bluuebunny/crossref_metadata_2025_split huggingface dataset:
Is there a role for T-type Ca2+channels in regulation of vasomotor tone in mesenteric arterioles?This article is part of a Special Issue on Information Transfer in the Microcirculation.
Authors: Jensen Lars Jørn , Holstein-Rathlou Niels-Henrik 
Published: January 2009

The largest peripheral blood pressure drop occurs in terminal arterioles (<40 µm lumen diameter). L-type voltage-dependent Ca2+channels (VDCCs) are considered the primary pathway for Ca2+influx during physiologic activation of vascular smooth muscle cells (VSMC). Recent evidence suggests that T-type VDCCs are expressed in renal afferent and efferent arterioles, mesenteric arterioles, and skeletal muscle arterioles. T-type channels are small-conductance, low voltage-activated, fast-inactivating channels. Thus, their role in supplying Ca2+for contraction of VSMC has been disputed. However, T-type channels display non-inactivating window currents, which may play a role in sustained Ca2+entry. Here, we review the possible role of T-type channels in vasomotor tone regulation in rat mesenteric terminal arterioles. The CaV3.1 channel was immunolocalized in VSMC, whereas the CaV3.2 channel was predominantly expressed in endothelial cells. Voltage-dependent Ca2+entry was inhibited by the new specific T-type blockers R(–)-efonidipine and NNC 55-0396. The effect of NNC 55-0396 persisted in depolarized arterioles, suggesting an unusually high activation threshold of mesenteric T-type channels. T-type channels were not necessary for conduction of vasoconstriction, but appear to be important for local electromechanical coupling in VSMC. The first direct demonstration of endothelial T-type channels warrants new investigations of their role in vascular biology.
Role of spleen in integrated control of splanchnic vascular tone: physiology and pathophysiologyThis article is part of a Special Issue on Information Transfer in the Microcirculation.
Authors: Hamza Shereen M. , Kaufman Susan 
Published: January 2009

Aside from its established immunologic and hematologic functions, the spleen also plays an important role in cardiovascular regulation. This occurs through changes in intrasplenic microvascular tone, as well as through splenic neurohormonal modulation of the renal and mesenteric vascular beds. Splenic regulation of blood volume occurs predominantly through fluid extravasation from the splenic circulation into lymphatic reservoirs; this is controlled by direct modulation of splenic pre- and postcapillary resistance by established physiologic agents such as atrial natriuretic peptide (ANP), nitric oxide (NO), and adrenomedullin (ADM). In addition to physiologic fluid regulation, splenic extravasation is a key factor in the inability to maintain adequate intravascular volume in septic shock. The spleen also controls renal microvascular tone through reflex activation of the splenic afferent and renal sympathetic nerves. This splenorenal reflex not only contributes to the physiologic regulation of blood pressure, but also contributes to the cardiovascular dysregulation associated with both septic shock and portal hypertension. In septic shock, the splenorenal reflex protectively limits splenic extravasation and potentially promotes renal sodium and water reabsorption and release of the vasoconstrictor angiotensin II; this function is eventually overwhelmed as shock progresses. In portal hypertension, on the other hand, the splenorenal reflex-mediated reduction in renal vascular conductance exacerbates sodium and water retention in the kidneys and may eventually contribute to renal dysfunction. Preliminary evidence suggests that the spleen also may play a role in the hemodynamic complications of portal hypertension via neurohormonal modulation of the mesenteric vascular bed. Lastly, the spleen itself may be a source of a vasoactive factor.
Special-Purpose Hardware for Solving the Elliptic Curve Discrete Logarithm Problem
Authors: Güneysu Tim , Paar Christof , Pelzl Jan 
Published: January 2009

