bluuebunny/crossref_metadata_2025 huggingface dataset:
Study of Flow and Heat Transfer Characteristics in Asymmetrically Heated Sintered Porous Heat Sinks With Periodical Baffles
Authors: Jeng Tzer-Ming , Tzeng Sheng-Chung
Published: September 2006

This work numerically examined the mechanism of heat transfer in a sintered porous heat sink with baffles. A channel filled with the sintered porous heat sink was asymmetrically heated and metallic baffles were periodically mounted on the heated surface. The fluid medium was air. The results indicate that no recirculation occurred between baffles. The metallic baffle obtained heat from the heated surface by conduction directly from the heated surface and indirectly through the porous media. It dissipated heat to the fluid that passed over the zone above the baffle. The Nusselt numbers in the cases with baffles exceeded those in cases without a baffle. The enhancement in the average Nusselt numbers of sintered porous heat sinks with baffles increased as the Reynolds number (Re) declined; the baffle height (h∕H) increased; the baffle length (w∕H) increased, or the baffle pitch (XL) decreased. However, at Re=500, the average Nusselt number in the case with h∕H=0.3 was higher than those with h∕H=0.7, 0.5, and 0.1. Additionally, the minimum enhancement appeared at around Re=3000 for various h∕H, w∕H, and XL. For the cases with h∕H⩽0.3 and various w∕H as well as XL, at Re>3000, sintered porous heat sinks with baffles insignificantly improved heat transfer.
Metal Foam and Finned Metal Foam Heat Sinks for Electronics Cooling in Buoyancy-Induced Convection
Authors: Bhattacharya A. , Mahajan R. L.
Published: September 2006

In this paper, we present our recent experimental results on buoyancy-induced convection in aluminum metal foams of different pore densities [corresponding to 5, 10, 20, and 40 pores per in. (PPI)] and porosities (0.89–0.96). The results show that compared to a heated surface, the heat transfer coefficients in these heat sinks are five to six times higher. However, when compared to commercially available heat sinks of similar dimensions, the enhancement is found to be marginal. The experimental results also show that for a given pore size, the heat transfer rate increases with porosity, suggesting the dominant role played by conduction in enhancing heat transfer. On the other hand, if the porosity is held constant, the heat transfer rate is found to be lower at higher pore densities. This can be attributed to the higher permeability with the larger pores, which allows higher entrainment of air through the porous medium. New empirical correlations are proposed for the estimation of Nusselt number in terms of Rayleigh and Darcy numbers. We also report our results on novel finned metal foam heat sinks in natural convection. Experiments were conducted on aluminum foams of 90% porosity with 5 and 20 PPI with one, two, and four aluminum fins inserted in the foam. All of these heat sinks were fabricated in-house. The results show that the finned metal foam heat sinks are superior in thermal performance compared to the normal metal foam and conventional finned heat sinks. The heat transfer increases with an increase in the number of fins. However, the relative enhancement is found to decrease with each additional fin. The indication is that there exists an optimum number of fins beyond which the enhancement in heat transfer, due to increased surface area, is offset by the retarding effect of overlapping thermal boundary layers. Similar to normal metal foams, the 5 PPI samples are found to give higher values of h compared to the 20 PPI samples due to higher permeability of the porous medium. Future work is planned to arrive at the optimal heat sink configuration for even larger enhancement in heat transfer.
Transient Thermal Analysis for Board-Level Chip-Scale Packages Subjected to Coupled Power and Thermal Cycling Test Conditions
Authors: Wang Tong Hong , Lee Chang-Chi , Lai Yi-Shao , Lin Yu-Cheng
Published: September 2006

In this work, thermal characteristics of a board-level chip-scale package, subjected to coupled power and thermal cycling test conditions defined by JEDEC, are investigated through the transient thermal analysis. Tabular boundary conditions are utilized to deal with time-varying thermal boundary conditions brought by thermal cycling. It is obvious from the analysis that the presence of power cycling leads to a significant deviation of the junction temperature from the thermal cycling profile. However, for components away from the die, the deviation is insignificant. Moreover, for low-power applications, temperature histories from coupled power and thermal cycling are approximately linear combinations of temperature histories from pure power cycling and the ones from pure thermal cycling.
Heat Sinks With Enhanced Heat Transfer Capability for Electronic Cooling Applications
Authors: Small Evan , Sadeghipour Sadegh M. , Asheghi Mehdi
Published: September 2006

In a competition at Carnegie Mellon University, the mechanical engineering students designed and manufactured 27 heat sinks. The heat sinks were then tested for thermal performance in cooling a mock processor. A heat sink with three rows of 9, 8, and 9 dimpled rectangular fins in staggered configuration performed the best, while having the least total volume (about 25% less than the set value). Validation of the observed thermal performance of this heat sink by experimentation and numerical simulations has motivated the present investigation. Thermal performance of the heat sinks with and without dimples have been evaluated and compared. Results of both the measurements and simulations indicate that dimples do in fact improve heat transfer capability of the heat sinks. However, dimples cause more pressure drop in the air flow. Keeping the total volume of the heat sink and the height of the fins constant and changing the number of the fins and their arrangement show that there is an optimum number of fins for the best performance of the heat sink. The optimum fin numbers are different for inline and staggered arrangements.
A Three-Dimensional Solder Shape Model Incorporating Top Pad Inclination and Misalignment
Authors: Rayasam Mahidhar , Subbarayan Ganesh
Published: September 2006

