bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling of the thermal state of Mount Vesuvius from 1631 A.D. to present and the role of CO2 degassing on the volcanic conduit closure after the 1944 A.D. eruption
Authors: Quareni Francesca , Moretti Roberto , Piochi Monica , Chiodini Giovanni
Published: February 2007

The last eruptive event at Mount Vesuvius occurred in 1944 A.D., ending a cycle of continuous eruptive activity started with the sub‐Plinian event of 1631 A.D. The aim of this research is (1) to model the thermal evolution of the volcanic system from 1631 A.D. up to the present and (2) to investigate the possible process leading the volcano to the current state of quiescence. A finite element software is employed to solve the time‐dependent energy equation and obtain the thermal field in the volcanic edifice and the surrounding medium. Volcanological, petrological, and geophysical constraints are used to define the crustal structure beneath the volcanic edifice, the magma supply system active since 1631 A.D., and the physico‐chemical conditions of magma. Thermodynamic properties of magma and wall rocks have been evaluated from well‐established thermo‐chemical compilations and data from the literature. It is shown that heat transfer due to magma degassing is required in addition to the heat conduction in order to obtain transient depth‐temperature fields consistent with geochemical observations, high crustal magnetization, and rigid behavior of the shallow crust as indicated by geophysical data. Surface data of carbon dioxide soil flux coming out from the Mount Vesuvius crater are taken to constrain such an additional heat flux. The agreement between modeled and measured temperatures at the crater since 1944 A.D. proves the consistency of the model. It is concluded that the present state of quiescence of Mount Vesuvius is mostly a consequence of the absence of magma supply from the deep reservoir into the shallower system. This allows the cooling of residual magma left within the volcanic conduit and the transition from continuous eruptive activity to the condition of conduit obstruction. In this scenario, the hydrothermal system may have developed subsequent to the cooling of the magma within the conduit. Our findings are a direct consequence of the high concentration of CO2 in the most mafic Vesuvian magmas: The low solubility of CO2, with respect to H2O, enables a high mass flux of carbon dioxide through the volcanic edifice. The results of this study are relevant for hazard assessment at Vesuvius and indicate directions for further investigation, such as the role of the hydrothermal system on the thermal energy budget of the volcanic system and its relationships with fluids released by crustal structures likely to host the magmatic reservoir. In general, the role of the high concentration of carbon dioxide in magmas should be more questioned and investigated when studying the behavior of volcanic systems, particularly in south Italy volcanoes.
Dynamic multiphase flow model of hydrate formation in marine sediments
Authors: Liu Xiaoli , Flemings Peter B.
Published: February 2007

We developed a multicomponent, multiphase, fluid and heat flow model to describe hydrate formation in marine sediments; the one‐ and two‐dimensional model accounts for the dynamic effects of hydrate formation on salinity, temperature, pressure, and hydraulic properties. Free gas supplied from depth forms hydrate, depletes water, and elevates salinity until pore water is too saline for further hydrate formation: Salinity and hydrate concentration increase upward from the base of the regional hydrate stability zone (RHSZ) to the seafloor, and the base of the hydrate stability zone has significant topography. In fine‐grained sediments, hydrate formation leads to rapid permeability reduction and capillary sealing to free gas. This traps gas and causes gas pressure to build up until it exceeds the overburden stress and drives gas through the RHSZ. Gas chimneys couple the free gas zone to the seafloor through high‐salinity conduits that are maintained at the three‐phase boundary by gas flow. As a result, significant amounts of gaseous methane can bypass the RHSZ, which implies a significantly smaller hydrate reservoir than previously envisioned. Hydrate within gas chimneys lies at the three‐phase boundary, and thus small increases in temperature or decreases in pressure can immediately transport methane into the ocean. This type of hydrate deposit may be the most economical for producing energy because it has very high methane concentrations (Sh > 70%), located near the seafloor, which lie on the three‐phase boundary.
Early exhumation of high‐pressure rocks in extrusion wedges: Cycladic blueschist unit in the eastern Aegean, Greece, and Turkey
Authors: Ring Uwe , Will Thomas , Glodny Johannes , Kumerics Christine , Gessner Klaus , Thomson Stuart , Güngör Talip , Monié Patrick , Okrusch Martin , Drüppel Kirsten
Published: February 2007

Structural, metamorphic, and geochronologic work shows that the Ampelos/Dilek nappe of the Cycladic blueschist unit in the eastern Aegean constitutes a wedge of high‐pressure rocks extruded during early stages of orogeny. The extrusion wedge formed during the incipient collision of the Anatolian microcontinent with Eurasia when subduction and deep underthrusting ceased and the Ampelos/Dilek nappe was thrust southward over the greenschist‐facies Menderes nappes along its lower tectonic contact, the Cycladic‐Menderes thrust, effectively cutting out a ∼30‐ to 40‐km‐thick section of crust. The upper contact of the Ampelos/Dilek extrusion wedge is the top‐to‐the‐NE Selçuk normal shear zone, along which the Ampelos/Dilek nappe was exhumed by ∼30–40 km. Detailed Rb‐Sr and 40Ar/39Ar dating of mylonites demonstrates that both shear zones operated between 42 and 32 Ma. There is no evidence for episodic motion during the ∼10 Myr life span of the shear zones, suggesting that both shear zones operated in a steady, nonepisodic fashion. Our data provide supporting evidence that simultaneous thrust‐type and normal sense shearing can accomplish the early exhumation of deep‐seated rocks.
Effects of seasonal changes in the ionospheric conductances on magnetospheric field‐aligned currents
Authors: Ridley A. J.
Published: February 2007

