Density profiles and collective excitations of a trapped two component Fermi vapour

We discuss the ground state and the small-amplitude excitations of a degenerate vapour of fermionic atoms placed in two hyperfine states inside a spherical harmonic trap. An equations-of-motion approach is set up to discuss the hydrodynamic dissipation processes from the interactions between the two components of the fluid beyond mean-field theory and to emphasize analogies with spin dynamics and spin diffusion in a homogeneous Fermi liquid. The conditions for the establishment of a collisional regime via scattering against cold-atom impurities are analyzed. The equilibrium density profiles are then calculated for a two-component vapour of 40K atoms: they are little modified by the interactions for presently relevant values of the system parameters, but spatial separation of the two components will spontaneously arise as the number of atoms in the trap is increased. The eigenmodes of collective oscillation in both the total particle number density and the concentration density are evaluated analytically in the special case of a symmetric two-component vapour in the collisional regime. The dispersion relation of the surface modes for the total particle density reduces in this case to that of a one-component Fermi vapour, whereas the frequencies of all other modes are shifted by the interactions.Comment: 14 pages, 4 figure

Fiber link design considerations for cloud-Radio Access Networks

Analog radio over fiber (RoF) links may offer advantages for cloud-Radio Access Networks in terms of component cost, but the behavior of the distortion with large numbers of subcarriers needs to be understood. In this paper, this is presented in terms of the variation between subcarriers. Memory polynomial predistortion is also shown to compensate for RoF and wireless path distortion. Whether for digitized or analog links, it is shown that appropriate framing structure parameters must be used to assure performance, especially of time-division duplex systems

Analysis of the indoor air quality in Greek primary schools

The exposure of children to indoor air pollutants in school classrooms might cause them adverse health effects. In order to confront this issue, the in-depth study and evaluation of the indoor air quality in classrooms is necessary. The aims of this study are to characterize the environmental factors that affect indoor air quality. Several indoor air pollutants such as the concentrations of the particulate matter (PM) of several different size ranges, carbon dioxide (CO2), carbon monoxide (CO) and VOCs, were simultaneously measured in classrooms as well as the outdoor environment in nine primary schools in Athens, Greece during April 2013. Measurements were performed for more than 7 hours per day, for a period of one to five days in a classroom, per school. The first results indicate extreme PM10 concentrations in many cases with varying fluctuations throughout the day, mainly attributed to the presence of students, inadequate level of ventilation and chalk dust while the ultrafine particles (UFP) remained in rather low levels. In most of the cases the indoor concentrations exceeded the outdoor ones by more than ten times. Carbon dioxide concentrations in many cases exceeded the recommended limit value indicating inadequate levels of ventilation

A study on the thermal environment in Greek primary schools based on questionnaires and concurrent measurements

The present study investigates the indoor thermal comfort perceived by students through a questionnaire survey conducted during spring 2013 in naturally ventilated primary schools in Athens. Thermal environment parameters such as air temperature, relative humidity, air velocity and mean radiant temperature were simultaneously measured. Then, Fanger’s indices of Predicted Mean Vote (PMV) and Percentage of People Dissatisfied (PPD) were calculated by using clothing and metabolic rates. The main purpose of this work is the evaluation of the ability of the answers from students to be sufficient to assess the thermal environment of classrooms. The possible associations between subjective thermal sensation votes and objective measurements are examined by comparing students’ answers based on the seven point thermal sensation scale and the results taken by the calculated indices of PMV and PPD

Indoor and outdoor distribution of airborne pollutants in naturally ventilated classrooms

The present study aims at investigating concentration levels of particulate matter PM10, PM2.5, PM1 and UFP as well as of total airborne fungi and their vertical distribution in the indoor and outdoor environment of school classrooms. Measurements were performed in two naturally ventilated high schools in Athens, from January until May 2011. Indoor concentrations of the pollutants will be presented per floor level and indoor to outdoor (I/O) concentration ratios will be estimated as a function of the floor height. The ultimate goal is to create variations’ profile of I/O pollutant ratios, so as to understand the contribution of indoor sources and the extent to which the indoor air quality is being affected by the outdoor pollutants

Does indoor environmental quality affect students' performance?