In this technical brief, we describe a simple, yet versatile solder shape prediction model that can handle inclination (as is likely to occur when warped substrates are used) and misalignment of the top pad of the solder joint relative to the bottom pad. The developed model is general in nature and is demonstrated on a solder joint with circular top and bottom pads and on a stud joint where the interconnection is to a stud on which the wetted area is to be determined through simulation. The model was able to accurately predict the solder profiles from literature with an error of ±5%. A program written within the MATHEMATICA® environment was developed and used for the above simulations.
Reliability of Lead-Free Solder Joints
Authors: Lau John H.
Published: September 2006

Reliability of the restriction of the use of certain hazardous substances in electrical and electronic equipment compliant products is investigated in this study. Emphasis is placed on the lead-free solder joint reliability. Solder is the electrical and mechanical “glue” of electronics assemblies. Will lead-free solders provide the characteristics necessary to allow the world to depend on it in the future? This paper cannot answer this question; however, it will help all participants in the soldering world better understand what needs to be done in order to answer this question and plan for the future.
Matter from outside our solar system—new insights, Part I: The astrophysical framework
Authors: Wefel John P.
Published: September 2006

Cosmic rays are an interesting sample of galactic matter. The element abundances contain information on the source matter, the acceleration process, and the history of particle propagation in the galaxy. Unfortunately, this information cannot be unlocked completely due to the unknown nature of the acceleration process. However, the cosmic-ray isotopes provide the key for studying the matter at the cosmic-ray source. Is the nucleosynthetic history of this matter the same as matter in our solar system? This long-standing question is beginning to be answered due, at least partly, to the new research results in cosmic-ray physics. The theory of nucleosynthesis for heavy elements during stellar evolution has been reviewed to provide a basis for the interpretation of the differences or similarities between the isotopic composition of cosmic-ray source matter and material from the solar system. Particular attention was devoted to the elements neon, magnesium, and silicon since these are the elements whose isotopes have been studied recently in the cosmic rays and provide the best current information on the composition of the cosmic-ray source matter. (AIP)
NEWSLETTER: Council on Physics in Education
Authors: Moravcsik Michael J.
Published: September 2006

Continuing its use of the Newsletter to bring you reports of the activities of the AAPT Committees, the Council on Physics in Education brings you, in this issue, the second report from the Committee on International Education in Physics.
Weight and Weightlessness
Authors: Sears Francis W.
Published: September 2006

A definition of "weight" becomes more important now that manmade satellites, some with astronauts, revolve about the earth. Does the astronaut become weightless? Definitions and discussion of the terms weight and apparent weight are given. One definition is proposed as the best to use in a physics course.
What Does Acoustics Have To Offer?
Authors: Lindsay R. B.
Published: September 2006

A general survey of acoustics as one of the old yet very modern fields of physics is given. Its role in affording us one of the means we learn of the world about us is described. Not only does sound furnish a means of communication, but through experiments involving sound waves, we can discover some properties of matter that at first seem very unrelated to sound. Applications in industry, in physiology, in psychology and other fields are cited. The students majoring in physics can find ample challenge in working in acoustics.

In the writing of this article, the support in part of the Office of Naval Research is gratefully acknowledged.
The Relation of Physics to Other Sciences
Authors: Feynman Richard P.
Published: September 2006

Through the courtesy of the Addison-Wesley Publishing Company of Reading, Massachusetts we are able to publish one of the opening chapters of the Feynman Lectures in Physics. This is a new book based on the lectures given by Dr. Feynman in the introductory course at the California Institute of Technology. A second chapter of this refreshingly different but delightfully rigorous introduction to college physics will be published later.
APPARATUS FOR TEACHING PHYSICS: The Eduquip Air Track, An Apparatus Evaluation
Authors: Manfre Edward T. , Neff Robert F.
Published: September 2006

This is the fourth in a series of apparatus evaluation studies which are being performed by active physics teachers with the cooperation of the AAPT Apparatus Committee as a service to the profession. The Eduquip Air Track was selected for study because of its unique design which incorporates a track and an air blower in one integral piece.
Stars and Nuclei. Part II
Authors: Ames Oakes
Published: September 2006

A brief review of how we know that nuclear reactions are the main source of stellar energy, how they synthesize the elements, and how they determine the course of stellar evolution.
Therapy-Induced Acute Recruitment of Circulating Endothelial Progenitor Cells to Tumors
Authors: Shaked Yuval , Ciarrocchi Alessia , Franco Marcela , Lee Christina R. , Man Shan , Cheung Alison M. , Hicklin Daniel J. , Chaplin David , Foster F. Stuart , Benezra Robert , Kerbel Robert S.
Published: September 2006

The contribution of bone marrow–derived circulating endothelial progenitor cells (CEPs) to tumor angiogenesis has been controversial, primarily because of their low numbers in blood vessels of untreated tumors. We show that treatment of tumor-bearing mice with vascular disrupting agents (VDAs) leads to an acute mobilization of CEPs, which home to the viable tumor rim that characteristically remains after such therapy. Disruption of this CEP spike by antiangiogenic drugs or by genetic manipulation resulted in marked reductions in tumor rim size and blood flow as well as enhanced VDA antitumor activity. These findings also provide a mechanistic rationale for the enhanced efficacy of VDAs when combined with antiangiogenic drugs.
Self-Healing Pulse-Like Shear Ruptures in the Laboratory
Authors: Lykotrafitis George , Rosakis Ares J. , Ravichandran Guruswami
Published: September 2006