Through the seasons of the year, the ionospheric potential doesn't change significantly, while the solar driven conductance changes dramatically. This means that the magnetospherically driven field‐aligned currents must be significantly reduced in the winter hemisphere and enhanced in the summer hemisphere. It is shown that, if this simplistic view of the conductance is used, the ratio between the maximum winter FAC and maximum summer hemisphere FAC is on the order of a factor of four. FAC data shows that the true factor is closer to two. When a seasonally dependent auroral precipitation is used to increase the auroral conductance in the winter hemisphere, the ratio between the maximum FAC in the summer and winter is reduced to 1.6. It is shown that the measured hemispheric power does indeed show a seasonal difference, with the winter hemisphere receiving more power by approximately 3.8 GW (about 20%).
Crustal wedging triggering recent deformation in the Andean thrust front between 31°S and 33°S: Sierras Pampeanas‐Precordillera interaction
Authors: Vergés J. , Ramos V. A. , Meigs A. , Cristallini E. , Bettini F. H. , Cortés J. M.
Published: February 2007

We document a new model of crustal structure of the Andean front in Argentina where numerous historic earthquakes destroyed the cities of Mendoza in 1861 (Ms= ∼7) and San Juan in 1944 (Mw= 7.0). The Cerro Salinas anticline is formed above the west directed Cerro Salinas thrust. An east facing monocline with an amplitude of about 2 km folds the Cerro Salinas thrust and overlying Neogene succession. This monocline is formed above a blind crustal thrust in the basement. Its dip of 14° west is inferred from fold geometry. This thick‐skinned east directed blind thrust and the thin‐skinned west directed Cerro Salinas thrust define a tectonic wedge; the wedge tip occurs at a depth of 5.4 km. Growth of the monocline after ∼8.5 Ma is revealed on multichannel seismic (MSC) profile 31017 (Repsol‐YPF). Rates of Cerro Salinas thrust displacement are of the order of 1 mm/yr, whereas vertical uplift of ∼0.45 mm/yr results from the combined displacement on the Cerro Salinas thrust and growth of east facing monocline. The lateral extent of the east directed crustal blind ramp corresponds with the along‐strike extent of the Eastern Precordillera. When combined with the low displacement rate, a long earthquake recurrence interval is implied. Smaller magnitude earthquakes, however, indicate that segments of the blind thrust ramps ruptured in historic events. If all the segments of the blind thrust ruptured together the fault area is ∼7000 km2and could produce aMw∼ 7.7 earthquake. The crustal wedge model provides new constraints on the origin and potential size of earthquakes that threaten the densely populated region.
Cloud properties and associated radiative heating rates in the tropical western Pacific
Authors: Mather James H. , McFarlane Sally A. , Miller Mark A. , Johnson Karen L.
Published: February 2007

Calculations of radiative flux profiles require measurements of thermodynamic and cloud properties (temperature, humidity, liquid and ice water content). Instruments capable of making these measurements have only recently become available. The U.S. Department of Energy Atmospheric Radiation Measurement (ARM) Program operates a comprehensive set of atmospheric remote sensing instruments at sites around the world, including three in the tropical western Pacific region. We have processed several months of ARM observations from two of these sites, Manus and Nauru, to calculate time series of vertical cloud property profiles and associated radiative fluxes and heating rates. Maxima in cloud occurrence are found in the boundary layer and the upper troposphere at both sites. Manus, which was much more convectively active than Nauru during the study period, also exhibits a midlevel cloud feature near the melting level. The two sites exhibit very different diurnal cycles. Manus experiences an afternoon maximum in high clouds while Nauru experiences a weak afternoon minimum. Nauru experiences a strong afternoon maximum in boundary layer clouds. Calculated fluxes at the surface and the top of the atmosphere are found to be in reasonable agreement with measurements. Below 15 km, radiative processes lead to cooling in the average profile, with local maxima near the surface and approximately 8 km. On average, high and midlevel clouds have a net warming effect though not enough to offset the clear‐sky cooling. The prevalent boundary layer clouds at Nauru have a net cooling effect in and above the cloud layer and a net warming below. This data set will be an important tool for describing radiative processes in the tropics and assessing the simulation of these processes in dynamical models.
Identification of Early Markers for Symptomatic Vasospasm in Human Cerebral Microdialysate after Subarachnoid Hemorrhage: Preliminary Results of a Proteome-Wide Screening
Authors: Maurer Martin H , Haux Daniel , Sakowitz Oliver W , Unterberg Andreas W , Kuschinsky Wolfgang
Published: February 2007

