bluuebunny/crossref_metadata_2025 huggingface dataset:
Global Health Assistance: A New Perspective
Authors: Greenberg Henry M. , Farmer Richard G.
Published: October 2006

Health care priorities for many emerging economies have undergone a dramatic transition in the recent past because of the rise in chronic illness, increased longevity, and lessened infant mortality. Two additional major societal forces, democratization and the information revolution, will alter the nature of global health assistance. Because of democratization, governments will feel increasing pressure to provide adequate health care. Because of the information revolution, all practitioners will know what is available. The convergence of these three forces will create an enormous financial burden for emerging economies. Adapting to these new realities will be the challenge to donor organizations. What is likely to emerge as a critical health care problem around the world is the need to balance priorities between acute care and prevention or modification of chronic disease. These efforts will be directed at different populations, one manifestly ill and one potentially so, and each will need to be recognized politically as having valid claims on governmental resources. External support will need to include demonstration within the recipient communities that data collection permits an accurate identification of disease burden, that risk factor modification ameliorates the impact of disease, that continuity of care is essential to long term outcomes, and that therapy of developed disease can be rationally carried out utilizing evidence based medicine to insure efficiency and appropriateness. A.N.E. 2002;7(1):73–77
Differentiation of Narrow QRS Complex Tachycardia Types Using the 12‐Lead Electrocardiogram
Authors: Erdinler Izzet , Okmen Ertan , Oguz Enis , Akyol Ahmet , Gurkan Kadir , Ulufer Tanju
Published: October 2006

Background: Previous studies have shown that only 80% of narrow QRS supraventricular tachycardia (SVT) types can be differentiated by standard 12‐lead electrocardiographic (ECG) criteria. This study was designed to determine the value of some new ECG criteria in differentiating narrow QRS SVT.

Methods and Results : 120 ECGs demonstrating paroxysmal narrow QRS complex tachycardia (QRS s 0.11 ms and rate > 120 beats/min) were analyzed. Forty atrioventricular reciprocating tachycardia (AVRT), 70 atrioventricular nodal reentrant tachycardia (AVNRT), and 10 atrial tachycardia defined with electrophysiologic study (EPS) consisted the study group. Eight surface ECG criteria were found to be significantly different between tachycardia types by univariate analysis. P waves separate from the QRS complex were observed more frequently in AVRT (70%) and atrial tachycardia (80%). Pseudo r’deflection in lead V1, pseudo S wave in inferior leads, and cycle length alternans were more common in AVNRT (55, 20, and 6%, respectively). QRS alternans was also present during AVRT (28%). ST‐segment depression (≧ 2 mm) or T‐wave inversion, or both, were present more often in AVRT (60%) than in AVNRT (27%). During sinus rhythm, manifest preexcitation was observed more often in patients with AVRT (42%). When a P wave was present, RP/PR interval ratio > 1 was more common in atrial tachycardia (90%). By multivariate analysis, presence of a P wave separate from the QRS complex, pseudo r’deflection in lead V1, QRS alternans, preexcitation during sinus rhythm, ST‐segment depression > 2 mm or T‐wave inversion, or both, were independent predictors of tachycardia type.

Conclusions: Several new ECG criteria may be useful in differentiation of SVT types. Prediction of mechanism prior to EPS may provide additional benefits concerning the fluoroscopic exposure time and cardiac catheterization procedure. A.N.E. 2002;7(2):120–126
Location and Clinical Implications of High‐Degree Atrioventricular Block During Dipyridamole Infusion: A Case Report
Authors: Alakhras Mazen , Baldari Duccio , El‐Sherif Nabil , Turitto Gioia
Published: October 2006

We describe a patient with bifascicular block, who developed transient high‐degree atrioventricular block during dipyridamole infusion. This patient was subsequently found to have significant His‐Purkinje disease at electrophysiology study, and underwent permanent pacemaker implantation. Spontaneous atrioventricular block was documented during follow‐up. This case report raises the issue of dipyridamole safety in patients with intraventricular conduction defects, and contributes an additional mechanism to the possible explanation of dipyridamole‐induced atrioventricular block. A.N.E. 2002;7(2):174–176
Computerized Vectorcardiography Telemetry: A New Device for Continuous Multilead ST‐Segment Monitoring of Ambulatory Patients. A Preliminary Report
Authors: Nørgaard Bjarne Linde , Sørensen Claus , Larsen Thomas , Thygesen Kristian , Dellborg Mikael
Published: October 2006

Background: Continuous vectorcardiography ST‐segment monitoring has become a well‐established method in the surveillance of patients with acute myocardial ischemia. However, immobility of the vectorcardiography technique prevents monitoring of patients during ambulatory activities. Computerized vectorcardiography telemetry (CVT) with the capacity of real‐time ST‐segment analysis has been developed in an attempt to overcome this shortcoming. Recent data, however, indicate that changes in body position occasionally lead to pseudo‐ischemic ST‐segment changes during continuous ST‐segment monitoring.

Aims: This report describes the technical features of the CVT system, presents clinical examples using CVT, and assesses the influence of changes in body position on ST‐vector magnitude (ST‐VM) during CVT, respectively.

Methods: Clinical cases involving CVT are presented. The influence of changing body position during CVT monitoring was evaluated on 24 patients with suspected acute coronary syndromes, i.e., unstable angina or acute myocardial infarction. Each patient performed a specific body positional schedule.

Results: We present three discrete clinical cases where CVT provided early and valuable evidence of ongoing myocardial ischemia. The consequences of different recumbent and ambulatory body positions on ST‐VM during CVT monitoring appear to be limited.

