bluuebunny/crossref_metadata_2025 huggingface dataset:
International Team Examines Health in Zones Contaminated by Chernobyl
Authors: Levi Barbara Goss
Published: January 2008

Glasnost notwithstanding, the Soviet Union has faced a credibility gap regarding its public pronouncements about the health effects from the explosion of a nuclear reactor at the Chernobyl atomic power station in 1986. While rumors have abounded in the affected republics of excess cancers or thyroid abnormalities, the central government has not found any clear evidence for maladies attributable to the accident. (See PHYSICS TODAY, July 1990, page 62.) In October 1989, the Soviets asked the International Atomic Energy Agency to review government assessments of the radiological and health situation in the areas affected by the accident and to evaluate measures to protect the population. The resulting report, released at the end of May, largely validates the Soviet assessments to date. The study team did not find any significant health abnormalities that might be associated with radiological exposures except for high levels of stress and anxiety caused by concern over the radiation. Because of the limited scope of the study and the long latency period of cancers, the team could not determine whether there are any excess cancers in the populations examined. The report contains some recommendations for improvements in the ongoing assessments.
A New Generation of Gamma Detectors for Nuclear Physics
Authors: Schwarzschild Bertram
Published: January 2008

The construction of Gammasphere, an important new photon detector for nuclear physics, began last month at the Lawrence Berkeley Laboratory. The principal purpose of this $20 million spherical array of germanium and bismuth germanate crystals will be to measure simultaneously the energies of as many as half a dozen gammas from the step-by-step deexcitation of a single excited nucleus.
Production of a slit skimmer for use in cold supersonic molecular beams
Authors: Subramanian Ranga , Sulkes Mark
Published: January 2008

Cold molecular beams generated by skimming pulsed supersonic gas expansions normally employ conical skimmers. The use of slit shaped skimmers instead of conical skimmers can afford significant signal enhancements. At this time, however, slit shaped skimmers are not available commercially. We describe a straightforward method for producing functional slit skimmers.
Entropy-energy decomposition from nonequilibrium work trajectories
Authors: Nummela Jeremiah , Yassin Faten , Andricioaei Ioan
Published: January 2008

We derive expressions for the equilibrium entropy and energy changes in the context of the Jarzynski equality relating nonequilibrium work to equilibrium free energy. The derivation is based on a stochastic path integral technique that reweights paths at different temperatures. Stochastic dynamics generated by either a Langevin equation or a Metropolis Monte Carlo scheme are treated. The approach enables the entropy-energy decomposition from trajectories evolving at a single-temperature and does not require simulations or measurements at two or more temperatures. Both finite difference and analytical formulae are derived. Testing is performed on a prototypical model system and the method is compared with existing thermodynamic integration and thermodynamic perturbation approaches for entropy-energy decomposition. The new formulae are also put in the context of more general, dynamics-independent expressions that derive from either a fluctuation theorem or the Feynman–Kac theorem.
Ambipolar transistor behavior in p-doped InAs nanowires grown by molecular beam epitaxy
Authors: Sørensen B. S. , Aagesen M. , Sørensen C. B. , Lindelof P. E. , Martinez K. L. , Nygård J.
Published: January 2008

We present the electric properties of p-InAs nanowire field-effect transistors showing ambipolar conduction. Be doped nanowires are grown by the vapor-solid-solid mechanism using molecular beam epitaxy with in situ deposited Au catalyst particles. P-type conduction in InAs nanowires is challenging because of the Fermi-level pinning above the conduction band edge at the nanowire surface that leads to creation of an electron inversion layer. We demonstrate that this task is possible without a modified surface and report a strong temperature dependence (10–105) of the on-off ratio caused by the surface inversion layer.
Infrared spectroscopy of gas phase C3H5+: The allyl and 2-propenyl cations
Authors: Douberly Gary E. , Ricks Allen M. , Schleyer Paul v. R. , Duncan Michael A.
Published: January 2008

C 3 H 5 + cations are probed with infrared photodissociation spectroscopy in the 800–3500cm−1 region using the method of rare gas tagging. The ions and their complexes with Ar or N2 are produced in a pulsed electric discharge supersonic expansion cluster source. Two structural isomers are characterized, namely, the allyl (CH2CHCH2+) and 2-propenyl (CH3CCH2+) cations. The infrared spectrum of the allyl cation confirms previous theoretical and condensed phase studies of the C2v charge delocalized, resonance-stabilized structure. The 2-propenyl cation spectrum is consistent with a Cs symmetry structure having a nearly linear CCC backbone and a hyperconjugatively stabilizing methyl group.
Optical switching based on high-speed phased array optical beam steering
Authors: Jarrahi Mona , Pease R. Fabian W. , Miller David A. B. , Lee Thomas H.
Published: January 2008

We present a high-speed optical switching scheme based on phased array optical beam steering, and analyze the trade-off between the switch power efficiency, signal-to-noise-ratio, number of output channels, and switching speed. For the proof of concept, a two-channel optical switch has been fabricated, using a high-speed GaAs∕AlGaAs multiple quantum well phase modulator. We demonstrate a beam deflection angle of 100mrad at the fastest ever reported speed of 18GHz, consuming 1.8mW. A signal-to-noise ratio of 8dB is measured at each output channel. The relatively low signal-to-noise ratio can be further improved by increasing the number of phased arrays.
Ferromagnetism in pseudocubic BaFeO3 epitaxial films
Authors: Callender C. , Norton D. P. , Das R. , Hebard A. F. , Budai J. D.
Published: January 2008

