Dependences of the Casimir-Polder interaction between an atom and a cavity wall on atomic and material properties

The Casimir-Polder and van der Waals interactions between an atom and a flat cavity wall are investigated under the influence of real conditions including the dynamic polarizability of the atom, actual conductivity of the wall material and nonzero temperature of the wall. The cases of different atoms near metal and dielectric walls are considered. It is shown that to obtain accurate results for the atom-wall interaction at short separations, one should use the complete tabulated optical data for the complex refractive index of the wall material and the accurate dynamic polarizability of an atom. At relatively large separations in the case of a metal wall, one may use the plasma model dielectric function to describe the dielectric properties of wall material. The obtained results are important for the theoretical interpretation of experiments on quantum reflection and Bose-Einstein condensation.Comment: 5 pages, 1 figure, iopart.cls is used, to appear in J. Phys. A (special issue: Proceedings of QFEXT05, Barcelona, Sept. 5-9, 2005

Compliance of the L5-S1 spinal unit: a comparative study between an unconstrained and a partially constrained system

A comparison between an unconstrained and a partially constrained system for in vitro biomechanical testing of the L5-S1 spinal unit was conducted. The objective was to compare the compliance and the coupling of the L5-S1 unit measured with an unconstrained and a partially constrained test for the three major physiological motions of the human spine. Very few studies have compared unconstrained and partially constrained testing systems using the same cadaveric functional spinal units (FSUs). Seven human L5-S1 units were therefore tested on both a pneumatic, unconstrained, and a servohydraulic, partially constrained system. Each FSU was tested along three motions: flexion-extension (FE), lateral bending (LB) and axial rotation (AR). The obtained kinematics on both systems is not equivalent, except for the FE case, where both motions are similar. The directions of coupled motions were similar for both tests, but their magnitudes were smaller in the partially constrained configuration. The use of a partially constrained system to characterize LB and AR of the lumbosacral FSU decreased significantly the measured stiffness of the segment. The unconstrained system is today's "gold standard” for the characterization of FSUs. The selected partially constrained method seems also to be an appropriate way to characterize FSUs for specific applications. Care should be taken using the latter method when the coupled motions are importan

Dependences of the van der Waals atom-wall interaction on atomic and material properties

The 1%-accurate calculations of the van der Waals interaction between an atom and a cavity wall are performed in the separation region from 3 nm to 150 nm. The cases of metastable He${}^{\ast}$ and Na atoms near the metal, semiconductor or dielectric walls are considered. Different approximations to the description of wall material and atomic dynamic polarizability are carefully compared. The smooth transition to the Casimir-Polder interaction is verified. It is shown that to obtain accurate results for the atom-wall van der Waals interaction at shortest separations with an error less than 1% one should use the complete optical tabulated data for the complex refraction index of the wall material and the accurate dynamic polarizability of an atom. The obtained results may be useful for the theoretical interpretation of recent experiments on quantum reflection and Bose-Einstein condensation of ultracold atoms on or near surfaces of different nature.Comment: 14 pages, 5 figures, 3 tables, accepted for publication in Phys. Rev.

Carotid wall stress calculated with continuous intima-media thickness assessment using B-mode ultrasound

Cardiovascular risk is normally assessed using clinical risk factors but it can be refined using non-invasive infra-clinical markers. Intima-Media Thickness (IMT) is recognized as an early indicator of cardiovascular disease. Carotid Wall Stress (CWS) can be calculated using arterial pressure and carotid size (diameter and IMT). Generally, IMT is measured during diastole when it reaches its maximum value. However, it changes during the cardiac cycle and a time-dependant waveform can be obtained using B-mode ultrasound images. In this work we calculated CWS considering three different approaches for IMT assessment: (i) constant IMT (standard diastolic value), (ii) estimated IMT from diameter waveform (assuming a constant cross-sectional wall area) and (iii) continuously measured IMT. Our results showed that maximum wall stress depends on the IMT estimation method. Systolic CWS progressively increased using the three approaches (p<0.024). We conclude that maximum CWS is highly dependent on wall thickness and accurate IMT measures during systole should be encouraged.Fil: Pascaner, Ariel Fernando. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Favaloro; ArgentinaFil: Craiem, Damian. Universidad Favaloro; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Casciaro, Mariano Ezequiel. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Favaloro; ArgentinaFil: Danielo, R.. Fundación Favaloro; ArgentinaFil: Graf Caride, Diego Sebastián. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Favaloro; ArgentinaFil: Guevara, E.. Fundación Favaloro; Argentin

Thermal quantum field theory and the Casimir interaction between dielectrics

The Casimir and van der Waals interaction between two dissimilar thick dielectric plates is reconsidered on the basis of thermal quantum field theory in Matsubara formulation. We briefly review two main derivations of the Lifshitz formula in the framework of thermal quantum field theory without use of the fluctuation-dissipation theorem. A set of special conditions is formulated under which these derivations remain valid in the presence of dissipation. The low-temperature behavior of the Casimir and van der Waals interactions between dissimilar dielectrics is found analytically from the Lifshitz theory for both an idealized model of dilute dielectrics and for real dielectrics with finite static dielectric permittivities. The free energy, pressure and entropy of the Casimir and van der Waals interactions at low temperatures demonstrate the same universal dependence on the temperature as was previously discovered for ideal metals. The entropy vanishes when temperature goes to zero proving the validity of the Nernst heat theorem. This solves the long-standing problem on the consistency of the Lifshitz theory with thermodynamics in the case of dielectric plates. The obtained asymptotic expressions are compared with numerical computations for both dissimilar and similar real dielectrics and found to be in excellent agreement. The role of the zero-frequency term in Matsubara sum is investigated in the case of dielectric plates. It is shown that the inclusion of conductivity in the model of dielectric response leads to the violation of the Nernst heat theorem. The applications of this result to the topical problems of noncontact atomic friction and the Casimir interaction between real metals are discussed.Comment: 39 pages, 4 figures, to appear in Phys. Rev.