Conclusion: Computerized vectorcardiography telemetry is a promising new tool for disclosing residual myocardial ischemic activity during the mobilization phase of patients with acute coronary syndromes. The clinical value of CVT needs further investigation in future trials. A.N.E. 2002;7(3):204–210
Sensitivity of Rhythm Disturbance Detection by Community Hospital Telemetry
Authors: Peterson Michael C. , Whetten Douglas K. , Renlund Dale G. , Coletti Andrew
Published: October 2006

Telemetry is done in a variety of settings with different levels of sophistication. The American College of Cardiology has made suggestions for telemetry monitoring but these are not in place in many smaller community hospitals that do telemetry monitoring. The objective of this study was to compare prospectively telemetry without a dedicated monitor watcher or full disclosure to results obtained on full disclosure. Patients included were admitted to a single community hospital with an indication for telemetry as judged by their primary physician. Telemetry results reported by the hospital staff were compared to over‐read of full disclosure traces by an academic cardiology service and the patient was used as his own control. Significant rhythm disturbances including pauses of 2 seconds or greater and short runs of ventricular and supraventricular tachycardia were frequently missed when a dedicated monitor watcher and full disclosure were not in use. When a dedicated monitor watcher and full disclosure are not in use, telemetry results should be accepted with caution and attempts should be made to improve monitoring. A.N.E. 2002;7(3):219–221 telemetry; full disclosure; dedicated monitor watcher
Age and Sex as Determinants of Ventricular Arrhythmic Events in Patients with Decompensated Congestive Heart Failure
Authors: Burger Andrew J. , Aronson Doron
Published: October 2006

Background: The propensity to develop specific arrhythmias varies between the sexes and is influenced by age. Patients with congestive heart failure (CHF) have a high prevalence of ventricular ectopy. However, in the setting of CHF, it is not known whether sex‐related or age‐dependent differences exist in the susceptibility to arrhythmias.

Methods: The study population included 134 men and 73 women (mean age 61 ± 14 years) admitted for decompensated CHF. The severity of ventricular arrhythmias was assessed by 24‐hour Holter monitoring. None of the patients were on parenteral vasoactive therapy during Holter recording.

Results: All measures of ventricular ectopy were markedly lower in women. The average hourly premature ventricular contractions (PVCs), the frequency of ventricular pairs, the mean hourly repetitive ventricular beats, and the frequency of ventricular tachycardia episodes per 24 hours were 40%, 62%, 65%, and 78% lower in women, respectively. Multivariate logistic regression revealed that the risk of developing > 3 ventricular pairs per 24‐hour period (OR = 2.2, Cl = 1.1–4.2, P = 0.03), > 3 repetitive ventricular beats/hour (OR = 2.5, Cl = 1.2–5.3, P = 0.01), or an episode of ventricular tachycardia (OR = 2.1, CI = 1.2–3.9, P = 0.01) were significantly higher in men. Patients in the higher fertile age group had a higher risk for the presence of > 3 ventricular pairs per 24‐hour period (OR = 2.3, CI = 1.1–4.2, P = 0.03), and the presence of > 3 repetitive ventricular beats per hour (OR = 5.9, CI = 2.7–13.3, P < 0.0001), compared with patients in the lower age fertile.

Conclusion: Male sex and age are associated with complex ventricular ectopy in patients with CHF. Further understanding of the mechanisms involved in the relative protection conferred by female sex would advance our understanding about arrhythmias in heart failure. A.N.E. 2002;7(3):234–241
Influence of Atropine on Fractal and Complexity Measures of Heart Rate Variability
Authors: Perkiomaki Juha S. , Zareba Wojciech , Badilini Fabio , Moss Arthur J.
Published: October 2006

Background: Measurement of short‐term fractal‐like correlation properties of heart rate dynamics has been shown to be a useful prognostic indicator of adverse events in cardiac patients. Complexity measurements of heart rate variability (HRV) have already provided important information in many cardiac conditions. However, data on the physiological background of these newer nonlinear measures of HRV are limited.

Methods: Nine healthy subjects (aged from 22 to 35 years, 6 males, 3 females) had an electro‐cardiographic (ECG) recording during controlled breathing in supine position. HRV was analyzed for 5 min periods before and after intravenous injection of 0.6 mg of atropine using conventional HRV measures and newer nonlinear HRV measures including the short‐term scaling exponent (a,) and approximate entropy (ApEn).

Results: The short‐term scaling exponent a1 increased significantly after atropine injection (1.01 ± 0.23 vs 1.43 ± 0.19, P = 0.001). There was no significant difference between ApEn values before and after atropine injection (0.87 ± 0.17 vs 0.70 ± 0.31, respectively, P = 0.27). At baseline before atropine administration, a1 had a significant negative correlation with SDNN, RMSSD, and HF (r = ‐0.70, ‐0.76, ‐0.67, respectively, P <0.05 for all), and a significant positive correlation with heart rate (r = 0.76, P < 0.05). After atropine injection, a, did not have significant correlation with any of the HRV parameters or heart rate. There were no significant correlations between ApEn and any of the HRV measures or heart rate either before or after atropine administration.