The resistance against powerful index-calculus attacks makes Elliptic Curve Cryptosystems (ECC) an interesting alternative to conventional asymmetric cryptosystems, like RSA. Operands in ECC require significantly less bits at the same level of security, resulting in a higher computational efficiency compared to RSA. With growing computational capabilities and continuous technological improvements over the years, however, the question of the security of ECC against attacks based on special-purpose hardware arises. In this context, recently emerged low-cost FPGAs demand for attention in the domain of hardware-based cryptanalysis: the extraordinary efficiency of modern programmable hardware devices allow for a low-budget implementation of hardware-based ECC attacks---without the requirement of the expensive development of ASICs.
With focus on the aspect of cost-efficiency, this contribution presents and analyzes an FPGA-based architecture of an attack against ECC over prime fields. A multi-processing hardware architecture for Pollard's Rho method is described. We provide results on actually used key lengths of ECC (128 bits and above) and estimate the expected runtime for a successful attack.
As a first result, currently used elliptic curve cryptosystems with a security of 160 bit and above turn out to be infeasible to break with available computational and financial resources. However, some of the security standards proposed by the Standards for Efficient Cryptography Group (SECG) become subject to attacks based on low-cost FPGAs.
On the trade-off between power and flexibility of FPGA clock networks
Authors: Lamoureux Julien , Wilton Steven J. E. 
Published: January 2009

FPGA clock networks consume a significant amount of power, since they toggle every clock cycle and must be flexible enough to implement the clocks for a wide range of different applications. The efficiency of FPGA clock networks can be improved by reducing this flexibility; however, reducing the flexibility introduces stricter constraints during the clustering and placement stages of the FPGA CAD flow. These constraints can reduce the overall efficiency of the final implementation. This article examines the trade-off between the power consumption and flexibility of FPGA clock networks.
Specifically, this article makes three contributions. First, it presents a new parameterized clock-network framework for describing and comparing FPGA clock networks. Second, it describes new clock-aware placement techniques that are needed to find a legal placement satisfying the constraints imposed by the clock network. Finally, it performs an empirical study to examine the trade-off between the power consumption of the clock network and the impact of the CAD constraints for a number of different clock networks with varying amounts of flexibility.
The results show that the techniques used to produce a legal placement can have a significant influence on power and the ability of the placer to find a legal solution. On average, circuits placed using the most effective techniques dissipate 5% less overall energy and are significantly more likely to be legal than circuits placed using other techniques. Moreover, the results show that the architecture of the clock network is also important. On average, FPGAs with an efficient clock network are up to 14.6% more energy efficient compared to other FPGAs.
Genesis of Tropical Storm Eugene (2005) from Merging Vortices Associated with ITCZ Breakdowns. Part II: Roles of Vortex Merger and Ambient Potential Vorticity
Authors: Kieu Chanh Q. , Zhang Da-Lin 
Published: January 2009

Abstract
In this study, the roles of merging midlevel mesoscale convective vortices (MCVs) and convectively generated potential vorticity (PV) patches embedded in the intertropical convergence zone (ITCZ) in determining tropical cyclogenesis are examined by calculating PV and absolute vorticity budgets with a cloud-resolving simulation of Tropical Storm Eugene (2005). Results show that the vortex merger occurs as the gradual capture of small-scale PV patches within a slow-drifting MCV by another fast-moving MCV, thus concentrating high PV near the merger’s circulation center, with its peak amplitude located slightly above the melting level. The merging phase is characterized by sharp increases in surface heat fluxes, low-level convergence, latent heat release (and upward motion), lower tropospheric PV, surface pressure falls, and growth of cyclonic vorticity from the bottom upward. Melting and freezing appear to affect markedly the vertical structures of diabatic heating, convergence, absolute vorticity, and PV, as well the production of PV during the life cycle of Eugene. Results also show significant contributions of the horizontal vorticity to the magnitude of PV and its production within the storm.
The storm-scale PV budgets show that the above-mentioned amplification of PV results partly from the net internal dynamical forcing between the PV condensing and diabatic production and partly from the continuous lateral PV fluxes from the ITCZ. Without the latter, Eugene would likely be shorter lived after the merger under the influence of intense vertical shear and colder sea surface temperatures. The vorticity budget reveals that the storm-scale rotational growth occurs in the deep troposphere as a result of the increased flux convergence of absolute vorticity during the merging phase. Unlike the previously hypothesized downward growth associated with merging MCVs, the most rapid growth rate is found in the bottom layers of the merger because of the frictional convergence. It is concluded that tropical cyclogenesis from merging MCVs occurs from the bottom upward.
Atlantic Subtropical Storms. Part II: Climatology
Authors: Guishard Mark P. , Evans Jenni L. , Hart Robert E. 
Published: January 2009