Models predict that dynamic shear ruptures during earthquake faulting occur as either sliding cracks, where a large section of the interface slides behind a fast-moving rupture front, or self-healing slip pulses, where the fault relocks shortly behind the rupture front. We report experimental visualizations of crack-like, pulse-like, and mixed rupture modes propagating along frictionally held, “incoherent” interfaces separating identical solids, and we describe the conditions under which those modes develop. A combination of simultaneously performed measurements via dynamic photoelasticity and laser interferometry reveals the rupture mode type, the exact point of rupture initiation, the sliding velocity history, and the rupture propagation speed.
Response to Comments on "A Keystone Mutualism Drives Pattern in a Power Function"
Authors: Vandermeer John , Perfecto Ivette
Published: September 2006

The comments by Alonso and Pascual and by Pueyo and Jovani clarify the power law distribution of subpopulations of the scale insect
Coccus viridis
. The low density deviations are now seen as part of a negative binomial distribution and the high density deviations as resulting from a change in the parameters of the power law. Our biological conclusion that an ant mutualism modifies the form of the power law is thus strengthened.
A Genomewide Search for Ribozymes Reveals an HDV-Like Sequence in the Human
CPEB3
Gene
Authors: Salehi-Ashtiani Kourosh , Lupták Andrej , Litovchick Alexander , Szostak Jack W.
Published: September 2006

Ribozymes are thought to have played a pivotal role in the early evolution of life, but relatively few have been identified in modern organisms. We performed an in vitro selection aimed at isolating self-cleaving RNAs from the human genome. The selection yielded several ribozymes, one of which is a conserved mammalian sequence that resides in an intron of the
CPEB3
gene, which belongs to a family of genes regulating messenger RNA polyadenylation. The CPEB3 ribozyme is structurally and biochemically related to the human hepatitis delta virus (HDV) ribozymes. The occurrence of this ribozyme exclusively in mammals suggests that it may have evolved as recently as 200 million years ago. We postulate that HDV arose from the human transcriptome.
Observations of Biologically Generated Turbulence in a Coastal Inlet
Authors: Kunze Eric , Dower John F. , Beveridge Ian , Dewey Richard , Bartlett Kevin P.
Published: September 2006

Measurements in a coastal inlet revealed turbulence that was three to four orders of magnitude larger during the dusk ascent of a dense acoustic-scattering layer of krill than during the day, elevating daily-averaged mixing in the inlet by a factor of 100. Because vertically migrating layers of swimming organisms are found in much of the ocean, biologically generated turbulence may affect (i) the transport of inorganic nutrients to the often nutrient-depleted surface layer from underlying nutrient-rich stratified waters to affect biological productivity and (ii) the exchange of atmospheric gases such as CO
2
with the stratified ocean interior, which has no direct communication with the atmosphere.
A CONSISTENT QUASIPARTICLE PICTURE OF QUARK–GLUON PLASMA AND THE VELOCITY OF SOUND
Authors: GHOSH SANJAY K. , MUKHERJEE TAMAL K. , RAHA SIBAJI
Published: September 2006

A thermodynamically consistent density dependent quark mass model has been used to study the velocity of sound in a hot quark–gluon plasma. The results are compared with the recent lattice data.
SKYRMION AND SKYRME-BLACK HOLES IN de SITTER SPACETIME
Authors: BRIHAYE YVES , DELSATE TERENCE
Published: September 2006

Numerical arguments are presented for the existence of regular and black hole solutions of the Einstein–Skyrme equations with a positive cosmological constant. These classical configurations approach asymptotically the de Sitter spacetime. The main properties of the solutions and the differences with respect to the asymptotically flat ones are discussed. In particular our results suggest that, for a positive cosmological constant, the mass evaluated as timelike infinity in infinite. Special emphasis is set to de Sitter black holes Skyrmions which display two horizons.
MATHEMATICAL MODELING OF LIVING CELL METABOLISM USING THE METHOD OF STEADY-STATE STOICHIOMETRIC FLUX BALANCE
Authors: DROZDOV-TIKHOMIROV L. N. , SCURIDA G. I. , DAVIDOV A. V. , ALEXANDROV A. A. , ZVYAGILSKAYA R. A.
Published: September 2006

This approach uses a set of algebraic linear equations for reaction rates (the method of steady-state stoichiometric flux balance) to model the purposeful metabolism of the living self-reproducing biochemical system (i.e. cell), which persists in steady-state growth. Linear programming (SIMPLEX method) is used to derive the solution for the model equations set (determining reaction rates which provide flux balance at given conditions). Here, we demonstrate the approach through the mathematical modeling of steady-state metabolism in Saccharomyces cerevisiae mitochondria.
The Obesity Epidemic: Current and Future Pharmacological Treatments
Authors: Hofbauer Karl G. , Nicholson Janet R. , Boss Olivier
Published: September 2006