Conclusions: Vagal tone has an important influence on the values of the short‐term scaling exponent a,. However, vagal modulation is not a major determinant of the values of ApEn. A.N.E. 2002;7(4):326–331
Effect of Hollow Spherical Powder Size Distribution on Porosity and Segmentation Cracks in Thermal Barrier Coatings
Authors: Guo H. B. , Murakami H. , Kuroda S.
Published: October 2006

The effect of characteristics of hollow spherical (HOSP) powders on porosity and development of segmentation cracks in plasma‐sprayed thick thermal barrier coatings (TBCs) was investigated. Three powders with particle size ranges of 20–45, 53–75, and 90–120 μm were selected from a commercial HOSP powder feedstock for spraying the TBCs. The 20–45 μm powder has a higher deposition efficiency and a greater capability of producing segmented coatings than the other larger powders. Diagnostics of in‐flight particles show that the average surface temperature and velocity of the particles sprayed from the fine powder is higher by 250°C and 50 m/s compared with those sprayed from the 90 to 120 μm powder, respectively, due to its greater ratio of surface area to mass. The lower porosity of the coating sprayed from the fine powder is mainly attributed to the decreased volume of intersplat gaps and voids.
Covalently Connected Particles in Green Bodies Fabricated by Tape Casting
Authors: Duran Cihangir , Sato Kimiyasu , Hotta Yuji , Watari Koji
Published: October 2006

A novel approach is proposed to connect ceramic particles by means of organic covalent bonding in the green state. SiO2 particles coated with 3‐aminopropyltriethoxysilane were covalently bonded upon heating to 100°C, using polycarbodiimide in samples prepared by water‐based tape casting. The samples were dried at 100°C for 1 or 6 days and then soaked in water for shape stability and organic dissolution. Infrared measurements showed that organic covalent bonding was complete after drying for 6 days. This sample retained its shape perfectly after the soaking experiment in contrast to a green sample not heat treated at 100°C, which disintegrated very fast upon soaking. Thermogravimetric runs showed that the water‐soaked sample lost less weight as compared with samples not water soaked, showing that polymers from the green bodies could be removed without distorting the shape by the organic covalent bonding mechanism.
Influence of a Ceramic Substrate on Aqueous Precipitation and Structural Evolution of Alumina Nano‐Crystalline Coatings
Authors: Mahé Marie , Reynders Peter , Demourgues Alain , Heintz Jean‐Marc
Published: October 2006

Either boehmite (γ‐AlOOH) or gibbsite (γ‐Al(OH)3) nanocrystalline thin films (h≈100 nm) can be precipitated from AlCl3 solution at fixed pH and temperature onto different substrates. It depends on the nature of the substrate (mica flakes, SiO2 flakes, or α‐Al2O3 flakes), on their crystallographic properties (crystalline or amorphous), and on some experimental parameters (agitation rate, addition rate). According to the surface charge of the substrates, different alumina species are involved in the precipitation process. When negative charges are present on the substrate, the [Al3O(OH)3(OH2)9]4+ polycation is promoted, leading to the formation of the (Al4) tetramer ([Al4O(OH)10(OH2)5]o) and then to the precipitation of bohemite. When positive charges are present, a ligand bridge containing complex ([Al3O(OH)3(O2H3)3(OH2)9]+) is likely favored, giving rise to hexagonal ring structures or amorphous solids that lead to the formation of gibbsite. Besides the surface effects, crystalline substrates can act as a template during precipitation of aluminum species as shown for the formation of gibbsite on muscovite. Finally, calcination at 850°C of boehmite samples leads to porous γ‐Al2O3 layers, while calcination of gibbsite leads to δ‐Al2O3 layers.
Mitochondrial affinity for ADP is twofold lower in creatine kinase knock‐out muscles
Authors: ter Veld Frank , Jeneson Jeroen A. L. , Nicolay Klaas
Published: October 2006

Adaptations of the kinetic properties of mitochondria in striated muscle lacking cytosolic (M) and/or mitochondrial (Mi) creatine kinase (CK) isoforms in comparison to wild‐type (WT) were investigated in vitro. Intact mitochondria were isolated from heart and gastrocnemius muscle of WT and single‐ and double CK‐knock‐out mice strains (cytosolic (M‐CK–/–), mitochondrial (Mi‐CK–/–) and double knock‐out (MiM‐CK–/–), respectively). Maximal ADP‐stimulated oxygen consumption flux (State3 Vmax; nmol O2·mg mitochondrial protein−1·min−1) and ADP affinity (; µm) were determined by respirometry. State 3 Vmax and of M‐CK–/– and MiM‐CK–/– gastrocnemius mitochondria were twofold higher than those of WT, but were unchanged for Mi‐CK–/–. For mutant cardiac mitochondria, only the of mitochondria isolated from the MiM‐CK–/– phenotype was different (i.e. twofold higher) than that of WT. The implications of these adaptations for striated muscle function were explored by constructing force‐flow relations of skeletal muscle respiration. It was found that the identified shift in affinity towards higher ADP concentrations in MiM‐CK–/– muscle genotypes may contribute to linear mitochondrial control of the reduced cytosolic ATP free energy potentials in these phenotypes.
Structural determinants of protein stabilization by solutes
Authors: Pais Tiago M. , Lamosa Pedro , dos Santos Wagner , LeGall Jean , Turner David L. , Santos Helena
Published: October 2006