Growth and properties of epitaxial BaFeO3 thin films in the metastable cubic perovskite phase are examined. BaFeO3 films were grown on (012) LaAlO3 and (001) SrTiO3 single crystal substrates by pulsed-laser deposition. X-ray diffraction shows that films grown between 650 and 850°C yield an oxygen-deficient BaFeO2.5+x pseudocubic perovskite phase that decreases in lattice spacing with increasing growth temperature. Magnetization measurements on as-deposited BaFeO3 films indicate weakly ferromagnetic behavior. Annealing in 1atm oxygen ambient converts them into conductive and robustly ferromagnetic pseudocubic BaFeO3 phase with TC=235K. Observation of ferromagnetism with increasing oxygen content is consistent with superexchange coupling of Fe+4–O–Fe+4.
Quantum dots formed in a GaAs∕AlGaAs quantum ring
Authors: Mühle A. , Wegscheider W. , Haug R. J.
Published: January 2008

We demonstrate the tunability of a GaAs∕AlGaAs quantum ring showing coherent Aharonov-Bohm oscillations up to a gate voltage regime where the ring splits into three quantum dots. This is explained based on the structure’s special confinement potential. We characterized the dots by analyzing the corresponding sets of Coulomb blockade lines. Additionally, the spatial configuration of the dots was confirmed by charge measurements using an adjacent quantum point contact.
An Evolving Physical System: The State of the American Physical Society
Authors: Merzbacher Eugen
Published: January 2008

Among all the terms that we use casually in talking about physics, without feeling the need to define or explicate them, the winner of the Citation Derby is probably the word “system.” Explicitly or by implication, the “physical system” defines the context in every class we teach, every seminar we give, every paper we write. Talking about physics without specifying the system is a vacuous exercise, and we exhort our students from the first day to think clearly about the system under consideration—what it includes and what it does not include, its relevant characteristics, its observable aspects, its degrees of freedom and its response to external influences and perturbations.
Testing Physics Achievement: Trends Over Time and Place
Authors: Pfeiffenberger Will , Zolandz Ann Marie , Jones Lee
Published: January 2008

A physicist concerned with pre-college physics curriculums may inquire how students in the United States today compare not only with those in the past, but also with those in other countries. He or she may also wonder how changes in high school and college physics curriculums affect testing methods and students' performance on standardized tests. Data from national physics testing programs sponsored by the College Board and the National Assessment of Educational Progress and from two international assessments of science achievement provide some insight into the answers to these questions.
Learning and Instruction in Pre-College Physical Science
Authors: Mestre Jose P.
Published: January 2008

Two main instructional practices are found in American education: One is prevalent, while the other is emerging. We have all experienced the prevalent practice, which results from the so-called transmission model of instruction. In this model, students are exposed to content through lectures, presentations and readings, and are expected to absorb the transmitted knowledge in ready-to-use form. Although it is not a model of learning per se, the transmission model does make a pivotal assumption about learning, namely that the message the student receives is the message the teacher intended. Within this model, students' difficulties in grasping a concept are interpreted as indications that the presentation was not clear or forceful enough to be understood (that is, the signal being transmitted was either weak or garbled). Thus many users of the transmission model believe that if they make the presentation more lucid or persistent—for example, by transmitting at a slower speed or in a louder voice—students will eventually understand. Too often we are inclined to believe that by speaking in shorter words and sentences we can teach the big ideas in relativity to ninthgraders; this is simply not the case if the students' intellectual development is not at a level where they can appreciate the subtleties of difficult concepts.
Calculus-Based Physics Without Lectures
Authors: Laws Priscilla W.
Published: January 2008

Every fall several hundred thousand students enroll in calculus-based “engineering” physics courses throughout the United States. Informal statistics tell us that over half of them will fail to complete the sequence of introductory courses. These students complain that physics is hard and boring. The most compelling student critique of traditional introductory physics and chemistry courses comes from college graduates in the humanities who were engaged by Sheila Tobias to take introductory science for credit. These students paint a devastating portrait of introductory courses as uninteresting, time consuming, narrowly fixated on the procedures of textbook problem solving, devoid of peer cooperation, lacking in student involvement during lectures, crammed with too much material, and biased away from conceptual understanding.
Their Most Productive Years: Young Physics Faculty in 1990
Authors: Czujko Roman , Kleppner Daniel , Rice Stuart A.
Published: January 2008

We live in a society shaped by science and technology. As our society evolves it will draw more and more upon science and technology to generate economic growth, to improve health and to enhance the quality of life. In order to provide adequate scientific and engineering personnel for our national needs and to sustain the knowledge base from which growth derives, careers in science and engineering must be attractive to our youth.
Unity in the Science of Physics
Authors: Krumhansl James A.
Published: January 2008