The unabated rise in the prevalence of obesity is a challenge for global health care systems. Efforts to reverse this trend by dietary or behavioral counseling have not been successful, which has stimulated efforts to find a role for pharmacotherapy. Currently only a small number of antiobesity drugs are approved for long-term use and only a few compounds are in clinical development. Despite recent progress in the understanding of the regulation of energy balance, drug discovery has been less productive than expected. In the present review, the clinically available antiobesity agents are discussed. Examples of drug candidates that are currently in development are given and the possible future range of antiobesity agents is illustrated by the targets being addressed in drug discovery. Finally, the efficacy of antiobesity agents and their value in the treatment of obesity are assessed in comparison with other therapeutic approaches, such as surgery and changes in lifestyle.
Defective coupling of apical PTH receptors to phospholipase C prevents internalization of the Na+-phosphate cotransporter NaPi-IIa in Nherf1-deficient mice
Authors: Capuano Paola , Bacic Desa , Roos Marcel , Gisler Serge M. , Stange Gerti , Biber Jürg , Kaissling Brigitte , Weinman Edward J. , Shenolikar Shirish , Wagner Carsten A. , Murer Heini
Published: September 2006

Phosphate reabsorption in the renal proximal tubule occurs mostly via the type IIa Na+-phosphate cotransporter (NaPi-IIa) in the brush border membrane (BBM). The activity and localization of NaPi-IIa are regulated, among other factors, by parathyroid hormone (PTH). NaPi-IIa interacts in vitro via its last three COOH-terminal amino acids with the PDZ protein Na+/H+-exchanger isoform 3 regulatory factor (NHERF)-1 (NHERF1). Renal phosphate reabsorption in Nherf1-deficient mice is altered, and NaPi-IIa expression in the BBM is reduced. In addition, it has been proposed that NHERF1 and NHERF2 are important for the coupling of PTH receptors (PTHRs) to phospholipase C (PLC) and the activation of the protein kinase C pathway. We tested the role of NHERF1 in the regulation of NaPi-IIa by PTH in Nherf1-deficient mice. Immunohistochemistry and Western blotting demonstrated that stimulation of apical and basolateral receptors with PTH-(1–34) led to internalization of NaPi-IIa in wild-type and Nherf1-deficient mice. Stimulation of only apical receptors with PTH-(3–34) failed to induce internalization in Nherf1-deficient mice. Expression and localization of apical PTHRs were similar in wild-type and Nherf1-deficient mice. Activation of the protein kinase C- and A-dependent pathways with 1,2-dioctanoyl- sn-glycerol or 8-bromo-cAMP induced normal internalization of NaPi-IIa in wild-type, as well as Nherf1-deficient, mice. Stimulation of PLC activity due to apical PTHRs was impaired in Nherf1-deficient mice. These data suggest that NHERF1 in the proximal tubule is important for PTH-induced internalization of NaPi-IIa and, specifically, couples the apical PTHR to PLC.
Epigenetic regulation of integrin-linked kinase expression depending on adhesion of gastric carcinoma cells
Authors: Kim Yong-Bae , Lee Sung-Yul , Ye Sang-Kyu , Lee Jung Weon
Published: September 2006

Cell adhesion to the extracellular matrix (ECM) regulates gene expressions in diverse dynamic environments. However, the manner in which gene expressions are regulated by extracellular cues is largely unknown. In this study, suspended gastric carcinoma cells showed higher basal and transforming growth factor-β1 (TGFβ1)-mediated acetylations of histone 3 (H3) and Lys9 of H3 and levels of integrin-linked kinase (ILK) mRNA and protein than did fibronectin-adherent cells did. Moreover, the insignificant acetylation and ILK expression in adherent cells were recovered by alterations of integrin signaling and actin organization, indicating a connection between cytoplasmic and nuclear changes. Higher acetylations in suspended cells were correlated with associations between Smad4, p300/CBP, and Lys9-acetylated H3. Meanwhile, adherent cells showed more associations between HDAC3, Ski, and MeCP2. Chromatin immunoprecipitations with anti-acetylated H3, Lys9-acetylated H3, or p300/CBP antibody resulted in more coprecipitated ILK promoter, correlated with enhanced ILK mRNA and protein levels, in suspended cells. Moreover, ILK expression inversely regulated cell adhesion to ECM proteins, and its overexpression enhanced cell growth in soft agar. These observations indicate that cell adhesion and/or its related molecular basis regulate epigenetic mechanisms leading to a loss of ILK transcription, which in turn regulates cell adhesion property in a feedback linkage.
Proximal tubular epithelial cells are generated by division of differentiated cells in the healthy kidney
Authors: Vogetseder Alexander , Palan Thomas , Bacic Desa , Kaissling Brigitte , Le Hir Michel
Published: September 2006

We searched for evidence for a contribution of stem cells in growth of the proximal S3 segments of healthy rats. According to the stem cell model, stem cells are undifferentiated and slow cycling; the bulk of cycling cells are transit amplifying, rapidly cycling cells. We show the following. 1) By continuous application of a thymidine analog (ThA) for 7 days, S3 proximal epithelial cells in healthy kidneys display a high-cycling rate. 2) Slow-cycling cells, identified by lack of ThA uptake during 14 days of continuous ThA application up to death and by expression of the cell cycle protein Ki67 at death, have the same degree of differentiation as quiescent cells. 3) To detect rapidly cycling cells, rats were killed at various time points after injection of a ThA. Double immunofluorescence for ThA and a cell cycle marker was performed, with colocalization indicating successive divisions. During one week after division, daughter cells display a very low proliferation rate, indicating the absence of rapidly cycling cells. 4) Labeling with cyclin D1 showed that this low proliferation rate is due to cycle arrest. 5) More than 50% of the S3 cells entered the cell cycle 36 h after a potent proliferative stimulus (lead acetate injection). We conclude that generation of new cells in the proximal tubule relies on division of differentiated, normally slow-cycling cells. These may rapidly enter the cycle under an adequate stimulus.
siRNA knock down of casein kinase 2 increases force and cross-bridge cycling rates in vascular smooth muscle
Authors: Smolock Elaine M. , Wang Tanchun , Nolt Jocelyn K. , Moreland Robert S.
Published: September 2006