A major complication of aneurysmal subarachnoid hemorrhage (SAH) is symptomatic vasospasm, a complex syndrome consisting of neurological deterioration and exclusion of other sources of ischemia. Approximately 30% of SAH patients are affected. Although symptomatic vasospasm is associated with high mortality and poor clinical outcome, it is not possible to identify the individual risk on a molecular level for patients before symptoms have developed. In this study, we hypothesize that protein changes occur in the cerebral microdialysate of patients who later develop symptomatic vasospasm which are not found in matched-pairs control subjects. We searched for changes in protein concentrations in microdialysate sampled from the fronto-temporal brain tissue of five vasospastic and five nonvasospastic SAH patients using proteomics technology based on two-dimensional gel electrophoresis and mass spectrometry. Microdialysate samples were taken at least 1.5 days before the onset of symptomatic vasospasm. Comparing protein expression profiles, we found that the protein concentrations of several isoforms of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) were 1.79-fold ± 1.29 ( N = 5, P < 0.05) higher in the group which later developed symptomatic vasospasm, whereas heat—shock cognate 71 kDa protein (HSP7C) isoforms were decreased to 0.50-fold ± 0.19 ( N = 5, P < 0.05; all expression data means ± s.d.). The changes in protein concentrations were detected 3.8 ± 1.7 days ( N = 5, P < 0.05) before symptomatic vasospasm developed. We conclude that GAPDH and HSP7C may be used as early markers indicating the later development of symptomatic vasospasm after SAH, enabling selective early therapeutic intervention in this high-risk group of patients.
Helicity in the formation of turbulence
Authors: Holm D. D. , Kerr R. M.
Published: February 2007

Helicity in vortex structures and spectra is studied in the developmental stages of a numerical simulation of the Navier-Stokes equations using three-dimensional visualizations and spectra. First, time scales are set using the growth and decay of energy dissipation, the peak value of vorticity, and the helicity. Then, two stages between the early time, nearly inviscid Euler dynamics with vortex sheets and a final state of fully developed turbulence with vortex tubes, are described. In the first stage, helicity fluctuations develop in Fourier space during a period still dominated by vortex sheets and rapidly growing peak vorticity. At the end of this period the strongest structure consists of transverse vortex sheets with mixed signs of helicity. During the second stage, a dissipative interaction propagates along one of these vortices as the sheets roll each other into vortex tubes.
Four-component relativistic theory for nuclear magnetic shielding constants: The orbital decomposition approach
Authors: Xiao Yunlong , Peng Daoling , Liu Wenjian
Published: February 2007

The authors present a scheme to simplify four-component relativistic calculations of nuclear magnetic shielding constants. The central idea is to decompose each first order orbital into two terms, one is magnetically balanced and directly leads to the diamagnetic term, and the other is, to leading order of relativity, kinetically balanced and can therefore simply be represented in the basis of unperturbed positive energy states. As a matrix formulation, the present approach is far simpler than other operator theories. Combined with the Dirac-Kohn-Sham ansatz, the nuclear magnetic shielding constants for the Kr, Xe, and Rn atoms as well as the HBr and HI molecules are calculated, and the results compare favorably with those of other schemes.
Optimization of magnetic properties of electrodeposited CoP multilayers for sensor applications
Authors: Ciudad D. , Prieto J. L. , Lucas I. , Aroca C. , Sánchez P.
Published: February 2007

In this study, we report a method to optimize the coercivity keeping the magnetostriction value constant in electrodeposited CoP multilayers for their applications in magnetoelastic magnetic sensors. We have deposited multilayers of two different compositions of CoP (Co0.74P0.26 and Co0.83P0.17) and studied the influence of the thickness of the different layers, keeping the total thickness constant. The results show a saturation magnetostriction in between the values of the magnetostriction of the two materials and independent of the thickness of the layers. However, the reduction of the thickness of the layers is accompanied with a clear reduction of the coercive field to values as low as 0.5Oe and with a large increase of the permeability. This result shows, in the same material, an appreciable value of magnetostriction combined with low coercivity. Additionally we have found a controllable influence of the hydrogen flow on the direction of anisotropy which, in combination with other results, allows us to customize the material for its application in magnetic sensors.
Dynamic spreading of a liquid finger driven by electrowetting: Theory and experimental validation
Authors: Tanguy Laurent , Leïchlé Thierry , Nicu Liviu
Published: February 2007

Electrowetting on dielectrics is now a major field of research for lab-on-chip applications. Droplets and liquid fingers are used to displace, mix, and analyze biological compounds. The creation and propagation of a liquid finger are investigated here for a channel with an elliptical cross section. Forces acting on the liquid are described and calculated, and the problem is solved using a steady-state equation. The theoretical length of the finger as a function of time is expressed and the threshold voltage for finger formation is deduced. Test devices fabricated in highly doped silicon are used to validate our theory. Liquid fingers propagating into the fabricated microchannels are extracted from microliter droplets using 1kHz ac voltages ranging from 80to180Vrms. The resulting experimental threshold voltages and the dynamic lengths are compared to the theoretical predictions. Additional discussions and calculations are proposed to improve our model so that the experimental conditions are more accurately described.
Emission mechanism in organic light-emitting devices comprising a europium complex as emitter and an electron transporting material as host
Authors: Xin Q. , Li W. L. , Su W. M. , Li T. L. , Su Z. S. , Chu B. , Li B.
Published: February 2007