I hope that this special celebratory session will become an annual custom at our large conferences—to take time out to survey both the diversity and unity of physics in a common meeting that is undiluted by the multiplicity of parallel sessions that have become the hallmark of our gatherings. Our research endeavors span a wide spectrum of physics, but at the core of every effort is a common creed: to push to the frontiers our understanding of natural phenomena, by measurement and theoretical analysis. In this article, in addition to giving the retiring president's report, I want to address the idea of whether one can identify sources of unity in the science of physics. My remarks may complement those of one of my predecessors and colleagues, Robert R. Wilson, in his 1985 retiring presidential address, “The Sentiment of the Unity of Physics” (PHYSICS TODAY, July 1986, page 26).
The Decade of Infrared Astronomy
Authors: Gillett Frederick C. , Houck James R.
Published: January 2008

The enormous technological and scientific advances of the 1980s give us an unparalleled opportunity to address fundamental issues in astrophysics through observations at infrared wavelengths. The recommendations of the Astronomy and Astrophysics Survey Committee reflect these opportunities for research in the 1–1000-micron wavelength range. The highest priority recommendations for large new projects in this part of the spectrum are for a Space Infrared Telescope Facility, or SIRTF, and an 8-meter ground-based Infrared Optimized Telescope, or IRO. A Stratospheric Observatory for Infrared Astronomy, or SOFIA, is a highly recommended medium-sized initiative, and there are strong recommendations for several other infrared initiatives.
Particle Astrophysics
Authors: Sadouler Bernard , Cronin James W.
Published: January 2008

Particle astrophysics emerged in the 1980s as a new field at the junction of high-energy astrophysics, cosmology and particle physics. This new experimental, observational and theoretical discipline concerns itself, for example, with the nature of dark matter; the detection of neutrinos from the Sun and from supernovae; the evidence for powerful acceleration mechanisms in the vicinity of neutron stars; and the suggestion that quantum fluctuation and topological singularities in the first moments of the cosmos played a role in the formation of the great structures we see today stretching over hundreds of millions of light-years.
Unification of Couplings
Authors: Dimopoulos Savas , Raby Stuart A. , Wilczek Frank
Published: January 2008

Ambitious attempts to obtain a unified description of all the interactions of nature have so far been more notable for their ingenuity, beauty and chutzpah than for any help they have afforded toward understanding concrete facts about the physical world. In this article we wish to describe one shining exception: how ideas about the unification of the strong, weak and electromagnetic interactions lead to concrete, quantitative predictions about the relative strengths of these interactions.
Decoherence and the Transition from Quantum to Classical
Authors: Zurek Wojciech H.
Published: January 2008

Quantum mechanics works exceedingly well in all practical applications. No example of conflict between its predictions and experiment is known. Without quantum physics we could not explain the behavior of solids, the structure and function of DNA, the color of the stars, the action of lasers or the properties of superfluids. Yet well over half a century after its inception, the debate about the relation of quantum mechanics to the familiar physical world continues. How can a theory that can account ith precision for everything we can measure still be deemed lacking?
Through a Beer Glass Darkly
Authors: Shafer Neil E. , Zare Richard N.
Published: January 2008

Pour yourself a glass of beer and look closely at the rising bubbles. Careful examination shows that they are seldom distributed uniformly throughout the liquid. Instead, streams of bubbles appear to rise from certain spots on the surface of the glass. Closer inspection reveals that the bubbles rapidly grow in size as they ascend, the volume of each bubble often doubling or more by the time it reaches the top of the glass. In addition, the speed of the bubbles increases as they travel upward.
Taylor-Couette Flow: The Early Days
Authors: Donnelly Russell J.
Published: January 2008

The striking flow shown in figure 1 is produced in a simple apparatus: A fluid is confined between two concentric cylinders, with the inner and perhaps the outer cylinder able to rotate. The cellular motion that develops with rotation was discovered and described mathematically by Geoffrey I. Taylor in 1923. A similar apparatus, with the inner cylinder suspended from a torsion fiber and the outer cylinder rotating, was used even earlier as a viscometer. Maurice Couette described this arrangement in his thesis, which he presented in Paris in 1890. For this reason, modern investigators refer to flow between rotating cylinders as Taylor-Couette flow. In this article I trace the beginnings of the subject back to Isaac Newton and, by discussing the contributions of Newton, George Stokes, Max Margules, Arnulph Mallock, Couette, Taylor, S. Chandrasekhar and others, show how the study of this flow evolved to its place of prominence today.
Shaping the Future: Science and Technology 2030
Authors: Rhodes Frank H. T.
Published: January 2008

In observing its 40th anniversry last year, the National Science Foundation held a special symposium to celebrate its achievements and to look ahead to the next 40 years for the foundation as well as for all of science and technology in America. NSF's accomplishments are impressive. These include a major role in producing successive generations of scientists and engineers; in supporting pace-setting research in a multitude of fields, including some, such as high-temperature superconductivity, that it did much to initiate; and in monitoring the pulse of the nation's science and engineering enterprise.
High-Temperature Superconductivity
Authors: Rowell John
Published: January 2008

One can argue that superconductivity in “the oxides” was discovered in 1964, 1986 or 1987, depending on which oxide is chosen: the first to show superconductivity at any temperature, the first with a Tc greater than 20 K or the first with a Tc greater than 77 K. For many of us in the field, the time we remember is probably early December 1986, when experimenters from the University of Tokyo announced at the Materials Research Society meeting in Boston that they had confirmed the earlier findings of Georg Bednorz and Alex Müller at IBM in Zurich. There followed a frenetic period of a year or so that was unique in the history of science, with the American Physical Society meeting of March 1987 representing its peak of intensity (or hype, depending on one's point of view), although a close second must have been the Washington gathering where President Reagan gave the plenary talk.
Defects and Superconductivity in the Copper Oxides
Authors: Jorgensen James D.
Published: January 2008