Contraction of smooth muscle involves myosin light chain (MLC) kinase catalyzed phosphorylation of the regulatory MLC, activation of myosin, and the development of force. However, this cannot account for all aspects of a smooth muscle contraction, suggesting that other regulatory mechanisms exist. One potentially important technique to study alternative sites of contractile regulation is the use of small interfering RNA (siRNA). The goal of this study was to determine whether siRNA technology can decrease the levels of a specific protein and allow for the determination of how that protein affects contractile regulation. To achieve this goal, we tested the hypothesis that casein kinase 2 (CK2) is part of the complex regulatory scheme present in vascular smooth muscle. Using intact strips of swine carotid artery, we determined that siRNA against CK2 produced a tissue that resulted in a ∼60% knockdown after 4 days in organ culture. Intact strips of vascular tissue depleted of CK2 produced greater levels of force and exhibited an increased sensitivity to all stimuli tested. This was accompanied by an increase in cross-bridge cycling rates but not by a change in MLC phosphorylation levels. α-Toxin-permeabilized vascular tissue depleted of CK2 also showed an increased sensitivity to calcium compared with control tissues. Our results demonstrate that siRNA is a viable technique with which to study regulatory pathways in intact smooth muscle tissue. Our results also demonstrate that CK2 plays an important role in the mechanism(s) responsible for the development of force and cross-bridge cycling by a MLC phosphorylation-independent pathway.
Two populations of Thy1-positive mesenchymal cells regulate in vitro maturation of hepatic progenitor cells
Authors: Kamo Naoko , Yasuchika Kentaro , Fujii Hideaki , Hoppo Toshitaka , Machimoto Takafumi , Ishii Takamichi , Fujita Naoya , Tsuruo Takashi , Yamashita Jun K. , Kubo Hajime , Ikai Iwao
Published: September 2006

We previously reported that the in vitro maturation of CD49f+Thy1−CD45− (CD49f positive) fetal hepatic progenitor cells (HPCs) is supported by Thy1-positive mesenchymal cells derived from the fetal liver. These mesenchymal cell preparations contain two populations, one of a cuboidal shape and the other spindle shaped in morphology. In this study, we determined that the mucin-type transmembrane glycoprotein gp38 could distinguish cuboidal cells from spindle cells by immunocytochemistry. RT-PCR analysis revealed differences between isolated CD49f±Thy1+gp38+CD45− (gp38 positive) cells and CD49f±Thy1+gp38−CD45− (gp38 negative) cells, whereas both cells expressed mesenchymal cell markers. The coculture with gp38-positive cells promoted the maturation of CD49f-positive HPCs, which was estimated by positivity for periodic acid-Schiff (PAS) staining, whereas the coculture with gp38-negative cells maintained CD49f-positive HPCs negative for PAS staining. The expression of mature hepatocyte markers, such as tyrosine aminotransferase, tryptophan-2,3-dioxygenase, and glucose-6-phosphatase, were upregulated on HPCs by coculture with gp38-positive cells. Furthermore, transmission electron microscopy revealed the acquisition of mature hepatocyte features by HPCs cocultured with gp38-positive cells. This effect on maturation of HPCs was inhibited by the addition of conditioned medium derived from gp38-negative cells. By contrast, the upregulation of bromodeoxyuridine incorporation by HPCs demonstrated the proliferative effect of coculture with gp38-negative cells. In conclusion, these results suggest that in vitro maturation of HPCs promoted by gp38-positive cells may be opposed by an inhibitory effect of gp38-negative cells, which likely maintain the immature, proliferative state of HPCs.
Vascular dysfunction in S1P2 sphingosine 1-phosphate receptor knockout mice
Authors: Lorenz John N. , Arend Lois J. , Robitz Rachel , Paul Richard J. , MacLennan A. John
Published: September 2006

There is growing evidence that sphingosine 1-phosphate (S1P) plays an important role in regulating the development, morphology, and function of the cardiovascular system. There is little data, however, regarding the relative contribution of endogenous S1P and its cognate receptors (referred to as S1P1–5) to cardiovascular homeostasis. We used S1P2 receptor knockout mice (S1P2−/−) to evaluate the role of S1P2 in heart and vascular function. There were no significant differences in blood pressure between wild-type and S1P2−/− mice, measured in awake mice. Cardiac function, evaluated in situ by using a Millar catheter, was also not different in S1P2−/− mice under baseline or stimulated conditions. In vivo analysis of vascular function by flowmetry revealed decreases in mesenteric and renal resistance in S1P2−/− mice, especially during vasoconstriction with phenylephrine. In intact aortic rings, the concentration-force relations for both KCl and phenylephrine were right shifted in S1P2−/− mice, whereas the maximal isometric forces were not different. By contrast, in deendothelialized rings the concentration-force relations were not different but the maximal force was significantly greater in S1P2−/− aorta. Histologically, there were no apparent differences in vascular morphology. These data suggest that the S1P2 receptor plays an important role in the function of the vasculature and is an important mediator of normal hemodynamics. This is mediated, at least in part, through an effect on the endothelium, but direct effects on vascular smooth muscle cannot be ruled out and require further investigation.
Effect of sex hormones on renal estrogen and angiotensin type 1 receptors in female and male rats
Authors: Rogers Jennifer L. , Mitchell Adam R. , Maric Christine , Sandberg Kathryn , Myers Adam , Mulroney Susan E.
Published: September 2006