There is little knowledge on if and how indoor environmental quality influences students’ attendance and productivity. However, this issue has been of growing interest the recent years in the scientific community and results are showing that student learning performance is significantly affected by indoor environmental quality factors. In the present study the learning performance is examined through numerical test scores achieved by primary school students in their classrooms. The assessment of indoor environmental quality parameters such as thermal, visual, acoustic and air quality and the evaluation of Sick Building Syndrome (SBS) symptoms was conducted through questionnaires handed out to the same sample of students. Main objective of this paper is to investigate whether the degradation of the indoor environmental quality can impact the overall performance of students

The (234)U neutron capture cross section measurement at the n_TOF facility

The neutron capture cross-section of (234)U has been measured for energies from thermal up to the keV region in the neutron time-of-flight facility n_TOF, based on a spallation source located at CERN. A 4 pi BaF(2) array composed of 40 crystals, placed at a distance of 184.9 m from the neutron source, was employed as a total absorption calorimeter (TAC) for detection of the prompt gamma-ray cascade from capture events in the sample. This text describes the experimental setup, all necessary steps followed during the data analysis procedure. Results are presented in the form of R-matrix resonance parameters from fits with the SAMMY code and compared to the evaluated data of ENDF in the relevant energy region, indicating the good performance of the n_TOF facility and the TAC

Measurements of high-energy neutron-induced fission of (nat)Pb and (209)Bi

This is an Open Access article distributed under the terms of the Creative Commons Attribution-Noncommercial License 3.0, which permits unrestricted use, distribution, and reproduction in any noncommercial medium, provided the original work is properly citedThe CERN Neutron Time-Of-Flight (n_TOF) facility is well suited to measure low cross sections as those of neutron-induced fission in subactinides. The cross section ratios of (nat)Pb and (209)Bi relative to (235)U and (238)U were measured using PPAC detectors and a fragment coincidence method that allows us to identify the fission events. The present experiment provides first results for neutron-induced fission up to 1 GeV. Good agreement is found with previous experimental data below 200 MeV. The comparison with proton-induced fission indicates that the limiting regime where neutron-induced and proton-induced fission reach equal cross sections is close to 1 GeV

Measurement of the (90,91,92,93,94,96)Zr(n,gamma) and (139)La(n,gamma) cross sections at n_TOF

Open AccessNeutron capture cross sections of Zr and La isotopes have important implications in the field of nuclear astrophysics as well as in the nuclear technology. In particular the Zr isotopes play a key role for the determination of the neutron density in the He burning zone of the Red Giant star, while the (139)La is important to monitor the s-process abundances from Ba up to Ph. Zr is also largely used as structural materials of traditional and advanced nuclear reactors. The nuclear resonance parameters and the cross section of (90,91,92,93,94,96)Zr and (139)La have been measured at the n_TOF facility at CERN. Based on these data the capture resonance strength and the Maxwellian-averaged cross section were calculated

Measurement of the neutron capture cross section of the s-only isotope 204Pb from 1 eV to 440 keV

The neutron capture cross section of 204Pb has been measured at the CERN n_TOF installation with high resolution in the energy range from 1 eV to 440 keV. An R-matrix analysis of the resolved resonance region, between 1 eV and 100 keV, was carried out using the SAMMY code. In the interval between 100 keV and 440 keV we report the average capture cross section. The background in the entire neutron energy range could be reliably determined from the measurement of a 208Pb sample. Other systematic effects in this measurement could be investigated and precisely corrected by means of detailed Monte Carlo simulations. We obtain a Maxwellian average capture cross section for 204Pb at kT=30 keV of 79(3) mb, in agreement with previous experiments. However our cross section at kT=5 keV is about 35% larger than the values reported so far. The implications of the new cross section for the s-process abundance contributions in the Pb/Bi region are discussed.Comment: 8 pages, 3 figures, article submitted to Phys. Rev.