Few superconducting materials have presented us with the structural elegance and complexity displayed by the recently discovered high-Tc copper oxides. The structures of these materials, consisting of metal-oxygen layers stacked in a variety of sequences, with the metal atoms often in unusual coordinations, are interesting in their own right. More importantly, our present understanding of the properties of the oxide superconductors depends heavily on a knowledge of their structures.
Critical Currents and Magnet Applications of High-Tc Superconductors
Authors: Larbalesrier David
Published: January 2008

The discovery of a 92 K superconductor in early 1987 by M. K. Wu, Paul Chu and their coworkers at the Universities of Alabama and Houston produced widespread euphoria. Newspapers and magazines of every conceivable political and social persuasion speculated on the applications of superconductivity. Some even foretold a new age; after the stone, bronze, iron, steel and semiconductor ages would come the superconductor age. Most of the applications envisaged for this new age depended on the generation of strong magnetic fields, frequently in large volumes. Thus the vanishing of resistance in the superconducting state was the key property for these applications, and it is this ability to carry very large current densities without ohmic loss that forms the essential thread of this article.
Manipulating and understanding antibiotic production in
Streptomyces coelicolor
A3(2) with decoy oligonucleotides
Authors: McArthur Michael , Bibb Mervyn J.
Published: January 2008

We have adapted and extended the decoy oligonucleotide technique for use in prokaryotes. To identify
cis
-acting regulatory elements within a promoter, we developed a DNase I/T7 exonuclease footprinting technique and applied it to
act
II-orf4 from
Streptomyces coelicolor
A3(2), which encodes the pathway-specific activator for production of the antibiotic actinorhodin. Our
in vivo
mapping data allowed us to create decoy oligonucleotides incorporating the identified regulatory elements and to test whether their introduction into
S. coelicolor
affected antibiotic production. We mapped the promoter region when in a transcriptionally inactive state before the onset of actinorhodin production with the aim of designing decoy oligonucleotides capable of interfering with potential repressor binding and so stimulate actinorhodin production. Mapping identified five candidates for decoy oligonucleotides, and these were tested in a plate-based assay to rapidly validate their activity. A transfection protocol was developed for liquid cultures that enabled efficient uptake of decoys, and quantitative real-time PCR demonstrated decoy persistence for >70 h. Measurement of the effects on growth, expression of
act
II-orf4, and antibiotic production demonstrated that one of the decoys, in concordance with the plate assay, was more efficacious than the others in increasing actinorhodin production. Two of the identified regulatory elements occurred upstream of gene SCO5812, deletion of which reduced actinorhodin production, confirming that experimental analysis of regulatory motifs can provide new insights into factors influencing antibiotic production in streptomycetes.
The Progression of Inflammation Parallels the Dermal Angiogenesis in a Keratin 14 IL‐4‐Transgenic Model of Atopic Dermatitis
Authors: Chen Lin , Marble Deborah J. , Agha Rania , Peterson Jennifer D. , Becker Robert P. , Jin Tianquan , Li Jianxun , Chan Lawrence S.
Published: January 2008

The role angiogenesis plays in atopic dermatitis is not well understood. The authors previously demonstrated ultrastructurally dermal microvascular angiogenesis in the IL‐4‐transgenic mouse model of atopic dermatitis. Here, they determine the angiogenic factors involved in dermal microvascular angiogenesis, regulatory function of inflammatory cytokines on the VEGF‐A production, and microvascular permeability in this model. Computer‐assisted photometric analyses for immunofluorescence‐labeled CD31 demonstrated a progressive increase in blood vessel number, diameter, and percent dermal areas occupied by CD31+ vessels as the disease evolves in transgenic mice from before disease onset through early and late skin lesions. Similar findings were documented for VEGR2+ vessels. Quantification of skin angiogenic factor mRNAs showed progressive increase of transcripts of VEGF‐A, but not VEGF‐B, VEGF‐C, or VEGF‐D. ELISA showed a similar increase of VEGF‐A in the serum and skin of transgenic mice. IL‐6 and IFN‐γ stimulated VEGF‐A mRNA production in the skin and in primary keratinocytes of transgenic mice. Other skin angiogenic factors that increased included Ang‐1, Ang‐2, GBP‐1, and VE‐cadherin. Microvascular leakage began in the transgenic mouse skin before disease onset and peaked in the late stage. In conclusion, IL‐6 and IFN‐γ may play important roles in upregulation of VEGF‐A, along with other pro‐angiogenic factors, to induce dermal microvascular angiogenesis.
Estimation of Apparent Tumor Vascular Permeability from Multiphoton Fluorescence Microscopic Images of P22 Rat Sarcomas In Vivo
Authors: Reyes‐Aldasoro Constantino Carlos , Wilson Ian , Prise Vivien E. , Barber Paul R. , Ameer‐Beg M. , Vojnovic Borivoj , Cunningham Vincent J. , Tozer Gillian M.
Published: January 2008

Objective: To develop an image processing‐based method to quantify the rate of extravasation of fluorescent contrast agents from tumor microvessels, and to investigate the effect of the tumor vascular disrupting agent combretastatin A‐4‐P (CA‐4‐P) on apparent tumor vascular permeability to 40 kDa fluorescein isothiocyanate (FITC) labeled dextran.