Although the mechanisms are not understood, evidence suggests that 17β-estradiol (E2) confers protection from cardiovascular and renal complications in many diseases. We have reported that E2 decreases angiotensin type 1 receptors (AT1Rs) in different tissues and hypothesize that E2 exerts tonic inhibition on AT1Rs, reducing effects of ANG II. This study determined the effects of E2 and dihydrotestosterone (DHT) on cortical estrogen receptors (ERs) and glomerular AT1R binding in rats. Animals underwent sham operation, ovariectomy (Ovx) or orchidectomy (Cas) and were treated (Ovx ± E2; Cas ± DHT) for 3 wk. Cortical ERα protein was 2.5 times greater, and ERβ was 80% less in females vs. males ( P < 0.01). Glomerular AT1R binding was lower in females than males [4,657 ± 838 vs. 7,457 ± 467 counts per minute (cpm), P < 0.01]. Ovx reduced ERα protein by 50%, whereas E2 increased ERα expression after Ovx. The decrease in cortical ERα in Ovx rats was associated with a significant increase in AT1R binding (6,908 ± 609 cpm), and E2 prevented this increase. There was no change in ERα or AT1R binding following Cas ± DHT (25 mg) treatment, although Cas did elevate cortical ERβ (P < 0.01). Interestingly, the high dose DHT (200 mg) elevated ERα 150% above intact levels and profoundly decreased AT1R binding (1,824 ± 705 cpm, P < 0.001 vs. intact male). This indicates that under normal conditions, glomerular AT1R binding is significantly greater in male than female animals, which may be important in development of cardiovascular and renal disease in males. Furthermore, E2 regulates ERα and is inversely associated with glomerular AT1R binding, supporting our hypothesis that E2 tonically suppresses AT1Rs and suggesting a potential mechanism for the protective effects of estrogen.
Pre-existing inflammatory state compromises heat tolerance in rats exposed to heat stress
Authors: Lim Chin Leong , Wilson Gary , Brown Lindsay , Coombes Jeff S. , Mackinnon Laurel T.
Published: September 2006

This study investigated the roles of endotoxemia and heat-induced tissue damage in the pathology of heat stroke. In groups of eight, male Wistar rats were treated with heat exposure only (HE), or heat exposure with turpentine (T+HE), dexamethasone (D+HE), and turpentine and dexamethasone combined (TD+HE). The rats remained sedated for 2 h after receiving the respective treatments, followed by heat exposure until the core temperature (Tc) was 42°C for 15 min; control rats received turpentine (T), dexamethasone (D), and turpentine and dexamethasone (TD) without heat stress. Blood samples were collected before treatment ( baseline I), after 2 h of passive rest ( baseline II), at Tc 40°C (T40), and 15 min after achieving Tc 42°C (T42). No rats died in the nonheat-stressed groups. Survival rate was lowest in the TD+HE rats (37.5%), followed by the HE (62.5%), T+HE (75%), and D+HE (100%) rats ( P < 0.05). The duration of survival at T42°C was shortest in the TD+HE rats (9.9 ± 6.2 min) ( P < 0.01), followed by the T+HE (11.3 ± 6.1 min) and the HE (12.2 ± 4 min) ( P < 0.05) rats. The increase in plasma IL-6 concentrations was highest in the T+HE (352%) and HE (178%) rats ( P < 0.05). D+HE treatment suppressed the increases in plasma aspartate transaminase, alanine aminotransferase, and IL-6 and LPS concentrations during severe heat stress. Heat stroke can be triggered by endotoxemia or heat-induced tissue damage, and preexisting inflammation compromises heat tolerance, whereas blocking endotoxemia increases heat tolerance.
Cortactin: The Gray Eminence of the Cytoskeleton
Authors: Cosen-Binker Laura I. , Kapus András
Published: September 2006

Cortactin, an actin filament-binding protein and target of multiple kinases, has emerged as a central element connecting signaling pathways with cytoskeleton restructuring. It is involved in a perplexingly diverse array of cellular processes, including cell motility, invasiveness, synaptogenesis, endocytosis, intercellular contact assembly, and host-pathogen interactions, where the common denominator appears to be a role in the coordination of membrane dynamics with cytoskeletal remodeling. Although in recent years our knowledge about cortactin has increased exponentially, the exact mechanisms underlying its fundamental roles remain to be defined.
Remodeling the Plasticity Debate: The Presynaptic Locus Revisited
Authors: Krueger Stefan , Fitzsimonds Reiko Maki
Published: September 2006

The cellular mechanisms contributing to long-term potentiation and activity-induced formation of glutamatergic synapses have been intensely debated. Recent studies have sparked renewed interest in the role of presynaptic components in these processes. Based on the present evidence, it appears likely that long-term plasticity utilizes both pre- and postsynaptic expression mechanisms.
Randomized Trial of Atorvastatin for Reduction of Postoperative Atrial Fibrillation in Patients Undergoing Cardiac Surgery
Authors: Patti Giuseppe , Chello Massimo , Candura Dario , Pasceri Vincenzo , D’Ambrosio Andrea , Covino Elvio , Di Sciascio Germano
Published: September 2006

Background—

Atrial fibrillation (AF) after cardiac surgery is associated with increased risk of complications, length of stay, and cost of care. Observational evidence suggests that patients who have undergone previous statin therapy have a lower incidence of postoperative AF. We tested this observation in a randomized, controlled trial.