The emission mechanism in organic light-emitting devices, where the emission layer is composed of Eu(DBM)3pyzphen (DBM=Dibenzoylmethane, pyzphen=pyrazino-[2,3-f][1,10]-phenanthroline) doped into electron transporting/hole blocking material BPhen (4,7-diphenyl-1, 10-phenanthroline), is investigated. Energy transfer and carrier trapping simultaneously exist in the luminescence process, and carrier trapping is a main process. Direct carrier trapping by Eu(DBM)3pyzphen molecules is confirmed by the difference of electroluminescence and photoluminescence spectra as well as J-V characteristics. Efficient Föster and Dexter energy transfer from BPhen to Eu(DBM)3pyzphen molecules were speculated in terms of analysis of photoluminescence spectra of fixed solutions, triplet energies, and phosphorescent lifetimes. Based on these mechanisms, the overall performances of these devices were improved. High efficiencies were obtained under carrier trapping by Eu(DBM)3pyzphen molecules, and the emission of BPhen was eliminated by efficient energy transfer from the BPhen to Eu(DBM)3pyzphen molecules.
Mobile spectroscopic system for trace gas detection using a tunable mid-IR laser
Authors: Vaičikauskas V. , Kaučikas M. , Švedas V. , Kuprionis Z.
Published: February 2007

We describe a mobile spectroscopic system for trace gas analysis based on the open path differential absorption spectrometer and the photoacoustic spectrometer. The first method allows long distance measurements (up to a few kilometers) while the second one provides local in situ detection of pollutants. The open path system is based on the nanosecond (f=10Hz, τ≈5ns) lamp pumped Nd:YAG laser and a tunable two cascade optical parametric generator operating in the 5–12μm spectral region. This source was mounted into the lidar setup based on the coaxial transmitter/receiver. The photoacoustic system was constructed using the same laser as well as a nonresonant photoacoustic cell.
Determining the absolute efficiency of a delay line microchannel-plate detector using molecular dissociation
Authors: Gaire B. , Sayler A. M. , Wang P. Q. , Johnson Nora G. , Leonard M. , Parke E. , Carnes K. D. , Ben-Itzhak I.
Published: February 2007

We present a method to measure the absolute detection efficiency of a delay-line microchannel-plate detector using the breakup of diatomic molecular ions. This method provides the absolute total detection efficiency, as well as the individual efficiency for each signal of the detector. The method is based on the fact that molecular breakup always yields two hits on the detector, but due to finite detection efficiency some of these events are recorded as single particles while others are detected in pairs. We demonstrate the method by evaluating the detection efficiency for both timing and position signals of a delay-line detector using laser-induced dissociation of molecular ions. In addition, the detection efficiency as a function of position has been determined by dividing the detector into sectors.
Numerical simulations of granular materials flow around obstacles: The role of the interstitial gas
Authors: Levy Avi , Sayed Mohamed
Published: February 2007

A two-fluid model was used to determine the influence of the gas phase on granular flow interaction with obstacles. The governing equations of two-dimensional, two-phase flow were solved numerically using a finite-volume-based numerical code. The numerical results are qualitatively compared to experimental observations from various sources, and good agreement is found. Several cases were tested in order to examine the role of the velocities of both phases, solid volume fraction, particle diameter, and gravity. The results show that under certain conditions, particularly for dilute flows, a bow granular shock wave clearly forms in the front of the obstacle. Alternatively, for dense flows, granular shock waves were not observed. Based on the present observations, it appears that the formation and the shape of the bow granular shock wave are influenced by the interaction between the solid and gas phases and the gravity force. The results indicate that the common assumptions of neglecting both the gravity and the influence of the gas phase on the granular flow, may be appropriate only in the vicinity of the obstacle, where granular creeping flow takes place.
Temperature effects on the spectral properties of colloidal CdSe nanodots, nanorods, and tetrapods
Authors: Al Salman A. , Tortschanoff A. , Mohamed M. B. , Tonti D. , van Mourik F. , Chergui M.
Published: February 2007

The temperature dependence of the absorption and fluorescence spectra of colloidal CdSe nanocrystals was compared for three different shapes (dots, rods, and tetrapods) in the range of 4–300K. While the shift of the fluorescence maximum indicates little dependence on the shape, the authors find that the broadening of the emission spectrum behaves very differently for dots and rods, indicating major differences in the broadening mechanisms for different shapes. Tetrapods behave more similarly to dots, which suggests that the lowest exciton state is centered at the core.
Interacting systems for self-correcting low power switching
Authors: Salahuddin Sayeef , Datta Supriyo
Published: February 2007

This letter first shows that dynamic switching schemes can be used to reduce energy dissipation below the thermodynamic minimum of NkTlnr (N=number of information carriers and 1∕r=error probability), but only at the expense of the error immunity inherent in thermodynamic processes for which the final state is insensitive to the switching dynamics. It is further shown that, for a system which has internal feedback, e.g., nanomagnets, such that all N spins act in concert, it should be possible to switch with an energy dissipation of the order of kTlnr (considerably less than the thermodynamic limit of NkTlnr), while retaining an error immunity comparable to thermodynamic switching.
Spin injection into a single self-assembled quantum dot in a p-i-n II-VI/III-V structure
Authors: Ghali M. , Arians R. , Kümmell T. , Bacher G. , Wenisch J. , Mahapatra S. , Brunner K.
Published: February 2007

The authors report on efficient spin injection from a n-Zn0.96Mn0.04Se layer into an InAs single quantum dot (SQD) in a p-i-n diode structure using magnetomicrophotoluminescence experiments. A circular polarization degree of up to 60% at B=5T is obtained from the InAs single dot emission while no polarized light is observed in a structure with no electrical doping of any of its layers. A pronounced dependence of the spin injection efficiency on the external bias is found resulting in a strong decrease of the SQD circular polarization degree when the biasing is applied in the forward direction. The experiments emphasize the impact of excess energy and current flow on the spin injection efficiency in a SQD.
Ballistic electron transport through titanylphthalocyanine films
Authors: Özcan S. , Smoliner J. , Andrews M. , Strasser G. , Dienel T. , Franke R. , Fritz T.
Published: February 2007