Abstract
A 45-yr climatology of subtropical cyclones (ST) for the North Atlantic is presented and analyzed. The STs pose a warm-season forecasting problem for subtropical locations such as Bermuda and the southern United States because of the potentially rapid onset of gale-force winds close to land. Criteria for identification of ST have been developed based on an accompanying case-study analysis. These criteria are applied here to the 40-yr European Centre for Medium-Range Weather Forecasts Re-Analysis (ERA-40) to construct a consistent historical database of 197 North Atlantic ST in 45 yr.
Because ST may eventually evolve into tropical cyclones, sea surface temperatures (SST) and vertical wind shear conditions for tropical cyclogenesis are contrasted with the conditions for ST genesis identified here. Around 60% of the 197 ST formed over SST in excess of 25°C in a region of weak static stability. Further, the mean environmental vertical wind shear at formation for these storms is 10.7 m s−1, a magnitude generally considered to be unfavorable for tropical cyclogenesis.
The STs have hybrid structure, so the potential for baroclinic and thermodynamic development is explored through the baroclinic zone (characterized by the Eady growth rate σ) and SST field. Seasonal evolution in the location and frequency of ST formation in the basin is demonstrated to correspond well to the changing region of overlap between SST &gt; 25°C and σ &gt; 0.1 day−1.
This climatology is contrasted with two alternative ST datasets. The STs contribute to 12% of tropical cyclones (TC) in the current National Hurricane Center (NHC) Hurricane Database (HURDAT); this equivalent to about 1 in 8 genesis events from an incipient ST disturbance. However, with the addition of 144 ST that are newly identified in this climatology (and not presently in HURDAT) and the reclassification (as not ST) of 65 existing storms in HURDAT, 197/597 storms (33%) in the newly combined database are ST, which emphasizes the potential importance of these warm-season storms.
Linking the Pacific Meridional Mode to ENSO: Coupled Model Analysis
Authors: Zhang Li , Chang Ping , Ji Link 
Published: January 2009

Abstract
The occurrence of a boreal spring phenomenon referred to as the Pacific meridional model (MM) is shown to be intimately linked to the development of El Niño–Southern Oscillation (ENSO) in a long simulation of a coupled model. The MM, characterized by an anomalous north–south SST gradient and anomalous surface circulation in the northeasterly trade regime with maximum variance in boreal spring, is shown to be inherent to thermodynamic ocean–atmosphere coupling in the intertropical convergence zone (ITCZ) latitude, and the MM existence is independent of ENSO. The thermodynamic coupling enhances the persistence of the anomalous winds in the deep tropics, forcing energetic equatorially trapped oceanic waves to occur in the central western Pacific, which in turn initiate an ENSO event. The majority of ENSO events in both nature and the coupled model are preceded by MM events.
An Analysis of Tropical Ocean Diurnal Warm Layers
Authors: Bellenger Hugo , Duvel Jean-Philippe 
Published: January 2009

Abstract
During periods of light surface wind, a warm stable layer forms at the ocean surface with a maximum sea surface temperature (SST) in the early afternoon. The diurnal SST amplitude (DSA) associated with these diurnal warm layers (DWLs) can reach several degrees and impact the tropical climate variability. This paper first presents an approach to building a daily time series of the DSA over the tropics between 1979 and 2002. The DSA is computed over 2.5° of latitude–longitude regions using a simple DWL model forced by hourly-interpolated surface radiative and turbulent fluxes given by the 40-yr ECMWF Re-Analysis (ERA-40). One advantage of this approach is the homogeneity of the results given by the relative homogeneity of ERA-40. The approach is validated at the global scale using empirical DWL models reported in the literature and the Surface Velocity Program (SVP) drifters of the Marine Environmental Data Service (MEDS). For the SVP dataset, a new technique is introduced to derive the diurnal variation of the temperature from raw measurements.
This DWL time series is used to analyze the potential role of DWLs in the variability of the tropical climate. The perturbation of the surface fluxes by DWLs can give a cooling of the ocean mixed layer as large as 2.5 K yr−1 in some tropical regions. On a daily basis, this flux perturbation is often above 10 W m−2 and sometimes exceeds 50 W m−2. DWLs can be organized on regions up to a few thousand kilometers and can persist for more than 5 days. It is shown that strong DWLs develop above the equatorial Indian Ocean during the suppressed phase of the intraseasonal oscillation (ISO). DWLs may trigger large-scale convective events and favor the eastward propagation of the ISO convective perturbation during boreal winter. This study also suggests that the simple approach presented here may be used as a DWL parameterization for atmospheric general circulation models.
Correcting Unintended Perturbation Biases in Hydrologic Data Assimilation
Authors: Ryu Dongryeol , Crow Wade T. , Zhan Xiwu , Jackson Thomas J. 
Published: January 2009