Methods: Extravasation of FITC‐dextran was imaged in 3 dimensions over time within P22 sarcomas growing in dorsal skin flap “window chambers” in BDIX rats using multiphoton fluorescence microscopy. Image processing techniques were used to segment the data into intra‐ and extravascular regions or classes. Quantitative estimates of the tissue influx (vascular leakage) rate constant, Ki, were obtained from the time courses of the fluorescence intensities in the two classes. Apparent permeability, P, was calculated, assuming Ki = PS/V, where S is vascular surface area in tumor volume V.

Results: Combining image processing and kinetic analysis algorithms with multiphoton fluorescence microscopy enabled quantification of the rate of tumor vascular leakage, averaged over a large number of vessels. Treatment with CA‐4‐P caused a significant increase in Ki from 1.13 ± 0.33 to 2.59 ± 0.20 (s−1× 10−4; mean ± SEM), equivalent to an increase in P from 12.76 ± 3.36 to 30.94 ± 2.64 (cm s−1× 10−7).

Conclusions: A methodology was developed that provided evidence for a CA‐4‐P‐induced increase in tumor macromolecular vascular permeability, likely to be central to its anti‐cancer activity.
Effect of spatial distribution of T-Cells and HIV load on HIV progression
Authors: Graziano Frank M. , Kettoola Samira Y. , Munshower Judy M. , Stapleton Jack T. , Towfic George J.
Published: January 2008

Motivation: We present a spatial-temporal (ST) human immunodeficiency virus (HIV) simulation model to investigate the spatial distribution of viral load and T-cells during HIV progression. The proposed model uses the Finite Element (FE) method to divide a considered infected region into interconnected subregions each containing viral population and T-cells. HIV T-cells and viral load are traced and counted within and between subregions to estimate their effect upon neighboring regions. The objective is to estimate overall ST changes of HIV progression and to study the ST therapeutic effect upon HIV dynamics in spatial and temporal domains. We introduce sub-regional (spatial) parameters of T-cells and viral load production and elimination to estimate the spatial propagation and interaction of HIV dynamics under the influence of a 3TC D4T Reverse Transcriptase Inhibitors (RTI) drug regimen.

Results: In terms of percentage change standard deviation, we show that the average rate per 10 weeks (throughout a 10-year clinical trial) of the ST CD4+ change is 5.35% 1.3 different than that of the CD4+ rate of change in laboratory datasets, and the average rate of change of the ST CD8+ is 4.98% 1.93 different than that of the CD8+ rate of change. The half-life of the ST CD4+ count is 1.68% 3.381 different than the actual half-life of the CD4+ count obtained from laboratory datasets. The distribution of the viral load and T-cells in a considered region tends to cluster during the HIV progression once a threshold of 86–89% viral accumulation is reached.

Availability: Executable code and data libraries are available by contacting the corresponding author.

Implementation: C++ and Java have been used to simulate the suggested model. A Pentium III or higher platform is recommended.

Contact:  george.towfic@clarke.edu

Supplementary information: Supplementary data are available at Bioinformatics online.
OutlierD: an R package for outlier detection using quantile regression on mass spectrometry data
Authors: Cho HyungJun , Kim Yang-jin , Jung Hee Jung , Lee Sang-Won , Lee Jae Won
Published: January 2008

Summary: It is important to preprocess high-throughput data generated from mass spectrometry experiments in order to obtain a successful proteomics analysis. Outlier detection is an important preprocessing step. A naive outlier detection approach may miss many true outliers and instead select many non-outliers because of the heterogeneity of the variability observed commonly in high-throughput data. Because of this issue, we developed a outlier detection software program accounting for the heterogeneous variability by utilizing linear, non-linear and non-parametric quantile regression techniques. Our program was developed using the R computer language. As a consequence, it can be used interactively and conveniently in the R environment.

Availability: An R package, OutlierD, is available at the Bioconductor project at http://www.bioconductor.org

Contact:  jael@korea.ac.kr

Supplementary information: Supplementary Data are available at Bioinformatics online.
Glutamate receptor‐dependent increments in lactate, glucose and oxygen metabolism evoked in rat cerebellum in vivo
Authors: Caesar Kirsten , Hashemi Parastoo , Douhou Aicha , Bonvento Gilles , Boutelle Martyn G. , Walls Anne B. , Lauritzen Martin
Published: January 2008