In this letter, Au/tanylphthalocyanine/GaAs diodes incorporating ultrathin films of the archetypal organic semiconductor titanylphthalocyanine were investigated by ballistic electron emission microscopy (BEEM)/spectroscopy. The presence of the organic semiconductor increases the BEEM threshold voltage compared to reference Au∕GaAs diodes. The Schottky barrier heights were measured for various temperatures and show an approximately linear increase from 1.2eV at room temperature to 1.5eV at T=10K.
Vortex shedding from a circular cylinder near a moving ground
Authors: Nishino Takafumi , Roberts Graham T. , Zhang Xin
Published: February 2007

The flow and force characteristics have been experimentally investigated of a circular cylinder with an aspect ratio of 8.33, with and without end-plates, placed near and parallel to a moving ground, on which substantially no boundary layer developed to interfere with the cylinder. Mean drag and lift measurements, surface oil flow visualization, and particle image velocimetry (PIV) measurements were carried out at two upper-subcritical Reynolds numbers of 0.4 and 1.0×105 (based on the cylinder diameter d) to investigate the mechanisms of the ground effect, i.e., the effect of the gap-to-diameter ratio h∕d, where h is the gap between the cylinder and the ground. For the cylinder with end-plates, on which the oil flow patterns were observed to be essentially two-dimensional, the drag rapidly decreased as h∕d decreased to less than 0.5 but became constant for h∕d of less than 0.35, unlike that usually observed near a fixed ground. This critical drag behavior was found to be directly related to a global change in the near wake structure of the cylinder; as h∕d decreased the Kármán-type vortex shedding became intermittent at h∕d=0.4, and then totally ceased and instead two nearly parallel shear layers were formed behind the cylinder at h∕d=0.3 and below. For the cylinder without end-plates, however, no such critical change in drag was observed as the Kármán-type vortices were not generated in the near wake region at all h∕d investigated. Based on the experimental results obtained, further discussions are also given to the essential cause of the cessation of the Kármán vortex shedding in the ground effect.
Formation of polybromine anions and concurrent heavy hole doping in carbon nanotubes
Authors: Sung Dongchul , Park Noejung , Park Wanjun , Hong Suklyun
Published: February 2007

Using density-functional theory calculations, we investigate the atomic and electronic structure of the bromine species encapsulated in carbon nanotubes. We find that the odd-membered molecular structures (Br3 and Br5) are energetically favored than the common Br2 molecule. The transformation from bromine molecules (Br2) into Br3 or Br5 is found to be almost barrierless. A strong electron transfer from the nanotube to the adsorbates, which has been doubtful in previous studies, is accompanied by the formation of such odd-membered polybromine anions. We suggest that the tip-opened carbon nanotube samples can be heavily hole-doped after exposure to Br2 gas.
DgrA is a member of a new family of cyclic diguanosine monophosphate receptors and controls flagellar motor function in
Caulobacter crescentus
Authors: Christen Matthias , Christen Beat , Allan Martin G. , Folcher Marc , Jenö Paul , Grzesiek Stephan , Jenal Urs
Published: February 2007

Bacteria are able to switch between two mutually exclusive lifestyles, motile single cells and sedentary multicellular communities that colonize surfaces. These behavioral changes contribute to an increased fitness in structured environments and are controlled by the ubiquitous bacterial second messenger cyclic diguanosine monophosphate (c-di-GMP). In response to changing environments, fluctuating levels of c-di-GMP inversely regulate cell motility and cell surface adhesins. Although the synthesis and breakdown of c-di-GMP has been studied in detail, little is known about the downstream effector mechanisms. Using affinity chromatography, we have isolated several c-di-GMP-binding proteins from
Caulobacter crescentus
. One of these proteins, DgrA, is a PilZ homolog involved in mediating c-di-GMP-dependent control of
C. crescentus
cell motility. Biochemical and structural analysis of DgrA and homologs from
C. crescentus
,
Salmonella typhimurium
, and
Pseudomonas aeruginosa
demonstrated that this protein family represents a class of specific diguanylate receptors and suggested a general mechanism for c-di-GMP binding and signal transduction. Increased concentrations of c-di-GMP or DgrA blocked motility in
C. crescentus
by interfering with motor function rather than flagellar assembly. We present preliminary evidence implicating the flagellar motor protein FliL in DgrA-dependent cell motility control.
Regulation of Alzheimer's disease amyloid-β formation by casein kinase I
Authors: Flajolet Marc , He Gen , Heiman Myriam , Lin Angie , Nairn Angus C. , Greengard Paul
Published: February 2007