Methods and Results—

Two hundred patients undergoing elective cardiac surgery with cardiopulmonary bypass, without previous statin treatment or history of AF, were enrolled. Patients were randomized to atorvastatin (40 mg/d, n=101) or placebo (n=99) starting 7 days before operation. The primary end point was incidence of postoperative AF; secondary end points were length of stay, 30-day major adverse cardiac and cerebrovascular events, and postoperative C-reactive protein (CRP) variations. Atorvastatin significantly reduced the incidence of AF versus placebo (35% versus 57%,
P
=0.003). Accordingly, length of stay was longer in the placebo versus atorvastatin arm (6.9±1.4 versus 6.3±1.2 days,
P
=0.001). Peak CRP levels were lower in patients without AF (
P
=0.01), irrespective of randomization assignment. Multivariable analysis showed that atorvastatin treatment conferred a 61% reduction in risk of AF (odds ratio 0.39, 95% confidence interval 0.18 to 0.85,
P
=0.017), whereas high postoperative CRP levels were associated with increased risk (odds ratio 2.0, 95% confidence interval 1.2 to 7.0,
P
=0.01). The incidence of major adverse cardiac and cerebrovascular events at 30 days was similar in the 2 arms.

Conclusions—

Treatment with atorvastatin 40 mg/d, initiated 7 days before surgery, significantly reduces the incidence of postoperative AF after elective cardiac surgery with cardiopulmonary bypass and shortens hospital stay. These results may influence practice patterns with regard to adjuvant pharmacological therapy before cardiac surgery.
Cue- versus Probe-dependent Prefrontal Cortex Activity during Contextual Remembering
Authors: Dobbins Ian G. , Han Sanghoon
Published: September 2006

Functional neuroimaging comparisons of context and item memory frequently implicate the left prefrontal cortex (PFC) during the recovery of contextually specific memories. However, because cues and probes are often presented simultaneously, this activity could reflect operations involved in planning retrieval or instead reflect later operations dependent upon the memory probes themselves, such as evaluation of probe-evoked recollections. More importantly, planning-related activity, wherein subjects reinstate details outlining the nature of desired remembrances, should occur in response to contextual memory cues even before retrieval probes are available. Using event-related functional magnetic resonance imaging, we tested this by dissociating cue- from probe-related activity during context memory for pictures. Cues forewarning contextual memory demands yielded more activity than those forewarning item memory in the left lateral precentral gyrus, midline superior frontal gyrus, and right frontopolar cortex. Thus, these anticipatory, cue-based activations indicated whether upcoming probe decisions would require contextually specific memories or not. In contrast, the left dorsolateral/midventrolateral and anterior ventrolateral PFC areas did not show differential activity until the probes were actually presented, demonstrating greater activity for context than for item memory probes. Direct comparison of proximal left PFC regions demonstrated qualitatively different response profiles across cue versus probe periods for lateral precentral versus dorsolateral regions. These results potentially isolate contextual memory-planning-related processes from subsequent processes such as the evaluation of recollections, which are necessarily dependent on individual probe features. They also demonstrate that contextual remembering recruits multiple, functionally distinct PFC processes.
Inducing Letter-by-letter Dyslexia in Normal Readers
Authors: Fiset Daniel , Gosselin Frédéric , Blais Caroline , Arguin Martin
Published: September 2006

Letter-by-letter (LBL) dyslexia is an acquired reading disorder characterized by very slow reading and a large linear word length effect. This suggests the use of a sequential LBL strategy, in sharp contrast with the parallel letter processing used by normal subjects. Recently, we have proposed that the reading difficulty of LBL dyslexics is due to a deficit in discriminating visually similar letters based on parallel letter processing [Arguin, M., Fiset, S., & Bub, D. Sequential and parallel letter processing in letter-by-letter dyslexia. Cognitive Neuropsychology, 19, 535–555, 2002]. The visual mechanisms underlying this deficit and the LBL strategy, however, are still unknown. In this article, we propose that LBL dyslexic patients have lost the ability to use, for parallel letter processing, the optimal spatial frequency band for letter and word recognition. We claim that, instead, they rely on lower spatial frequencies for parallel processing, that these lower spatial frequencies produce confusions between visually similar letters, and that the LBL compensatory strategy allows them to extract higher spatial frequencies. The LBL strategy would thus increase the spatial resolution of the visual system, effectively resolving the issue pertaining to between-letter similarity. In Experiments 1 and 2, we succeeded in replicating the main features characterizing LBL dyslexia by having normal individuals read low-contrast, high-pass-filtered words. Experiment 3, conducted in LBL dyslexic L.H., shows that, indeed, the letter confusability effect is based on low spatial frequencies, whereas this effect was not supported by high spatial frequencies.
Lapses in a Prefrontal-Extrastriate Preparatory Attention Network Predict Mistakes
Authors: Padilla Mayra L. , Wood Richard A. , Hale Laura A. , Knight Robert T.
Published: September 2006

Mistakes are common to all forms of behavior but there is disagreement about what causes errors. We recorded electrophysiological and behavioral measures in a letter discrimination task to examine whether deficits in preparatory attention predicted subsequent response errors. Error trials were characterized by decreased frontal-central preparatory attention event-related potentials (ERPs) prior to stimulus presentation and decreased extrastriate sensory ERPs during visual processing. These findings indicate that transient lapses in a prefrontal-extrastriate preparatory attention network can lead to response errors.
Specificity of Action Representations in the Lateral Occipitotemporal Cortex
Authors: Kable Joseph W. , Chatterjee Anjan
Published: September 2006

