encoded in human auditory cortex and establish a single-trial-based paradigm to study the neural basis underlying the cocktail party phenomenon. © 2012 the American Physiological Society.

Becerra F.E.,U.S. National Institute of Standards and Technology | Fan J.,U.S. National Institute of Standards and Technology | Baumgartner G.,College Park | Goldhar J.,University of Maryland University College | And 2 more authors.
Nature Photonics | Year: 2013

Measurement of the state of a quantum system with inherent quantum uncertainty (noise) approaching the ultimate physical limits is of both technological and fundamental interest. Quantum noise prevents any mutually nonorthogonal quantum states, such as coherent states, from being distinguished with perfect accuracy. Optimized quantum measurements for nonorthogonal coherent states allow, in principle, for state discrimination sensitivities surpassing the standard quantum limit. Realizing quantum receivers that can detect multiple coherent states with sensitivity levels approaching the ultimate quantum limits is fundamental to quantum-enhanced measurements, and can optimize the performance of quantum and classical communications as well as future implementations of quantum technologies. Here, we demonstrate the first quantum receiver that unconditionally discriminates four nonorthogonal coherent states with error probabilities below the standard quantum limit. This receiver achieves error rates four times lower than is possible with any ideal conventional receiver with perfect detection efficiency. © 2013 Macmillan Publishers Limited. All rights reserved.

Feng P.C.H.,College Park | Reddy S.,U.S. Department of Agriculture
Applied and Environmental Microbiology | Year: 2013

Shiga-toxigenic Escherichia coli (STEC) strains were isolated from a variety of fresh produce, but mostly from spinach, with an estimated prevalence rate of 0.5%. A panel of 132 produce STEC strains were characterized for the presence of virulence and putative virulence factor genes and for Shiga toxin subtypes. About 9% of the isolates were found to have the eae gene, which encodes the intimin binding protein, and most of these belonged to known pathogenic STEC serotypes, such as O157:H7 and O26: H11, or to serotypes that reportedly have caused human illness. Among the eae-negative strains, there were three O113:H21 strains and one O91:H21 strain, which historically have been implicated in illness and therefore may be of concern as well. The ehxA gene, which encodes enterohemolysin, was found in ~60% of the isolates, and the saa and subAB genes, which encode STEC agglutinating adhesin and subtilase cytotoxin, respectively, were found in ~30% of the isolates. However, the precise roles of these three putative virulence factors in STEC pathogenesis have not yet been fully established. The stx1a and stx2a subtypes were present in 22% and 56%, respectively, of the strains overall and were the most common subtypes among produce STEC strains. The stx2d subtype was the second most common subtype (28% overall), followed by stx2c (7.5%), and only 2 to 3%of the produce STEC strains had the stx2e and stx2g subtypes. Almost half of the produce STEC strains had only partial serotypes or were untyped, and most of those that were identified belonged to unremarkable serotypes. Considering the uncertainties of some of these Stx subtypes and putative virulence factors in causing human illness, it is difficult to determine the health risk of many of these produce STEC strains. © 2013, American Society for Microbiology.

Soykal O.,College Park | Ruskov R.,College Park | Tahan C.,College Park
Physical Review Letters | Year: 2011

A quantum mechanical superposition of a long-lived, localized phonon and a matter excitation is described. We identify a realization in strained silicon: a low-lying donor transition (P or Li) driven solely by acoustic phonons at wavelengths where high-Q phonon cavities can be built. This phonon-matter resonance is shown to enter the strongly coupled regime where the "vacuum" Rabi frequency exceeds the spontaneous phonon emission into noncavity modes, phonon leakage from the cavity, and phonon anharmonicity and scattering. We introduce a micropillar distributed Bragg reflector Si/Ge cavity, where Q 105-106 and mode volumes V 25λ3 are reachable. These results indicate that single or many-body devices based on these systems are experimentally realizable. © 2011 American Physical Society.

Gaitan F.,College Park | Clark L.,Southern Illinois University Carbondale
Physical Review Letters | Year: 2012

The graph-theoretic Ramsey numbers are notoriously difficult to calculate. In fact, for the two-color Ramsey numbers R(m,n) with m, n≥3, only nine are currently known. We present a quantum algorithm for the computation of the Ramsey numbers R(m,n). We show how the computation of R(m,n) can be mapped to a combinatorial optimization problem whose solution can be found using adiabatic quantum evolution. We numerically simulate this adiabatic quantum algorithm and show that it correctly determines the Ramsey numbers R(3,3) and R(2,s) for 5≤s≤7. We then discuss the algorithm's experimental implementation, and close by showing that Ramsey number computation belongs to the quantum complexity class quantum Merlin Arthur. © 2012 American Physical Society.

Gaitan F.,College Park | Clark L.,Southern Illinois University Carbondale
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2014

In the graph isomorphism (GI) problem two N-vertex graphs G and G′ are given and the task is to determine whether there exists a permutation of the vertices of G that preserves adjacency and transforms G→G′. If yes, then G and G′ are said to be isomorphic; otherwise they are nonisomorphic. The GI problem is an important problem in computer science and is thought to be of comparable difficulty to integer factorization. In this paper we present a quantum algorithm that solves arbitrary instances of GI and which also provides an approach to determining all automorphisms of a given graph. We show how the GI problem can be converted to a combinatorial optimization problem that can be solved using adiabatic quantum evolution. We numerically simulate the algorithm's quantum dynamics and show that it correctly (i) distinguishes nonisomorphic graphs; (ii) recognizes isomorphic graphs and determines the permutation(s) that connect them; and (iii) finds the automorphism group of a given graph G. We then discuss the GI quantum algorithm's experimental implementation, and close by showing how it can be leveraged to give a quantum algorithm that solves arbitrary instances of the NP-complete subgraph isomorphism problem. The computational complexity of an adiabatic quantum algorithm is largely determined by the minimum energy gap Δ(N) separating the ground and first-excited states in the limit of large problem size N1. Calculating Δ(N) in this limit is a fundamental open problem in adiabatic quantum computing, and so it is not possible to determine the computational complexity of adiabatic quantum algorithms in general, nor consequently, of the specific adiabatic quantum algorithms presented here. Adiabatic quantum computing has been shown to be equivalent to the circuit model of quantum computing, and so development of adiabatic quantum algorithms continues to be of great interest. © 2014 American Physical Society.