Alzheimer's disease (AD) is associated with accumulation of the neurotoxic peptide amyloid-β (Aβ), which is produced by sequential cleavage of amyloid precursor protein (APP) by the aspartyl protease β-secretase and the presenilin-dependent protease γ-secretase. An increase of casein kinase 1 (CK1) expression has been described in the human AD brain. We show, by using
in silico
analysis, that APP, β-secretase, and γ-secretase subunits contain, in their intracellular regions, multiple CK1 consensus phosphorylation sites, many of which are conserved among human, rat, and mouse species. Overexpression of constitutively active CK1ε, one of the CK1 isoforms expressed in brain, leads to an increase in Aβ peptide production. Conversely, three structurally dissimilar CK1-specific inhibitors significantly reduced endogenous Aβ peptide production. By using mammalian cells expressing the β C-terminal fragment of APP, it was possible to demonstrate that CK1 inhibitors act at the level of γ-secretase cleavage. Importantly, Notch cleavage was not affected. Our results indicate that CK1 represents a therapeutic target for prevention of Aβ formation in AD.
Separation of receptor-binding and profusogenic domains of glycoprotein D of herpes simplex virus 1 into distinct interacting proteins
Authors: Zhou Guoying , Roizman Bernard
Published: February 2007

The 369-residue glycoprotein D (gD) is the entry, receptor-binding protein of herpes simplex virus 1. The common receptors for viral entry are nectin-1, HveA, and a specific O-linked sulfated proteoglycan. The major receptor-binding sites of gD are at the N terminus, whereas the domain required for fusion of viral envelope with the plasma membrane is at the C terminus of the ectodomain (residues 260–310). In the course of retargeting gD to the urokinase plasminogen activator (uPA) receptor for potential therapeutic applications, we obtained a genetically engineered infectious virus in which the receptor-binding domain consisting of the N-terminal domain of uPA fused to residues 33–60 of gD was separated from an independently expressed C-terminal domain of gD containing residues 219–369. The intervening sequences (residues 62–218) were replaced by a stop codon and a promoter for the C-terminal domain of gD. The physical interaction of the two components was reconstructed by coimmunoprecipitation of the N-terminal domain of uPA with the C-terminal domain of gD. These results indicate that codons 61–218 of gD do not encode executable functions required for viral entry into cells and suggest that the receptor-binding ligand must interact with but need not alter the structure of the residual portion of gD to effect virus entry. This finding opens the way for the development of a family of recombinant viruses in which the profusion domain of gD and independently furnished, interacting receptor-binding domains effect entry of the virus via a range of receptors.
Urocortin 3 regulates glucose-stimulated insulin secretion and energy homeostasis
Authors: Li Chien , Chen Peilin , Vaughan Joan , Lee Kuo-Fen , Vale Wylie
Published: February 2007

Urocortin 3 (Ucn 3), a member of the corticotropin-releasing factor (CRF) family of peptides, is strongly expressed in mammalian pancreatic β cells and has been shown to stimulate insulin secretion. Here we report the investigation of the hypothesis that endogenous Ucn 3 regulates insulin secretion, particularly in the presence of nutrient excess. Secretion of Ucn 3-like immunoreactivity from cultured β cells was stimulated by high glucose and insulin secretagogs such as GLP-1; furthermore, 5 pancreatic Ucn 3 mRNA levels
in vivo
were increased during the positive energy balance caused by high-fat diet and by the absence of leptin. Immunoneutralization of Ucn 3 or pharmacologic blockade of its receptor, the type 2 CRF receptor (CRFR2), attenuated high but not low glucose-induced insulin secretion from isolated islets
in vitro
. Cultured islets isolated from Ucn 3-null mice also secreted less insulin in response to high glucose concentrations. Consistently, peripheral injection of a selective CRFR2 antagonist before the administration of a glucose challenge significantly attenuated glucose-induced insulin secretion
in vivo
. Ucn 3-null mice were relatively protected from the hyperinsulinemia, hyperglycemia, glucose intolerance, hepatic steatosis, and hypertriglyceridemia induced by high-fat diet. Additionally, we found that aged Ucn 3-null mice maintained better glucose tolerance than age-matched wild-type littermates. These results suggest that endogenous Ucn 3 in the pancreas is induced under excessive caloric conditions and acts locally to augment insulin production, which in the long-term may contribute to reduced insulin sensitivity and harmful metabolic consequences.
Hedgehog signaling maintains a tumor stem cell compartment in multiple myeloma
Authors: Peacock Craig D. , Wang Qiuju , Gesell Gregory S. , Corcoran-Schwartz Ian M. , Jones Evan , Kim Jynho , Devereux Wendy L. , Rhodes Jonathan T. , Huff Carol A. , Beachy Philip A. , Watkins D. Neil , Matsui William
Published: February 2007

The cancer stem cell hypothesis suggests that malignant growth depends on a subset of tumor cells with stem cell-like properties of self-renewal. Because hedgehog (Hh) signaling regulates progenitor cell fate in normal development and homeostasis, aberrant pathway activation might be involved in the maintenance of such a population in cancer. Indeed, mutational activation of the Hh pathway is associated with medulloblastoma and basal cell carcinoma; pathway activity is also critical for growth of other tumors lacking such mutations, although the mechanism of pathway activation is poorly understood. Here we study the role and mechanism of Hh pathway activation in multiple myeloma (MM), a malignancy with a well defined stem cell compartment. In this model, rare malignant progenitors capable of clonal expansion resemble B cells, whereas the much larger tumor cell population manifests a differentiated plasma cell phenotype that pathologically defines the disease. We show that the subset of MM cells that manifests Hh pathway activity is markedly concentrated within the tumor stem cell compartment. The Hh ligand promotes expansion of MM stem cells without differentiation, whereas the Hh pathway blockade, while having little or no effect on malignant plasma cell growth, markedly inhibits clonal expansion accompanied by terminal differentiation of purified MM stem cells. These data reveal that Hh pathway activation is heterogeneous across the spectrum of MM tumor stem cells and their more differentiated progeny. The potential existence of similar relationships in other adult cancers may have important biologic and clinical implications for the study of aberrant Hh signaling.
Cortical area size dictates performance at modality-specific behaviors
Authors: Leingärtner Axel , Thuret Sandrine , Kroll Todd T. , Chou Shen-Ju , Leasure J. Leigh , Gage Fred H. , O'Leary Dennis D. M.
Published: February 2007