Despite their high sequence homology, rubredoxins from Desulfovibrio gigas and D. desulfuricans are stabilized to very different extents by compatible solutes such as diglycerol phosphate, the major osmolyte in the hyperthermophilic archaeon Archaeoglobus fulgidus[Lamosa P, Burke A, Peist R, Huber R, Liu M Y, Silva G, Rodrigues‐Pousada C, LeGall J, Maycock C and Santos H (2000) Appl Environ Microbiol66, 1974–1979]. The principal structural difference between these two proteins is the absence of the hairpin loop in the rubredoxin from D. desulfuricans. Therefore, mutants of D. gigas rubredoxin bearing deletions in the loop region were constructed to investigate the importance of this structural feature on protein intrinsic stability, as well as on its capacity to undergo stabilization by compatible solutes. The three‐dimensional structure of the mutant bearing the largest deletion, Δ17|29, was determined by 1H‐NMR, demonstrating that, despite the drastic deletion, the main structural features were preserved. The dependence of the NH chemical shifts on temperature and solute concentration (diglycerol phosphate or mannosylglycerate) provide evidence of subtle conformational changes induced by the solute. The kinetic stability (as assessed from the absorption decay at 494 nm) of six mutant rubredoxins was determined at 90 °C and the stabilizing effect exerted by both solutes was assessed. The extent of protection conferred by each solute was highly dependent on the specific mutant examined: while the half‐life for iron release in the wild‐type D. gigas rubredoxin increased threefold in the presence of 0.1 m diglycerol phosphate, mutant Δ23|29 was destabilized. This study provides evidence for solute‐induced compaction of the protein structure and occurrence of weak, specific interactions with the protein surface. The relevance of these findings to our understanding of the molecular basis for protein stabilization is discussed.
The stop transfer sequence of the human UDP‐glucuronosyltransferase 1A determines localization to the endoplasmic reticulum by both static retention and retrieval mechanisms
Authors: Barré Lydia , Magdalou Jacques , Netter Patrick , Fournel‐Gigleux Sylvie , Ouzzine Mohamed
Published: October 2006

Human UDP‐glucuronosyltransferase 1A (UGT1A) isoforms are endoplasmic reticulum (ER)‐resident type I membrane proteins responsible for the detoxification of a broad range of toxic phenolic compounds. These proteins contain a C‐terminal stop transfer sequence with a transmembrane domain (TMD), which anchors the protein into the membrane, followed by a short cytosolic tail (CT). Here, we investigated the mechanism of ER residency of UGT1A mediated by the stop transfer sequence by analysing the subcellular localization and sensitivity to endoglycosidases of chimeric proteins formed by fusion of UGT1A stop transfer sequence (TMD/CT) with the ectodomain of the plasma membrane CD4 reporter protein. We showed that the stop transfer sequence, when attached to C‐terminus of the CD4 ectodomain was able to prevent it from being transported to the cell surface. The protein was retained in the ER indicating that this sequence functions as an ER localization signal. Furthermore, we demonstrated that ER localization conferred by the stop transfer sequence was mediated in part by the KSKTH retrieval signal located on the CT. Interestingly, our data indicated that UGT1A TMD alone was sufficient to retain the protein in ER without recycling from Golgi compartment, and brought evidence that organelle localization conferred by UGT1A TMD was determined by the length of its hydrophobic core. We conclude that both retrieval mechanism and static retention mediated by the stop transfer sequence contribute to ER residency of UGT1A proteins.
A near-infrared spectroscopic detection of the brown dwarf in the post common envelope binary WD 0137-349
Authors: Burleigh M. R. , Hogan E. , Dobbie P. D. , Napiwotzki R. , Maxted P. F. L.
Published: October 2006

We present a near-infrared spectrum of the close, detached white dwarf + brown dwarf binary WD 0137-349, which directly reveals the substellar companion through an excess of flux longwards of ≈1.95 μm. We best match the data with a white dwarf + L8 composite model. For ages ∼1 Gyr, the spectral type of the cool secondary is in agreement with the mass determined by Maxted et al. from radial velocity measurements (0.053 ± 0.006 M⊙), and supports an evolutionary scenario in which the brown dwarf survived a previous phase of common envelope evolution which resulted in the formation of this close binary. The brown dwarf is the lowest mass companion to a white dwarf yet found, and the lowest mass object known to have survived a common envelope phase. At 1300 < Teff < 1400 K WD 0137-349B is also the coolest known companion to a white dwarf. At a separation a= 0.65 R⊙ the hemisphere of the brown dwarf facing the 16 500 K white dwarf is being heated through irradiation. We discuss the possible effects of this additional heating, with particular relevance to those other close binaries with substellar companions, the hot Jupiters. We propose future observations to investigate the likely temperature differences between the ‘day’ and ‘night’ sides of the brown dwarf.
The sigma‐1 receptor modulates NMDA receptor synaptic transmission and plasticity via SK channels in rat hippocampus
Authors: Martina Marzia , Turcotte Marie‐Eve B. , Halman Samantha , Bergeron Richard
Published: October 2006

The sigma receptor (σR), once considered a subtype of the opioid receptor, is now described as a distinct pharmacological entity. Modulation ofN‐methyl‐d‐aspartate receptor (NMDAR) functions by σR‐1 ligands is well documented; however, its mechanism is not fully understood. Using patch‐clamp whole‐cell recordings in CA1 pyramidal cells of rat hippocampus and (+)pentazocine, a high‐affinity σR‐1 agonist, we found that σR‐1 activation potentiates NMDAR responses and long‐term potentiation (LTP) by preventing a small conductance Ca2+‐activated K+current (SK channels), known to shunt NMDAR responses, to open. Therefore, the block of SK channels and the resulting increased Ca2+influx through the NMDAR enhances NMDAR responses and LTP. These results emphasize the importance of the σR‐1 as postsynaptic regulator of synaptic transmission.
Synaptic kainate currents reset interneuron firing phase
Authors: Yang Ellen J. , Harris Alexander Z. , Pettit Diana L.
Published: October 2006