Lands B.,College Park
Prostaglandins and Other Lipid Mediators | Year: 2011

If people stay healthy, less health care treatments need to be paid. Alternatively, health care treatments are uneconomical and unethical when they only remove signs and symptoms and leave the primary cause neglected and unchanged to cause future harm. Neglected preventable causes continue to cause massive health-related financial loss in the US. Monitoring imbalances of omega-3 and omega-6 hormone precursors in individuals can increase awareness and motivation for making efforts to prevent this pervasive diet-related cause of dysfunction, disease and financial loss. We now have low-cost tools for individuals to monitor their balance of omega-3 and omega-6 hormone precursors and to identify and choose foods that will maintain a desired balance and a desired quality of life. © 2011 Elsevier Inc. All rights reserved.

A summary of an examination of studies of interlaboratory reproducibility of measurements for detecting the presence of microorganisms in food products is presented. In such studies multiple laboratories, 10 or more, compare the performances of reference and test methods at the limit of detection of the methods that is at spiking levels around 1 cfu per analytical portion. A laboratory's performance is expressed as the number of positive replicates detected per set of six. The data only imply the presence or absence of significant between-laboratory effects with the test method relative to the reference method. It is difficult to parse the observed variability into the contributions of the sample variability and between-laboratory effects. This is because at spiking levels close to 1 cfu per portion it cannot be assured that laboratories are examining portions with equivalent numbers of the target microbe. In this study published data are reformulated to the number of laboratories observing a given number of positive results per replicate set in order to reflect the inhomogeneity of the spike distribution in the replicate portions. A mean spiking level that is less uncertain than the reported 3-tube reference method MPN value is estimated from the pooled proportions of positives that the laboratories obtained with the reference method. The expected distribution of the spike was calculated from its mean value using the binomial equation. The numerical distributions of the laboratories among the 7 possible positive categories (0-6 positives per replicate set) were statistically indistinguishable from the expected binomial distribution thus corroborating this approach. Probable instances of interlaboratory performance differences were detected by further statistical analysis. This analytical approach, as well as transparently reflecting the sampling variability, also suggested ways of improving and simplifying such studies. © 2011.

Lands B.,College Park
Progress in Lipid Research | Year: 2014

Current public advice from the Food and Nutrition Board (FNB) about essential fatty acids (EFA) has limited quantitative details about three processes: (1) similar dynamics for n-3 linolenic and n-6 linoleic polyunsaturated fatty acids (PUFA) in maintaining 20- and 22-carbon n-3 and n-6 highly unsaturated fatty acids (HUFA) in tissues; (2) different dynamics for tissue n-3 and n-6 HUFA during formation and action of hormone-like eicosanoids; (3) simultaneous formation of non-esterified fatty acids (NEFA) and low density lipoprotein (LDL) from very low density lipoprotein (VLDL) formed from excess food energy and secreted by the liver. This report reviews evidence that public health may benefit from advice to eat less n-6 nutrients, more n-3 nutrients and fewer calories per meal. Explicit data for linoleic acid fit an Estimated Average Requirement (EAR) near 0.1 percent of daily food energy (en%) meeting needs of half the individuals in a group, a Recommended Dietary Allowance (RDA) near 0.5 en% meeting needs of 97-98 percent of individuals, and a Tolerable Upper Intake Level (UL) near 2 en% having no likely risk of adverse health effects. Quantitative tools help design and monitor explicit interventions that could beneficially replace imprecise advice on "healthy foods" with explicit preventive nutrition. © 2014 Elsevier Ltd. Published by Elsevier Ltd.

Lands B.,College Park
Nutrients | Year: 2012

Essential fatty acids (EFA) are nutrients that form an amazingly large array of bioactive mediators that act on a large family of selective receptors. Nearly every cell and tissue in the human body expresses at least one of these receptors, allowing EFA-based signaling to influence nearly every aspect of human physiology. In this way, the health consequences of specific gene-environment interactions with these nutrients are more extensive than often recognized. The metabolic transformations have similar competitive dynamics for the n-3 and n-6 homologs when converting dietary EFA from the external environment of foods into the highly unsaturated fatty acid (HUFA) esters that accumulate in the internal environment of cells and tissues. In contrast, the formation and action of bioactive mediators during tissue responses to stimuli tend to selectively create more intense consequences for n-6 than n-3 homologs. Both n-3 and n-6 nutrients have beneficial actions, but many common health disorders are undesired consequences of excessive actions of tissue n-6 HUFA which are preventable. This review considers the possibility of preventing imbalances in dietary n-3 and n-6 nutrients with informed voluntary food choices. That action may prevent the unintended consequences that come from eating imbalanced diets which support excessive chronic actions of n-6 mediators that harm human health. The consequences from preventing n-3 and n-6 nutrient imbalances on a nationwide scale may be very large, and they need careful evaluation and implementation to avoid further harmful consequences for the national economy. © 2012 by the authors; licensee MDPI, Basel, Switzerland.

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