The mammalian neocortex is organized into unique areas that serve functions such as sensory perception and modality-specific behaviors. The sizes of primary cortical areas vary across species, and also within a species, raising the question of whether area size dictates behavioral performance. We show that adult mice genetically engineered to overexpress the transcription factor EMX2 in embryonic cortical progenitor cells, resulting in reductions in sizes of somatosensory and motor areas, exhibit significant deficiencies at tactile and motor behaviors. Even increasing the size of sensorimotor areas by decreasing cortical EMX2 levels can lead to diminished sensorimotor behaviors. Genetic crosses that retain ectopic
Emx2
transgene expression subcortically but restore cortical
Emx2
expression to wild-type levels also restore cortical areas to wild-type sizes and in parallel restore tactile and motor behaviors to wild-type performance. These findings show that area size can dictate performance at modality-specific behaviors and suggest that areas have an optimal size, influenced by parameters of its neural system, for maximum behavioral performance. This study underscores the importance of establishing during embryonic development appropriate levels of regulatory proteins that determine area sizes, thereby influencing behavior later in life.
Restriction of endogenous T cell antigen receptor β rearrangements to Vβ14 through selective recombination signal sequence modifications
Authors: Wu Cherry , Ranganath Sheila , Gleason Megan , Woodman Barbara B. , Borjeson Tiffany M. , Alt Frederick W. , Bassing Craig H.
Published: February 2007

T cell antigen receptor (TCR)β V(D)J variable region exon assembly is ordered, with Dβ to Jβ rearrangements occurring before joining of Vβs to a DJβ complex. Germ-line V(D)J segments are flanked by recombination signal (RS) sequences, which consist of heptamers and nonamers separated by a spacer of 12 (12-RS) or 23 (23-RS) bp. V(D)J recombination is restricted by the 12/23 rule; joining occurs only between gene segments flanked by 12-RSs and 23-RSs. Vβ segments have 23-RSs and Jβ segments 12-RSs, which based on the 12/23 rule should allow direct joining. However, Vβ segments rearrange only to DJβ complexes and not Jβ segments, because of restrictions beyond 12/23 (B12/23) that make the Vβ23-RS incompatible with the Jβ12-RS. To determine whether direct Vβ to Jβ joining occurs if flanking RSs are B12/23 compatible, we generated mice whose lymphocytes contained replacement of the Vβ1412-RS with the 3′Dβ112-RS on a TCRβ allele lacking Dβ segments (the Jβ1M6allele). Mice heterozygous for the Jβ1M6allele had dramatically increased Vβ14+thymocyte and T cell numbers and decreased numbers of cells expressing other Vβs. This altered Vβ repertoire resulted from direct Vβ14 to Jβ1 rearrangements on the Jβ1M6allele. Mice harboring lymphocytes homozygous for Jβ1M6allele developed normal thymocyte and T cell numbers with all expressing Vβ14. Our findings show that selective RS modifications enforce rearrangement of a specific Vβ gene segment and demonstrate the importance of B12/23 mechanisms for ensuring generation of diverse TCRβ repertoires.
Induction of the
celC
operon of
Clostridium thermocellum
by laminaribiose
Authors: Newcomb Michael , Chen Chun-Yu , Wu J. H. David
Published: February 2007

Clostridium thermocellum
is an anaerobic, thermophilic, cellulolytic, and ethanogenic bacterium. It produces an extracellular multiprotein complex termed the cellulosome, which consists of >70 subunits, most of them glycosyl hydrolases. It also produces many free glycosyl hydrolases. How the organism commands such a large number of genes and proteins for biomass degradation is an intriguing yet unresolved question. We identified
glyR3
, which is cotranscribed with the cellulase/hemicellulase genes
celC
and
licA
, as a potential cellulase transcription regulator. The gel-shift assay (EMSA) revealed that the recombinant GlyR3 bound specifically to the
celC
promoter region. GlyR3 was also identified from the lysate of the lichenan-grown cells, which bound to the same sequence. DNase I footprinting and competitive EMSA showed the binding site to be an 18-bp palindromic sequence with one mismatch. The DNA-binding activity was specifically inhibited by laminaribiose, a β-1-3 linked glucose dimer, in a dose-dependent manner. In
in vitro
transcription analysis,
celC
expression was repressed by rGlyR3 in a dose-dependent manner. The repression was relieved by laminaribiose, also in a dose-dependent manner. These results indicate that GlyR3 is a negative regulator of the
celC
operon consisting of
celC
,
glyR3
, and
licA
, and inducible by laminaribiose. Thus, the bacterium may modulate the biosynthesis of its enzyme components to optimize its activity on an available biomass substrate, in this case, β-1-3 glucan, because both CelC and LicA are active on the substrate. The results further indicate that, despite the insolubility of the biomass substrate, regulation of the degradative enzymes can be accomplished through soluble sugars generated by the action of the enzymes.
Ink4a
/
Arf
tumor suppressor does not modulate the degenerative conditions or tumor spectrum of the telomerase-deficient mouse
Authors: Khoo Christine M. , Carrasco Daniel R. , Bosenberg Marcus W. , Paik Ji-Hye , DePinho Ronald A.
Published: February 2007