Neuronal activity is tightly coupled with brain energy metabolism. Numerous studies have suggested that lactate is equally important as an energy substrate for neurons as glucose. Lactate production is reportedly triggered by glutamate uptake, and independent of glutamate receptor activation. Here we show that climbing fibre stimulation of cerebellar Purkinje cells increased extracellular lactate by 30% within 30 s of stimulation, but not for briefer stimulation periods. To explore whether lactate production was controlled by pre‐ or postsynaptic events we silenced AMPA receptors with CNQX. This blocked all evoked rises in postsynaptic activity, blood flow, and glucose and oxygen consumption. CNQX also abolished rises in lactate concomitantly with marked reduction in postsynaptic currents. Rises in lactate were unaffected by inhibition of glycogen phosphorylase, suggesting that lactate production was independent of glycogen breakdown. Stimulated lactate production in cerebellum is derived directly from glucose uptake, and coupled to neuronal activity via AMPA receptor activation.
Inconvenient Truths about neural processing in primary motor cortex
Authors: Scott Stephen H.
Published: January 2008

Primary motor cortex (MI) plays an important role in voluntary motor behaviour, yet considerable debate remains on how neural processing within this brain region contributes to motor function. This article provides a brief review of the dominant conceptual frameworks used to interpret MI activity, notably servo‐control during the 1970s and early 1980s, and sensorimotor transformations since that time. The former emphasized the use of feedback, but was abandoned because delays in sensory feedback could not permit sufficient feedback gains to generate observed patterns of limb movement. The latter framework focuses attention on identifying what coordinate frames, or representations, best describe neural processing in MI. However, studies have shown that MI activity correlates with a broad range of parameters of motor performance from spatial target location, hand or joint motion, joint torque and muscle activation patterns. Further, these representations can change across behaviours, such as from posture to movement. What do heterogeneous, labile neural representations mean and how do they help us understand how MI is involved in volitional motor control? Perhaps what is required is a new conceptual framework that re‐focuses the experimental problem back on processes of control. Specifically, optimal feedback control has been proposed as a theory of the volitional motor system and it is argued here that it provides a rich, new perspective for addressing the role of MI and other brain regions in volitional motor control.
Voltage‐gated sodium channels in nociceptive versus non‐nociceptive nodose vagal sensory neurons innervating guinea pig lungs
Authors: Kwong Kevin , Carr Michael J. , Gibbard Anna , Savage Tony J. , Singh Kuljit , Jing Junping , Meeker Sonya , Undem Bradley J.
Published: January 2008

Lung vagal sensory fibres are broadly categorized as C fibres (nociceptors) and A fibres (non‐nociceptive; rapidly and slowly adapting low‐threshold stretch receptors). These afferent fibre types differ in degree of myelination, conduction velocity, neuropeptide content, sensitivity to chemical and mechanical stimuli, as well as evoked reflex responses. Recent studies in nociceptive fibres of the somatosensory system indicated that the tetrodotoxin‐resistant (TTX‐R) voltage‐gated sodium channels (VGSC) are preferentially expressed in the nociceptive fibres of the somatosensory system (dorsal root ganglia). Whereas TTX‐R sodium currents have been documented in lung vagal sensory nerves fibres, a rigorous comparison of their expression in nociceptive versus non‐nociceptive vagal sensory neurons has not been carried out. Using multiple approaches including patch clamp electrophysiology, immunohistochemistry, and single‐cell gene expression analysis in the guinea pig, we obtained data supporting the hypothesis that the TTX‐R sodium currents are similarly distributed between nodose ganglion A‐fibres and C‐fibres innervating the lung. Moreover, mRNA and immunoreactivity for the TTX‐R VGSC molecules NaV1.8 and NaV1.9 were present in nearly all neurons. We conclude that contrary to findings in the somatosensory neurons, TTX‐R VGSCs are not preferentially expressed in the nociceptive C‐fibre population innervating the lungs.
Electrical remodelling maintains firing properties in cortical pyramidal neurons lackingKCND2‐encoded A‐type K+currents
Authors: Nerbonne Jeanne M. , Gerber Benjamin R. , Norris Aaron , Burkhalter Andreas
Published: January 2008

Considerable experimental evidence has accumulated demonstrating a role for voltage‐gated K+(Kv) channel pore‐forming (α) subunits of the Kv4 subfamily in the generation of fast transient outward K+,IA, channels. Immunohistochemical data suggest thatIAchannels in hippocampal and cortical pyramidal neurons reflect the expression of homomeric Kv4.2 channels. The experiments here were designed to define directly the role of Kv4.2 in the generation ofIAin cortical pyramidal neurons and to determine the functional consequences of the targeted deletion of Kv4.2 on the resting and active membrane properties of these cells. Whole‐cell voltage‐clamp recordings, obtained from visual cortical pyramidal neurons isolated from mice in which theKCND2(Kv4.2) locus was disrupted (Kv4.2‐/‐ mice), revealed thatIAis indeed eliminated. In addition, the densities of other Kv current components, specificallyIKandIss, are increased significantly (P< 0.001) in most (∼80%) Kv4.2‐/‐ cells. The deletion ofKCND2(Kv4.2) and the elimination ofIAis also accompanied by the loss of the Kv4 channel accessory protein KChIP3, suggesting that in the absence of Kv4.2, the KChIP3 protein is targeted for degradation. The expression levels of several Kv α subunits (Kv4.3, Kv1.4, Kv2.1, Kv2.2), however, are not measurably altered in Kv4.2‐/‐ cortices. AlthoughIAis eliminated in Kv4.2‐/‐ pyramidal neurons, the mean ±s.e.m.current threshold for action potential generation and the waveforms of action potentials are indistinguishable from those recorded from wild‐type cells. Repetitive firing is also maintained in Kv4.2‐/‐ cortical pyramidal neurons, suggesting that the increased densities ofIKandIsscompensate for thein vivoloss ofIA.
Postural control at the human wrist
Authors: Chew John Z. Z. , Gandevia Simon C. , Fitzpatrick Richard C.
Published: January 2008