Hippocampal interneuron activity has been linked to epileptogenesis, seizures and the oscillatory synaptic activity detected in behaving rats. Interneurons fire at specific times in the rhythmic cycles that comprise these oscillations; however, the mechanisms controlling these firing patterns remain unclear. We have examined the role of synaptic input in modulating the firing of spontaneously active rat hippocampal interneurons. We find that synaptic glutamate receptor currents of 20–30 pA increase instantaneous firing frequency and reset the phase of spontaneously firing CA1 stratum oriens interneurons. Kainate receptor (KAR)‐mediated currents are particularly effective at producing this phase reset, while AMPA receptor currents are relatively ineffective. The efficacy of KAR‐mediated currents is probably due to their 3‐fold longer decay. Given the small amplitude of the currents needed for this phase reset, coincident activation of only a few KAR‐containing synapses could synchronize firing in groups of interneurons. These data suggest that KARs are potent modulators of circuit behaviour and their activation alters hippocampal interneuron output.
Repeated maternal glucocorticoid treatment affects activity and hippocampal NMDA receptor expression in juvenile guinea pigs
Authors: Owen Dawn , Matthews Stephen G.
Published: October 2006

The behavioural consequences of prenatal glucocorticoid exposure are not well understood, though emerging studies in humans indicate hyperactivity and altered cognitive development can occur. Further, recent reports indicate that N‐methyl‐d‐aspartate receptors (NMDARs) may mediate the development of postnatal stress behaviours. We hypothesized that prenatal betamethasone (Beta) administration would alter behaviour and the expression of hippocampal NMDAR subunits NR1, NR2A and NR2B in juvenile guinea pig offspring. We found that repeated maternal Beta (1 mg kg−1) treatment on gestational days (gd) 40/41, 50/51 and 60/61 (term∼70 days) had no significant effect on birthweight or early growth. However, Beta produced sex‐specific effects on open‐field activity and hippocampal NMDAR subunit expression compared with controls. Female Beta offspring exhibited significantly increased locomotor activity while there was no effect in Beta males. Beta males exhibited a tendency for decreased anxiety‐like behaviour. With respect to NMDAR subunit expression, Beta‐exposed females exhibited significantly reduced NR1 mRNA in CA1/2 and CA3 subfields of the hippocampus; there were no effects in Beta males. In conclusion, repeated maternal treatment with Beta, in a similar regimen to that administered to pregnant women at risk of delivering preterm, has profound consequences on behaviour and development of crucial neurotransmitter systems in postnatal life.
Selectivity of End-Cretaceous Marine Bivalve Extinctions
Authors: Jablonski David , Raup David M.
Published: October 2006

Analyses of the end-Cretaceous or Cretaceous-Tertiary mass extinction show no selectivity of marine bivalve genera by life position (burrowing versus exposed), body size, bathymetric position on the continental shelf, or relative breadth of bathymetric range. Deposit-feeders as a group have significantly lower extinction intensities than suspension-feeders, but this pattern is due entirely to low extinction in two groups (Nuculoida and Lucinoidea), which suggests that survivorship was not simply linked to feeding mode. Geographically widespread genera have significantly lower extinction intensities than narrowly distributed genera. These results corroborate earlier work suggesting that some biotic factors that enhance survivorship during times of lesser extinction intensities are ineffectual during mass extinctions.
Solar Neutrinos—From Puzzle to Paradox
Authors: Raghavan R. S.
Published: October 2006

The solar neutrino puzzle is deepening into a paradox that refutes the basic logic of the reaction chain that powers the sun by the fusion of protons into heavy elements. Experiments now reveal a serious anomaly in the relative neutrino fluxes from the different steps in the chain. Neutrinos from boron-8 at the end of the chain are seen but hardly any are seen from beryllium-7, without which the observed boron-8 cannot be made. The only apparent way to avoid a paradoxical "missing link" in the sun's energy chain is a nonzero neutrino mass, an idea that can be tested in future experiments.
High-Luminosity Blue and Blue-Green Gallium Nitride Light-Emitting Diodes
Authors: Morkoç H. , Mohammad S. N.
Published: October 2006

Compact and efficient sources of blue light for full color display applications and lighting eluded and tantalized researchers for many years. Semiconductor light sources are attractive owing to their reliability and amenability to mass manufacture. However, large band gaps are required to achieve blue color. A class of compound semiconductors formed by metal nitrides, GaN and its allied compounds AIGaN and InGaN, exhibits properties well suited for not only blue and blue-green emitters, but also for ultraviolet emitters and detectors. What thwarted engineers and scientists from fabricating useful devices from these materials in the past was the poor quality of material and lack of
p
-type doping. Both of these obstacles have recently been overcome to the point where high-luminosity blue and blue-green light-emitting diodes are now available in the marketplace.
Oscillating Stereocontrol: A Strategy for the Synthesis of Thermoplastic Elastomeric Polypropylene
Authors: Coates Geoffrey W. , Waymouth Robert M.
Published: October 2006