A theory of Plasma Membrane Calcium Pump stimulation and activity

The ATP-driven Plasma Membrane Calcium pump or Ca(2+)-ATPase (PMCA) is characterized by a high affinity to calcium and a low transport rate compared to other transmembrane calcium transport proteins. It plays a crucial role for calcium extrusion from cells. Calmodulin is an intracellular calcium buffering protein which is capable in its Ca(2+) liganded form of stimulating the PMCA by increasing both the affinity to calcium and the maximum calcium transport rate. We introduce a new model of this stimulation process and derive analytical expressions for experimental observables in order to determine the model parameters on the basis of specific experiments. We furthermore develop a model for the pumping activity. The pumping description resolves the seeming contradiction of the Ca(2+):ATP stoichiometry of 1:1 during a translocation step and the observation that the pump binds two calcium ions at the intracellular site. The combination of the calcium pumping and the stimulation model correctly describes PMCA function. We find that the processes of calmodulin-calcium complex attachment to the pump and of stimulation have to be separated. Other PMCA properties are discussed in the framework of the model. The presented model can serve as a tool for calcium dynamics simulations and provides the possibility to characterize different pump isoforms by different type-specific parameter sets.Comment: 24 pages, 6 figure

Exact Casimir-Polder potential between a particle and an ideal metal cylindrical shell and the proximity force approximation

We derive the exact Casimir-Polder potential for a polarizable microparticle inside an ideal metal cylindrical shell using the Green function method. The exact Casimir-Polder potential for a particle outside a shell, obtained recently by using the Hamiltonian approach, is rederived and confirmed. The exact quantum field theoretical result is compared with that obtained using the proximity force approximation and a very good agreement is demonstrated at separations below 0.1$R$, where $R$ is the radius of the cylinder. The developed methods are applicable in the theory of topological defects.Comment: 8 pages, 4 figures, Accepted for publication in Eur. Phys. J.

Hydrographic variability (1994-2020) in the Ría de Vigo and adjacent shelf (NW Iberia)

The Spanish Institute of Oceanography (IEO-CSIC) carries out monthly oceanographic samplings at across-shelf sections off the northern Spanish coast under the monitoring program RADIALES (https://www.seriestemporales-ieo.net/). This is a multidisciplinary marine research effort addressing long-term variability issues at the ecosystem level (Bode et al., 2015; Valdés et al., 2002). Currently, the monitoring program includes 5 perpendicular coastal transects in Northern Spain: Santander, Gijón, Cudillero, A Coruña and Vigo. Focusing on the section located in the Ría de Vigo and adjacent shelf, we have analysed a 27-year time series (1994 - 2020) of temperature and salinity obtained through CTD profiles in three stations, two inside the Ría (~30 and ~40 m depth) and one in the mid-shelf (~90 m depth). This study summarizes the hydrographic variability in the region through the construction of a local climatology. In addition, long-term trends and interannual changes in seasonality are examined. The results show a change in the salinity regime in medium depth waters in 2013, although not in temperature. Near the surface, the temperature undergoes a negative shift from 2016, in correspondence with the entry of the AMO into a new negative phase

Megrim (Lepidorhombus whiffiagonis) weight-length relationships in the northern Bay of Biscay and Celtic Sea

The weight-length relationships are of a great interest in fish biology, stock assessment and fishery management, by predicting weight from length information and allowing to estimate the stock biomass. Weight-length relationships of megrim (Lepidorhombus whiffiagonis), an economically relevant flatfish species, are studied for two decades (2001 to 2019) in northern Bay of Biscay and Celtic Sea (ICES stock Div. 7.b-k, 8.abd), two important European fishing areas. More than 22000 specimens collected from commercial landings by AZTI and IEO were sampled. Total fish length, total weight and commercial gutted weight were obtained. Four five-year periods (quinquennium) (2000-04; 2005-09; 2010-14; 2015-19) were defined in the studied time-series. Both the large sample size and time-series available, as well as the collaboration between both institutions collecting complementary information from this stock, allowed obtaining robust somatic parameters and analyzing their temporal variations. A weight-length relationship model was fitted and the quinquennium and semester factors, which are of interest biologically and for assessment purposes, and their interactions were significant in the preliminary model. The weight-length relationships, both for total and gutted weight and for the combined sexes of the most recent quinquennium are presented in this work and considered the most suitable to be used in the oncoming annual assessment process of the status of this stock in northern Bay of Biscay and Celtic Sea in ICES

Age determination procedures on small and medium pelagic species in Spanish Institute of Oceanography (IEO)

This handbook presents a summary of the age estimation procedures used in Spanish Institute of Oceanography (IEO) for some of the main commercial small and medium pelagic species of the Spanish fleet: anchovy (Engraulis encrasicolus), sardine (Sardina pichardus), mackerel (Scomber scombrus), chuck mackerel (Scomber colias), horse mackerel (Trachurus trachurus), Mediterranean horse mackerel (Trachurus mediterraneus) and blue whiting (Micromesistius poutassou). It provides information about the sampling program, otolith extraction and preparation, and the age estimation criteria. A summary of the information related to the age accuracy, validation and corroboration of each species is also presented, as well as that related to the age precision, quality control and verification