Abstract
Hydrologic data assimilation has become an important tool for improving hydrologic model predictions by using observations from ground, aircraft, and satellite sensors. Among existing data assimilation methods, the ensemble Kalman filter (EnKF) provides a robust framework for optimally updating nonlinear model predictions using observations. In the EnKF, background prediction uncertainty is obtained using a Monte Carlo approach where state variables, parameters, and forcing data for the model are synthetically perturbed to explicitly simulate the error-prone representation of hydrologic processes in the model. However, it is shown here that, owing to the nonlinear nature of these processes, an ensemble of model forecasts perturbed by mean-zero Gaussian noise can produce biased background predictions. This ensemble perturbation bias in soil moisture states can lead to significant mass balance errors and degrade the performance of the EnKF analysis in deeper soil layers. Here, a simple method of bias correction is introduced in which such perturbation bias is corrected using an unperturbed model simulation run in parallel with the EnKF analysis. The proposed bias-correction scheme effectively removes biases in soil moisture and reduces soil water mass balance errors. The performance of the EnKF is improved in deeper layers when the filter is applied with the bias-correction scheme. The interplay of nonlinear hydrologic processes is discussed in the context of perturbation biases, and implications of the bias correction for real-data assimilation cases are presented.
Validation of a Dual-Pass Microwave Land Data Assimilation System for Estimating Surface Soil Moisture in Semiarid Regions
Authors: Yang Kun , Koike Toshio , Kaihotsu Ichirow , Qin Jun 
Published: January 2009

Abstract
This study examines the capability of a new microwave land data assimilation system (LDAS) for estimating soil moisture in semiarid regions, where soil moisture is very heterogeneous. This system assimilates the Advanced Microwave Scanning Radiometer for Earth Observing System (AMSR-E) 6.9- and 18.7-GHz brightness temperatures into a land surface model (LSM), with a radiative transfer model as an observation operator. To reduce errors caused by uncertainties of system parameters, the LDAS uses a dual-pass assimilation algorithm, with a calibration pass to estimate major model parameters from satellite data and an assimilation pass to estimate the near-surface soil moisture. Validation data of soil moisture were collected in a Mongolian semiarid region. Results show that (i) the LDAS-estimated soil moistures are comparable to areal averages of in situ measurements, though the measured soil moistures were highly variable from site to site; (ii) the LSM-simulated soil moistures show less biases when the LSM uses LDAS-calibrated parameter values instead of default parameter values, indicating that the satellite-based calibration does contribute to soil moisture estimations; and (iii) compared to the LSM, the LDAS produces more robust and reliable soil moisture when forcing data become worse. The lower sensitivity of the LDAS output to precipitation is particularly encouraging for applying this system to regions where precipitation data are prone to errors.
Nonstationary Westward Translation of Nonlinear Frontal Warm-Core Eddies
Authors: Rubino Angelo , Dotsenko Sergey , Brandt Peter 
Published: January 2009