In our movements and posture, we always act against a physical load. A key property of any load is its elastic stiffness (K), which describes how the force required to hold it must change with position. Here we examine how load stiffness affects the ability to maintain a stable posture at the wrist. Loads having positive (like a spring) and negative stiffness (like an inverted pendulum) were created by varying the position of weights on multiarm rigid pendulum. Subjects (n= 9) held 15 loads (K=± 0.04, ± 0.01 and 0 N m deg−1 at mean torques of 0.2, 0.4 and 0.6 N m) still for 60 s. Residual wrist movement (sway) increased with mean torque and increased as stiffness became more negative. Large effects of load stiffness were seen at low frequencies (< 1.5 Hz) but not at higher frequencies that reflect load resonance and reflex activity. Subjects accurately perceived their postural sway while holding the loads but measured psychophysical thresholds showed that load stiffness was not perceived. We conclude that load stiffness, independent of force levels, affects the ability to control a load and that the postural control process relies on perception and volitional tracking rather than more automatic reflex pathways. Despite an awareness of their postural errors, we see no evidence for adaptation of postural control processes to compensate for changes in load properties. This is unlike the adaptation of feedforward control processes that produce targeted volitional movements when load properties are altered. We propose that postural control and movement control are fundamentally different neural processes.
Spike Ca2+influx upmodulates the spike afterdepolarization and bursting via intracellular inhibition of KV7/M channels
Authors: Chen Shmuel , Yaari Yoel
Published: January 2008

In principal brain neurons, activation of Ca2+channels during an action potential, or spike, causes Ca2+entry into the cytosol within a millisecond. This in turn causes rapid activation of large conductance Ca2+‐gated channels, which enhances repolarization and abbreviates the spike. Here we describe another remarkable consequence of spike Ca2+entry: enhancement of the spike afterdepolarization. This action is also mediated by intracellular modulation of a particular class of K+channels, namely by inhibition of KV7 (KCNQ) channels. These channels generate the subthreshold, non‐inactivating M‐type K+current, whose activation curtails the spike afterdepolarization. Inhibition of KV7/M by spike Ca2+entry allows the spike afterdepolarization to grow and can convert solitary spikes into high‐frequency bursts of action potentials. Through this novel intracellular modulatory action, Ca2+spike entry regulates the discharge mode and the signalling capacity of principal brain neurons.
Block of inhibitory junction potentials and TREK‐1 channels in murine colon by Ca2+ store‐active drugs
Authors: Hwang Sung Jin , O'Kane Neil , Singer Cherie , Ward Sean M. , Sanders Kenton M. , Koh Sang Don
Published: January 2008

Post‐junctional enteric inhibitory responses are composed of at least two components attributed to the release of a purine and nitric oxide (NO). The nitrergic component is characterized by membrane potential hyperpolarization; however, the conductances involved and the role of Ca2+ stores in regulating these conductances are controversial. Conventional microelectrode recordings were performed in intact muscle strips and whole‐cell voltage clamp experiments were performed on freshly dispersed cells and COS7 cells stably transfected with TREK‐1 channels. Here we show that several Ca2+ store‐active compounds, including caffeine, ryanodine, and cyclopiazonic acid, reduce inhibitory junction potentials and responses to sodium nitroprusside in murine colonic muscles. We previously proposed that two‐pore K+ channels of the TREK family mediate a portion of the hyperpolarization response to NO in colonic muscles. We tested the effects of Ca2+ store‐active drugs in COS cells expressing murine TREK‐1 channels and found these compounds block TREK‐1 currents. These effects were greatly attenuated by dialysing cells with protein kinase A inhibitory peptide (PKAI). Caffeine also blocked stretch‐dependent K+ (SDK) channels, thought to be due to expression of TREK channels, in colonic myocytes, but these effects were not apparent in excised patches. Taken together our data show that Ca2+ store‐active compounds inhibit TREK‐1 channels, native SDK channels, and nitrergic inhibitory junction potentials. These effects appear to be due, in part, to the cAMP/PKA stimulatory actions of these drugs and inhibitory effects of TREK channels.
‘Pressure–flow‘‐triggered intracellular Ca2+ transients in rat cardiac myocytes: possible mechanisms and role of mitochondria
Authors: Belmonte Stephen , Morad Martin
Published: January 2008