A strategy has been developed for the synthesis of thermoplastic elastomeric polypropylene based on the catalytic activity of the unbridged metallocene bis(2-phenylindenyl)zirconium dichloride [(2-PhInd)
2
ZrCl
2
]. This catalyst was designed to isomerize between achiral and chiral coordination geometries during the polymerization reaction to produce atactic-isotactic stereoblock polymers. The metallocene precursor (2-PhInd)
2
ZrCl
2
in the presence of methylaluminoxane polymerizes propylene to yield rubbery polypropylene. The isotacticity of the polymer, described by the isotactic pentad content, increases with increasing propylene pressure and decreasing polymerization temperature to produce polypropylenes with an isotactic pentad content ranging from 6.3 to 28.1 percent.
High-Rate, Gas-Phase Growth of MoS
2
Nested Inorganic Fullerenes and Nanotubes
Authors: Feldman Y. , Wasserman E. , Srolovitz D. J. , Tenne R.
Published: October 2006

The gas-phase reaction between MoO

3-
x

and H
2
S in a reducing atmosphere at elevated temperatures (800° to 950°C) has been used to synthesize large quantities of an almost pure nested inorganic fullerene (IF) phase of MoS
2
. A uniform IF phase with a relatively narrow size distribution was obtained. The synthesis of IFs appears to require, in addition to careful control over the growth conditions, a specific turbulent flow regime. The x-ray spectra of the different samples show that, as the average size of the IF decreases, the van der Waals gap along the
c
axis increases, largely because of the strain involved in folding of the lamella. Large quantities of quite uniform nanotubes were obtained under modified preparation conditions.
Metabolic Engineering of a Pentose Metabolism Pathway in Ethanologenic
Zymomonas mobilis
Authors: Zhang Min , Eddy Christina , Deanda Kristine , Finkelstein Mark , Picataggio Stephen
Published: October 2006

The ethanol-producing bacterium
Zymomonas mobilis
was metabolically engineered to broaden its range of fermentable substrates to include the pentose sugar xylose. Two operons encoding xylose assimilation and pentose phosphate pathway enzymes were constructed and transformed into
Z. mobilis
in order to generate a strain that grew on xylose and efficiently fermented it to ethanol. Thus, anaerobic fermentation of a pentose sugar to ethanol was achieved through a combination of the pentose phosphate and Entner-Doudoroff pathways. Furthermore, this strain efficiently fermented both glucose and xylose, which is essential for economical conversion of lignocellulosic biomass to ethanol.
Photoemission Studies of High-
T
c
Superconductors: The Superconducting Gap
Authors: Shen Z. -X. , Spicer W. E. , King D. M. , Dessau D. S. , Wells B. O.
Published: October 2006

Over the last several years there have been great improvements in the energy resolution and detection efficiency of angle-resolved photoemission spectroscopy. These improvements have made it possible to discover a number of fascinating features in the electronic structure of the high transition temperature (
T
c
) superconductors: apparently bandlike Fermi surfaces, flat-band saddle points, and nested Fermi surface sections. Recent work suggests that these features, previously thought explainable only by one-electron band theory, may be better understood with a many-body approach. Furthermore, other properties of the high-
T
c
superconductors, which are difficult to understand with band theory, are well described using a many-body picture. Angle-resolved photoemission spectroscopy has also been used to investigate the nature of the superconducting pairing state, revealing an anisotropic gap consistent with a
d
-wave order parameter and fueling the current debate over
s
-wave versus
d
-wave superconductivity.
Mechanisms of Argon Retention in Clays Revealed by Laser
40
Ar-
39
Ar Dating
Authors: Dong Hailiang , Hall Chris M. , Peacor Donald R. , Halliday Alex N.
Published: October 2006

A method for dating clays is important for studies of weathering, diagenesis, hydrocarbon migration, and the formation of major metalliferous deposits. However, many attempts have produced imprecise or inaccurate results. Data from shales show that, contrary to expectations, the
40
Ar-
39
Ar dating technique can be successfully used to determine the diagenetic age of ancient sediments because
39
Ar losses during irradiation are controlled by release from low retentivity sites in illite equivalent to those that have lost radiogenic
40
Ar in nature, rather than by direct recoil as is generally assumed.
Absorption of Solar Radiation by Clouds: Observations Versus Models
Authors: Cess R. D. , Zhang M. H. , Minnis P. , Corsetti L. , Dutton E. G. , Forgan B. W. , Garber D. P. , Gates W. L. , Hack J. J. , Harrison E. F. , Jing X. , Kiehi J. T. , Long C. N. , Morcrette J. -J. , Potter G. L. , Ramanathan V. , Subasilar B. , Whitlock C. H. , Young D. F. , Zhou Y.
Published: October 2006

There has been a long history of unexplained anomalous absorption of solar radiation by clouds. Collocated satellite and surface measurements of solar radiation at five geographically diverse locations showed significant solar absorption by clouds, resulting in about 25 watts per square meter more global-mean absorption by the cloudy atmosphere than predicted by theoretical models. It has often been suggested that tropospheric aerosols could increase cloud absorption. But these aerosols are temporally and spatially heterogeneous, whereas the observed cloud absorption is remarkably invariant with respect to season and location. Although its physical cause is unknown, enhanced cloud absorption substantially alters our understanding of the atmosphere's energy budget.
At Math Meetings, Enormous Theorem Eclipses Fermat
Authors: Cipra Barry
Published: October 2006

Hardly a word was said about Fermat's Last Theorem at the joint meetings of the American Mathematical Society and the Mathematical Association of America, held this year from 4 to 7 January in San Francisco. For Andrew Wiles's proof, no news is good news: There are no reports of mistakes. But mathematicians found plenty of other topics to discuss. Among them: a computational breakthrough in the study of turbulent diffusion and progress in slimming down the proof of an important result in group theory, whose original size makes checking the proof of Fermat's Last Theorem look like an afternoon's pastime.
Temperature Dependence of the Superconducting Gap Anisotropy in Bi
2
Sr
2
CaCu
2
O
8+x
Authors: Ma Jian , Quitmann C. , Kelley R. J. , Berger H. , Margaritondo G. , Onellion M.
Published: October 2006