Abstract
For the first time, an analytical theory and a very high-resolution, frontal numerical model, both based on the unsteady, nonlinear, reduced-gravity shallow water equations on a β plane, have been used to investigate aspects of the migration of homogeneous surface, frontal warm-core eddies on a β plane. Under the assumption that, initially, such vortices are surface circular anticyclones of paraboloidal shape and having both radial and azimuthal velocities that are linearly dependent on the radial coordinate (i.e., circular pulsons of the first order), approximate analytical expressions are found that describe the nonstationary trajectories of their centers of mass for an initial stage as well as for a mature stage of their westward migration. In particular, near-inertial oscillations are evident in the initial migration stage, whose amplitude linearly increases with time, as a result of the unbalanced vortex initial state on a β plane. Such an initial amplification of the vortex oscillations is actually found in the first stage of the evolution of warm-core frontal eddies simulated numerically by means of a frontal numerical model initialized using the shape and velocity fields of circular pulsons of the first order. In the numerical simulations, this stage is followed by an adjusted, complex nonstationary state characterized by a noticeable asymmetry in the meridional component of the vortex’s horizontal pressure gradient, which develops to compensate for the variations of the Coriolis parameter with latitude. Accordingly, the location of the simulated vortex’s maximum depth is always found poleward of the location of the simulated vortex’s center of mass. Moreover, during the adjusted stage, near-inertial oscillations emerge that largely deviate from the exactly inertial ones characterizing analytical circular pulsons: a superinertial and a subinertial oscillation in fact appear, and their frequency difference is found to be an increasing function of latitude. A comparison between vortex westward drifts simulated numerically at different latitudes for different vortex radii and pulsation strengths and the corresponding drifts obtained using existing formulas shows that, initially, the simulated vortex drifts correspond to the fastest predicted ones in many realistic cases. As time elapses, however, the development of a β-adjusted vortex structure, together with the effects of numerical dissipation, tend to slow down the simulated vortex drift.
Role of Eddy Forcing in the Dynamics of Multiple Zonal Jets in a Model of the North Atlantic
Authors: Kamenkovich Igor , Berloff Pavel , Pedlosky Joseph 
Published: January 2009

Abstract
Multiple zonal jets are observed in satellite data–based estimates of oceanic velocities, float measurements, and high-resolution numerical simulations of the ocean circulation. This study makes a step toward understanding the dynamics of these jets in the real ocean by analyzing the vertical structure and dynamical balances within multiple zonal jets simulated in an eddy-resolving primitive equation model of the North Atlantic. In particular, the authors focus on the role of eddy flux convergences (“eddy forcing”) in supporting the buoyancy and relative/potential vorticity (PV) anomalies associated with the jets. The results suggest a central role of baroclinic eddies in the barotropic and baroclinic dynamics of the jets, and significant differences in the effects of eddy forcing between the subtropical and subpolar gyres. Additionally, diabatic potential vorticity sources and sinks, associated with vertical diffusion, are shown to play an important role in supporting the potential vorticity anomalies. The resulting potential vorticity profile does not resemble a “PV staircase”—a distinct meridional structure observed in some idealized studies of geostrophic turbulence.
A New Technique for Estimation of Lower-Tropospheric Temperature and Water Vapor Profiles from Radio Occultation Refractivity
Authors: Jagadheesha D. , Simon B. , Pal P-K. , Joshi P. C. , Maheshwari A. 
Published: January 2009

Abstract
An empirical technique is proposed to obtain temperature and humidity profiles over the tropics using radio occultation refractivity profiles and surface/available lower-altitude temperature and pressure measurements over humid tropical regions. The technique is tested on a large number of diverse radiosonde-derived refractivity profiles over the tropics (30°S–30°N) and selected Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) radio occultation refractivity profiles that have collocated radiosonde observations over the region 10°S–30°N during the boreal summer of 2006. In a number of cases, the results were in good agreement with the collocated radiosonde data. The error statistics of temperature and humidity profiles obtained from the proposed technique are discussed and compared with the previously published results from another technique and also with the results of a one-dimensional variational data assimilation (1DVAR) technique given with COSMIC data. It is found that the previously published results and proposed technique are marginally better (worse) in reproducing observed relative humidity (specific humidity) when compared to the 1DVAR technique. The proposed new technique is applied on COSMIC refractivity profiles over the Bay of Bengal during summer 2007 to derive changes in vertical thermal and moisture changes in the troposphere between active and break phases of the monsoon pattern and many of the observed features are captured reasonably well.