The Rb/p16
Ink4a
and p53/p19Arf tumor suppressor pathways have been linked to diverse cancer-relevant processes, including those governing the cellular responses to telomere dysfunction. In this study, we sought to provide direct genetic evidence of a role for the Ink4a/Arf tumor suppressor gene, encoding both p16
Ink4a
and p19
Arf
, in modulating the cellular and tissue phenotypes associated with telomere dysfunction by using the
mTerc Ink4a/Arf
mouse model. In contrast to the rescue associated with p53 deficiency, Ink4a/Arf deficiency did not attenuate the degenerative phenotypes elicited by telomere dysfunction in the late-generation
mTerc
−/− mice. Furthermore, in contrast to accelerated cancer onset and increased epithelial cancers of late-generation
mTerc
−/−
p53
mutant mice, late-generation
mTerc
−/−
Ink4a/Arf
mutant mice experienced a delayed tumor onset and maintained the lymphoma and sarcoma spectrum. Consistent with the negligible role of Ink4a/Arf in the telomere checkpoint response
in vivo
, late-generation
mTerc
−/−
Ink4a/Arf
−/− tissues show activated p53, and derivative tumor cell lines sustain frequent loss of p53 function, whereas all early generation
mTerc Ink4a/Arf
−/− tumor cell lines remain intact for p53. In addition, the late-generation
mTerc
−/−
Ink4a/Arf
−/− tumors showed activation of the alternative lengthening of telomere mechanism, underscoring the need for adaptation to the presence of telomere dysfunction in the absence of p16
Ink4a
and p19
Arf
. These observations highlight the importance of genetic context in dictating whether telomere dysfunction promotes or suppresses age-related degenerative conditions as well as the rate of initiation and type of spontaneous cancers.
PostoperativeChryseobacterium indologenesBloodstream Infection Caused by Contamination of Distillate Water
Authors: Bayraktar Mehmet Refik , Aktas Elif , Ersoy Yasemin , Cicek Aysegul , Durmaz Riza
Published: February 2007

Chryseobacterium indologeneswas isolated from blood samples from a 5-month-old infant with bloodstream infection. Environmental sampling was performed. Molecular typing with arbitrarily primed polymerase chain reaction demonstrated the cross-contamination of commercial distillate water. The infant was infected by this water as a result of medical assistance received during hospitalization.
Hand Hygiene Practices After Brief Encounters With Patients: An Important Opportunity for Prevention
Authors: Dedrick Rebecca E. , Sinkowitz-Cochran Ronda L. , Cunningham Candace , Muder Robert R. , Perreiah Peter , Cardo Denise M. , Jernigan John A.
Published: February 2007

Objective.

To identify characteristics of encounters between healthcare workers (HCWs) and patients that correlated with hand hygiene adherence among HCWs.

Design.

Observational study.

Setting.

Intensive care unit in a Veterans Affairs hospital.

Participants.

HCWs.

Results.

There were 767 patient encounters observed (48.6% involved nurses, 20.6% involved physicians, and 30.8% involved other HCWs); 39.8% of encounters involved patients placed under contact precautions. HCW contact with either the patient or surfaces in the patient's environment occurred during all encounters; direct patient contact occurred during 439 encounters (57.4%), and contact with environmental surfaces occurred during 710 encounters (92.6%). The median duration of encounters was 2 minutes (range, <1 to 51 minutes); 33.6% of encounters lasted 1 minute or less, with no significant occupation-associated differences in the median duration of encounters. Adherence with hand hygiene practices was correlated with the duration of the encounter, with overall adherences of 30.0% after encounters of ≤1 minute, 43.4% after encounters of >1 to ≤2 minutes, 51.1% after encounters of >3 to ≤5 minutes, and 64.9% after encounters of >5 minutes (P < .001 by the x2 for trend). In multivariate analyses, longer encounter duration, contact precautions status, patient contact, and nursing occupation were independently associated with adherence to hand hygiene recommendations.

Conclusions.

In this study, adherence to hand hygiene practices was lowest after brief patient encounters (ie, <2 minutes). Brief encounters accounted for a substantial proportion of all observed encounters, and opportunities for hand contamination occurred during all brief encounters. Therefore, improving adherence after brief encounters may have an important overall impact on the transmission of healthcare-associated pathogens and may deserve special emphasis in the design of programs to promote adherence to hand hygiene practices.
Assessment of Healthcare Professionals' Adherence to Hand Hygiene After Alcohol-Based Hand Rub Introduction at an Intensive Care Unit in São Paulo, Brazil
Authors: Santana Solange L. , Furtado Guilherme H. C. , Coutinho Ana Paula , Medeiros Eduardo A. S.
Published: February 2007

We analyzed the impact of introducing an alcohol-based hand gel and an educational program on hand hygiene adherence among healthcare workers in an intensive care unit. Adherence to hand hygiene was significantly higher after the intervention for the night shift work period (P = .001), among nursing assistants (P = .001), among nurses (P = .007) on weekend days (P = .016), and for invasive procedures (P = .012).