Detailed data on the momentum-resolved temperature dependence of the superconducting gap of Bi
2
Sr
2
CaCu
2
O
8+x
are presented, complemented by similar data on the intensity of the photoemission superconducting condensate spectral area. The gap anisotropy between the Γ-M̅ and Γ-X directions increases markedly with increasing temperature, contrary to what happens for conventional anisotropic-gap superconductors, such as lead. Specifically, the size of the superconducting gap along the Γ-X direction decreases to values indistinguishable from zero at temperatures for which the gap retains virtually full value along the Γ-M̅ direction. These data rule out the simplest type of
d
-wave order parameter.
Iceberg Discharges into the North Atlantic on Millennial Time Scales During the Last Glaciation
Authors: Bond Gerard C. , Lotti Rusty
Published: October 2006

High-resolution studies of North Atlantic deep sea cores demonstrate that prominent increases in iceberg calving recurred at intervals of 2000 to 3000 years, much more frequently than the 7000- to 10,000-year pacing of massive ice discharges associated with Heinrich events. The calving cycles correlate with warm-cold oscillations, called Dansgaard-Oeschger events, in Greenland ice cores. Each cycle records synchronous discharges of ice from different sources, and the cycles are decoupled from sea-surface temperatures. These findings point to a mechanism operating within the atmosphere that caused rapid oscillations in air temperatures above Greenland and in calving from more than one ice sheet.
The Case for a Hubble Constant of 30 km s
–1
Mpc
–1
Authors: Bartlett James G. , Blanchard Alain , Silk Joseph , Turner Michael S.
Published: October 2006

Although recent determinations of the distance to the Virgo cluster based on Cepheid variable stars represent an important step in pinning down the Hubble constant, after 65 years a definitive determination of the Hubble constant still eludes cosmologists. At present, most of the observational determinations place the Hubble constant between 40 and 90 kilometers per second per megaparsec (km s
–1
Mpc
–1
). The case is made here for a Hubble constant that is even smaller than the lower bound of the accepted range on the basis of the great advantages, all theoretical in nature, of a Hubble constant of around 30 kilometers per second per megaparsec. Such a value for the Hubble cures all of the ills of the current theoretical orthodoxy, that is, a spatially flat universe composed predominantly of cold dark matter.
Environmental and Economic Costs of Soil Erosion and Conservation Benefits
Authors: Pimentel David , Harvey C. , Resosudarmo P. , Sinclair K. , Kurz D. , McNair M. , Crist S. , Shpritz L. , Fitton L. , Saffouri R. , Blair R.
Published: October 2006

Soil erosion is a major environmental threat to the sustainability and productive capacity of agriculture. During the last 40 years, nearly one-third of the world's arable land has been lost by erosion and continues to be lost at a rate of more than 10 million hectares per year. With the addition of a quarter of a million people each day, the world population's food demand is increasing at a time when per capita food productivity is beginning to decline.
Prehistoric Extinctions of Pacific Island Birds: Biodiversity Meets Zooarchaeology
Authors: Steadman David W.
Published: October 2006

On tropical Pacific islands, a human-caused "biodiversity crisis" began thousands of years ago and has nearly run its course. Bones identified from archaeological sites show that most species of land birds and populations of seabirds on those islands were exterminated by prehistoric human activities. The loss of birdlife in the tropical Pacific may exceed 2000 species (a majority of which were species of flightless rails) and thus represents a 20 percent worldwide reduction in the number of species of birds. The current global extinction crisis therefore has historic precedent.
Near-Atomic Resolution Imaging of Ferroelectric Liquid Crystal Molecules on Graphite by STM
Authors: Walba David M. , Stevens Forrest , Parks Daniel C. , Clark Noel A. , Wand Michael D.
Published: October 2006

Near-atomic resolution images of a two-dimensional heteroepitaxial crystal composed of the relatively "functionally rich" chiral liquid crystal mesogen MDW 74 on graphite have been obtained by scanning tunneling microscopy (STM). This work is aimed at developing an improved understanding of the commercially crucial phenomenon of liquid crystal alignment by studying well-characterized surfaces. Herein is reported molecular-level characterization of the surface underlying a ferroelectric liquid crystal in situ, a requisite starting point for understanding the liquid crystal-solid interface at the molecular level. The results are also important in the context of developing a model for the molecular origins of the contrast observed in STM images of organic monolayers on conductor surfaces. The data and analysis provide strong evidence that neither frontier orbital alone (highest occupied or lowest unoccupied molecular orbital) is sufficient to describe the observed tunneling efficiency.
A Structure Model and Growth Mechanism for Multishell Carbon Nanotubes
Authors: Amelinckx S. , Bernaerts D. , Zhang X. B. , Van Tendeloo G. , Van Landuyt J.
Published: October 2006

A model that postulates a mixture of scroll-shaped and concentric, cylindrical graphene sheets is proposed to explain the microstructure of graphite multishell nanotubes grown by arc discharge. The model is consistent with the observed occurrence of a relatively small number of different chiral angles within the same tubule. The model explains clustering in a natural way and is consistent with the observation of asymmetric (0002) lattice fringe patterns and with the occurrence of singular fringe spacings larger than
c
/2 (
c
is the
c
parameter of graphite) in such patterns. Anisotropic thermal contraction accounts for the 2 to 3 percent increase in the
c
parameter of nanotubes, compared with bulk graphite, but is too small to explain the singular fringe spacings. The model also explains the formation of multishell closure domes. Nucleation is attributed to the initial formation of a fullerene "dome."
Biogeological Mineralization in Deep-Sea Hydrothermal Deposits
Authors: Cook Terri L. , Stakes Debra S.
Published: October 2006