Cardiac myocytes, in the intact heart, are exposed to shear/fluid forces during each cardiac cycle. Here we describe a novel Ca2+ signalling pathway, generated by ‘pressurized flows’ (PFs) of solutions, resulting in the activation of slowly developing (∼300 ms) Ca2+ transients lasting ∼1700 ms at room temperature. Though subsequent PFs (applied some 10–30 s later) produced much smaller or undetectable responses, such transients could be reactivated following caffeine‐ or KCl‐induced Ca2+ releases, suggesting that a small, but replenishable, Ca2+ pool serves as the source for their activation. PF‐triggered Ca2+ transients could be activated in Ca2+‐free solutions or in solutions that block voltage‐gated Ca2+ channels, stretch‐activated channels (SACs), or the Na+–Ca2+ exchanger (NCX), using Cd2+, Gd3+, or Ni2+, respectively. PF‐triggered Ca2+ transients were significantly smaller in quiescent than in electrically paced myocytes. Paced Ca2+ transients activated at the peak of PF‐triggered Ca2+ transients were not significantly smaller than those produced normally, suggesting functionally separate Ca2+ pools for paced and PF‐triggered transients. Suppression of nitric oxide (NO) or IP3 signalling pathways did not alter the PF‐triggered Ca2+ transients. On the other hand, mitochondrial metabolic uncoupler FCCP, in the presence of oligomycin (to prevent ATP depletion), reversibly suppressed PF‐triggered Ca2+ transients, as did the mitochondrial Ca2+ uniporter (mCU) blocker, Ru360. Reducing agent DTT and reactive oxygen species (ROS) scavenger tempol, as well as mitochondrial NCX (mNCX) blocker CGP‐37157, inhibited PF‐triggered Ca2+ transients. In rhod‐2 AM‐loaded and permeabilized cells, confocal imaging of mitochondrial Ca2+ showed a transient increase in Ca2+ on caffeine exposure and a decrease in mitochondrial Ca2+ on application of PF pulses of solution. These signals were strongly suppressed by either Na+‐free or CGP‐37157‐containing solutions, implicating mNCX in mediating the Ca2+ release process. We conclude that subjecting rat cardiac myocytes to pressurized flow pulses of solutions triggers the release of Ca2+ from a store that appears to access mitochondrial Ca2+.
Electronic Liquid Crystal State in the High-Temperature Superconductor YBa
2
Cu
3
O
6.45
Authors: Hinkov V. , Haug D. , Fauqué B. , Bourges P. , Sidis Y. , Ivanov A. , Bernhard C. , Lin C. T. , Keimer B.
Published: January 2008

Electronic phases with symmetry properties matching those of conventional liquid crystals have recently been discovered in transport experiments on semiconductor heterostructures and metal oxides at millikelvin temperatures. We report the spontaneous onset of a one-dimensional, incommensurate modulation of the spin system in the high-transition-temperature superconductor YBa
2
Cu
3
O
6.45
upon cooling below ∼150 kelvin, whereas static magnetic order is absent above 2 kelvin. The evolution of this modulation with temperature and doping parallels that of the in-plane anisotropy of the resistivity, indicating an electronic nematic phase that is stable over a wide temperature range. The results suggest that soft spin fluctuations are a microscopic route toward electronic liquid crystals and that nematic order can coexist with high-temperature superconductivity in underdoped cuprates.
Ontogeny of body size and shape of Antarctic and subantarctic fur seals
Authors: Luque Sebastián P. , Miller Edward H. , Arnould John P.Y. , Chambellant Magaly , Guinet Christophe
Published: January 2008

Pre- and post-weaning functional demands on body size and shape of mammals are often in conflict, especially in species where weaning involves a change of habitat. Compared with long lactations, brief lactations are expected to be associated with fast rates of development and attainment of adult traits. We describe allometry and growth for several morphological traits in two closely related fur seal species with large differences in lactation duration at a sympatric site. Longitudinal data were collected from Antarctic ( Arctocephalus gazella (Peters, 1875); 120 d lactation) and subantarctic ( Arctocephalus tropicalis (Gray, 1872); 300 d lactation) fur seals. Body mass was similar in neonates of both species, but A. gazella neonates were longer, less voluminous, and had larger foreflippers. The species were similar in rate of preweaning growth in body mass, but growth rates of linear variables were faster for A. gazella pups. Consequently, neonatal differences in body shape increased over lactation, and A. gazella pups approached adult body shape faster than did A. tropicalis pups. Our results indicate that preweaning growth is associated with significant changes in body shape, involving the acquisition of a longer, more slender body with larger foreflippers in A. gazella. These differences suggest that A. gazella pups are physically more mature at approximately 100 d of age (close to weaning age) than A. tropicalis pups of the same age.
Real-world challenges to, and capabilities of, the gekkotan adhesive system: contrasting the rough and the smooth
Authors: Russell A.P. , Johnson M.K.
Published: January 2008

Many species of gekkotan lizards possess adhesive subdigital pads that allow them to adhere to, and move easily on, a wide variety of surfaces. However, although the mechanism of adhesion and the potential adhesive capacity of this system have been extensively studied, the adaptive value of these structures and their deployment in natural situations have rarely been examined. The maximal adhesive capacity of gekkotan setal fields has been shown to greatly exceed the force needed to support the body. This high adhesive potential is likely an adaptation for movement on the natural surfaces that these lizards encounter in their environment. Natural surfaces may be rough, undulant, and unpredictable, and provide only limited, patchy areas with which adhesive structures can make contact. Here we examine the microtopography of rock surfaces used by a southern African species of gecko of the genus Rhoptropus Peters, 1869, and compare this to the form, configuration, compliance, and functional morphology of the setal fields of this species. Our results demonstrate that the structure and topology of natural surfaces are important factors in understanding the design of subdigital pads, and provide insight into the evolution of the adhesive system of gekkonid lizards and its adaptive value on topographically unpredictable surfaces.