The ability to recognize actions is important for cognitive development and social cognition. Areas in the lateral occipitotemporal cortex show increased activity when subjects view action sequences; however, whether this activity distinguishes between specific actions as necessary for action recognition is unclear. We used a functional magnetic resonance imaging adaptation paradigm to test for brain regions that exhibit action-specific activity. Subjects watched a series of action sequences in which the action performed or the person performing the action could be repeated from a previous scan. Three regions—the superior temporal sulcus (pSTS), human motion-sensitive cortex (MT/MST), and extrastriate body area (EBA)—showed decreased activity for previously seen actions, even when the actions were novel exemplars because the persons involved had not been seen previously. These action-specific adaptation effects provide compelling evidence that representations in the pSTS, MT/MST, and EBA abstract actions from the agents involved and distinguish between different particular actions.
Processing of Musical Syntax Tonic versus Subdominant: An Event-related Potential Study
Authors: Poulin-Charronnat Bénédicte , Bigand Emmanuel , Koelsch Stefan
Published: September 2006

The present study investigates the effect of a change in syntactic-like musical function on event-related brain potentials (ERPs). Eight-chord piano sequences were presented to musically expert and novice listeners. Instructed to watch a movie and to ignore the musical sequences, the participants had to react when a chord was played with a different instrument than the piano. Participants were not informed that the relevant manipulation was the musical function of the last chord (target) of the sequences. The target chord acted either as a syntactically stable tonic chord (i.e., a C major chord in the key of C major) or as a less syntactically stable subdominant chord (i.e., a C major chord in the key of G major). The critical aspect of the results related to the impact such a manipulation had on the ERPs. An N5-like frontal negative component was found to be larger for subdominant than for tonic chords and attained significance only in musically expert listeners. These findings suggest that the subdominant chord is more difficult to integrate with the previous context than the tonic chord (as indexing by the observed N5) and that the processing of a small change in musical function occurs in an automatic way in musically expert listeners. The present results are discussed in relation to previous studies investigating harmonic violations with ERPs.
The Role of the Striatum in Processing Language Rules: Evidence from Word Perception in Huntington's Disease
Authors: Teichmann Marc , Dupoux Emmanuel , Kouider Sid , Bachoud-Lévi Anne-Catherine
Published: September 2006

On the assumption that linguistic faculties reflect both lexical storage in the temporal cortex and combinatorial rules in the striatal circuits, several authors have shown that striatal-damaged patients are impaired with conjugation rules while retaining lexical knowledge of irregular verbs [Teichmann, M., Dupoux, E., Kouider, S., Brugières, P., Boissé, M. F., Baudic, S., Cesaro, P., Peschanski, M., & Bachoud-Lévi, A. C. (2005). The role of the striatum in rule application. The model of Huntington's disease at early stage. Brain, 128, 1155–1167; Ullman, M. T., Corkin, S., Coppola, M., Hickok, G., Growdon, J. H., Koroshetz, W. J., & Pinker, S. (1997). A neural dissociation within language: Evidence that the mental dictionary is part of declarative memory, and that grammatical rules are processed by the procedural system. Journal of Cognitive Neuroscience, 9, 266–276]. Yet, such impairment was documented only with explicit conjugation tasks in the production domain. Little is known about whether it generalizes to other language modalities such as perception and whether it refers to implicit language processing or rather to intentional rule operations through executive functions. We investigated these issues by assessing perceptive processing of conjugated verb forms in a model of striatal dysfunction, namely, in Huntington's Disease (HD) at early stages. Rule application and lexical processes were evaluated in an explicit task (acceptability judgments on verb and nonword forms) and in an implicit task (lexical decision on frequency-manipulated verb forms). HD patients were also assessed in executive functions, and striatal atrophy was evaluated with magnetic resonance imaging (bicaudate ratio). Results from both tasks showed that HD patients were selectively impaired for rule application but lexical abilities were spared. Bicaudate ratios correlated with rule scores on both tasks, whereas executive parameters only correlated with scores on the explicit task. We argue that the striatum has a core function in linguistic rule application generalizing to perceptive aspects of morphological operations and pertaining to implicit language processes. In addition, we suggest that the striatum may enclose computational circuits that underpin explicit manipulation of regularities.
Neuroanatomical Evidence for Distinct Cognitive and Affective Components of Self
Authors: Moran J. M. , Macrae C. N. , Heatherton T. F. , Wyland C. L. , Kelley W. M.
Published: September 2006

This study examines whether the cognitive and affective components of self-reflection can be dissociated using functional magnetic resonance imaging. Using a simple paradigm in which subjects judged the personal relevance of personality characteristics that were either favorable (e.g., “honest”) or unfavorable (e.g., “lazy”, we found that distinct neural circuits in adjacent regions of the prefrontal cortex subserve cognitive and emotional aspects of self-reflection. The medial prefrontal cortex responded only to material that was self-descriptive, and this did not differ as a function of the valence of the trait. When material was judged to be self-relevant, the valence of the material was resolved in an adjacent region of ventral anterior cingulate. The nature of self is one of the most enduring questions in science, and researchers are now beginning to be able to decompose the neural operations that give rise to a unitary sense of self.