Oriented drill cores retrieved from active massive sulfide edifices at the Endeavour Segment of the Juan de Fuca Ridge contain an abundance of fossilized tube structures associated with vestimentiferan and annelid worms. The petrological evolution of these biogeological structures and their presence deep inside the edifice walls demonstrate that an initial, worm-mediated texture directly affects the subsequent steps of inorganic precipitation, wall infilling, and outward growth of these black smoker deposits. The presence of fossilized structures in hydrothermal discharge sites that are 2 kilometers apart and their similarity to structures observed in other modern and ancient deposits suggest that these biogeological processes are general phenomena.
Organic Transistors: Two-Dimensional Transport and Improved Electrical Characteristics
Authors: Dodabalapur A. , Torsi L. , Katz H. E.
Published: October 2006

The thiophene oligomer α-hexathienylene (α-6T) has been successfully used as the active semiconducting material in thin-film transistors. Field-induced conductivity in thin-film transistors with α-6T active layers occurs only near the interfacial plane, whereas the residual conductivity caused by unintentional doping scales with the thickness of the layer. The two-dimensional nature of the field-induced conductivity is due not to any anisotropy in transport with respect to any molecular axis but to interface effects. Optimized methods of device fabrication have resulted in high field-effect mobilities and on/off current ratios of > 10
6
. The current densities and switching speeds are good enough to allow consideration of these devices in practical large-area electronic circuits.
Dwarfs and Dim Galaxies Mark Limits of Knowledge
Authors: Hellemans Alexander
Published: October 2006

When 250 astronomers met in Cardiff early this month at the U.K. National Astronomy Meeting, sponsored by the Royal Astronomical Society and the Particle Physics and Astronomy Research Council, they grappled with some big problems, among them the age of the universe and its mass. They also took on an even bigger metaproblem: How confident can they be in their knowledge about cosmic origins?
The Silica Balance in the World Ocean: A Reestimate
Authors: Tréguer Paul , Nelson David M. , Van Bennekom Aleido J. , DeMaster David J. , Leynaert Aude , Quéguiner Bernard
Published: October 2006

The net inputs of silicic acid (dissolved silica) to the world ocean have been revised to 6.1 ± 2.0 teramoles of silicon per year (1 teramole = 10
12
moles). The major contribution (about 80 percent) comes from rivers, whose world average silicic acid concentration is 150 micromolar. These inputs are reasonably balanced by the net ouputs of biogenic silica of 7.1 ± 1.8 teramoles of silicon per year in modern marine sediments. The gross production of biogenic silica (the transformation of dissolved silicate to particulate skeletal material) in surface waters was estimated to be 240 ± 40 teramoles of silicon per year, and the preservation ratio (opal accumulation in sediment/gross production in surface waters) averages 3 percent. In the world ocean the residence time of silicon, relative to total biological uptake in surface waters, is about 400 years.
Seismic Images of Active Magma Systems Beneath the East Pacific Rise Between 17°05′ and 17°35′S
Authors: Mutter John C. , Carbotte Suzanne M. , Su Wusi , Xu Liqing , Buhl Peter , Detrick Robert S. , Kent Graham M. , Orcutt John A. , Harding Alistair J.
Published: October 2006

Seismic reflection data from the East Pacific Rise between 17°05′ and 17°35′S image a magma lens that varies regularly in depth and width as ridge morphology changes, confirming the notion that axial morphology can be used to infer ridge magmatic state. However, at 17°26′S, where the ridge is locally shallow and broad, the magma lens is markedly shallower and wider than predicted from regional trends. In this area, submersible dives reveal recent volcanic eruptions. These observations indicate that it is where the width and depth of the magma chamber differ from regional trends, indicating an enhanced magmatic budget, that is diagnostic of current magmatism.
From Microwave Anisotropies to Cosmology
Authors: Scott Douglas , Silk Joseph , White Martin
Published: October 2006

Fluctuations in the temperature of the cosmic microwave background have now been detected over a wide range of angular scales, and a consistent picture seems to be emerging. This article describes some of the implications for cosmology. Analysis of all of the published detections suggests the existence of a peak on degree scales with a height 2.4 to 10 (90 percent confidence level) times the amplitude of the power spectrum at large angular scales. This result confirms an early prediction, implies that the universe did in fact recombine, and limits theories of structure formation. Illustrative examples show how comparison of the microwave background data and the large-scale structure data will be a potentially powerful means of answering fundamental questions about the universe.
Seismic Evidence for an Earthquake Nucleation Phase
Authors: Ellsworth W. L. , Beroza G. C.
Published: October 2006

Near-source observations show that earthquakes initiate with a distinctive seismic nucleation phase that is characterized by a low rate of moment release relative to the rest of the event. This phase was observed for the 30 earthquakes having moment magnitudes 2.6 to 8.1, and the size and duration of this phase scale with the eventual size of the earthquake. During the nucleation phase, moment release was irregular and appears to have been confined to a limited region of the fault. It was characteristically followed by quadratic growth in the moment rate as rupture began to propagate away from the nucleation zone. These observations suggest that the nucleation process exerts a strong influence on the size of the eventual earthquake.