3,691 research outputs found
Features of Fast Neutrons in Dark Matter Searches
Diffractive scattering of "fast" or "high energy" neutrons, can give low
energy nuclear recoils in the signal region for dark matter searches. We
present a discussion using the 'black disc' model. This permits a simple and
general, although approximate, description of this possible background. We note
a number of its features. In particular there are mass number A dependent
aspects which can be studied in setups where events on different nuclei are
observable at the same time. These include the recoil energy distributions, and
the A behavior of the cross section. We define a parameter which
characterizes the recoil energy to be expected due to fast neutrons. It ranges
from 100 keV on light nuclei to a few keV on heavy nuclei, and a general
treatment is possible in terms of it, within the 'black disc' approximation. In
addition, the presence of inelastic processes would be characteristic of fast
neutrons.Comment: new version with numerous small corrections and clarifications.
Improved figures and references. No essential changes in conten
Measuring the Temperature of a Mesoscopic Quantum Electron System by means of Single Electron Statistics
We measure the temperature of a mesoscopic system consisting of an
ultra-dilute two dimensional electron gas at the interface in a
metal-oxide-semiconductor field effect transistor (MOSFET) quantum dot by means
of the capture and emission of an electron in a point defect close to the
interface. Contrarily to previous reports, we show that the capture and
emission by point defects in Si n-MOSFETs can be temperature dependent down to
800 mK. As the finite quantum grand canonical ensemble model applies, the time
domain charge fluctuation in the defect is used to determine the temperature of
the few electron gas in the channel.Comment: 4 Figures (color
Entangling macroscopic diamonds at room temperature: Bounds on the continuous-spontaneous-localization parameters
A recent experiment [K. C. Lee et al., Science 334, 1253 (2011)] succeeded in
detecting entanglement between two macroscopic specks of diamonds, separated by
a macroscopic distance, at room temperature. This impressive results is a
further confirmation of the validity of quantum theory in (at least parts of)
the mesoscopic and macroscopic domain, and poses a challenge to collapse
models, which predict a violation of the quantum superposition principle, which
is the bigger the larger the system. We analyze the experiment in the light of
such models. We will show that the bounds placed by experimental data are
weaker than those coming from matter-wave interferometry and
non-interferometric tests of collapse models.Comment: 7 pages, 3 figures, v2: close to the published version, LaTe
Financial maturity concepts with application to three hardwood timber stands
Timber is âfinancially matureâ when its rate of value increase falls below what the landowner can earn in alternative investments that are comparable in duration, risk, liquidity, and other factors. The basic concept of financial maturity is simple, but in application it involves several very important, basic questions and issues
Ultrastructural aspects of two different mast cell populations in human healthy gingival tissue
The results of our recent microscopy studies clearly have demonstrated the constant presence of numerous metachromatic cells in healthy human gingival connective tissue. Despite the great number of studies on mast cell population in many human organs (lung, skin, uterus, and bowel), at the present time few are the studies regarding the morphostructural aspects of mast cells in the human gingiva. The aim of this study was to assess by transmission electron microscopy the presence of mast cells in the healthy human gingiva and to characterize the ultrastructural aspects of mast cells populations. 30 specimens of human gingival tissue were collected from 30 patients with informed consent. The samples were prepared for T.E.M. examination. In all the ultrathin sections observed we detected numerous and ubiquitarious mast cells. These exhibited several morphological types of cytoplasmic granules with characteristic subgranular architectural variety in shape and density. This allowed us to divide mast cells into two groups: cells with granules consisted of compact coiled scrolls, fine granular material and lattice - grating configuration, and cells containing granules with discrete scrolls formed by more concentric lamellae and particulate structure. The two ultrastructural aspects observed correspond to McTC and McT of the international literature. Therefore in the human gingival connective tissue, like in other organs, two types of mast cells are clearly present. Surprisingly, the human gingival tissue shows, like the lung, McT as the prevailing subpopulation, in contrast to the skin, uterus and gastrointestinal submucosa where McTC prevail. Dans le cadre dâune Ă©tude sur la population cellulaire du tissu conjonctif gingival humain nous avons constatĂ©, en microscopie optique, la prĂ©sence constante de nombreuses cellules metachromatiques. Pour dĂ©finir la nature de telles cellules et pour en dĂ©terminer les aspects ultra-structuraux, nous avons Ă©tudiĂ© au microscope Ă©lectronique Ă transmission 30 biopsies du tissu gingival humain, cliniquement sain. Dans tous les Ă©chantillons examinĂ©s nous avons observĂ© de nombreux mastocytes dont le contenu granulaire nous est apparu caractĂ©risĂ© par un aspect « Ă particules » et « en rouleaux » ou bien, dans dâautres Ă©lĂ©ments cellulaires, par un aspect «en grillage». Les deux aspects ultrastructuraux dĂ©crits nous permettent de distinguer les mastocytes gingivaux en deux sous-populations, diffĂ©rentes comme lâont confirmĂ© plusieurs auteurs, selon la localisation anatomique, selon la structure intĂ©rieure et le contenu enzymatique des granules, et, enfin, selon la rĂ©action Ă des substances sĂ©crĂ©tagogues
Fireballs Loading and the Blast Wave Model of Gamma Ray Bursts
A simple function for the spectral power
is proposed to model, with 9 parameters, the spectral and temporal evolution of
the observed nonthermal synchrotron power flux from GRBs in the blast wave
model. Here mc is the observed dimensionless photon
energy and is the observing time. Assumptions and an issue of lack of
self-consistency are spelled out. The spectra are found to be most sensitive to
the baryon loading, expressed in terms of the initial bulk Lorentz factor
, and an equipartition term which is assumed to be constant in
time and independent of . Expressions are given for the peak spectral
power at the photon energy of the spectral power peak. A general rule is that the total
fireball particle kinetic energy , where is the deceleration time scale and is the maximum measured bolometric
power output in radiation, during which it is carried primarily by photons with
energy .Comment: 26 pages, including 4 figures, uses epsf.sty, rotate.sty; submitted
to ApJ; revised version with extended introduction, redrawn figures, and
correction
Response of CdWO4 crystal scintillator for few MeV ions and low energy electrons
The response of a CdWO4 crystal scintillator to protons, alpha particles, Li,
C, O and Ti ions with energies in the range 1 - 10 MeV was measured. The
non-proportionality of CdWO4 for low energy electrons (4 - 110 keV) was studied
with the Compton Coincidence Technique. The energy dependence of the quenching
factors for ions and the relative light yield for low energy electrons was
calculated using a semi-empirical approach. Pulse-shape discrimination ability
between gamma quanta, protons, alpha particles and ions was investigated.Comment: 20 pages, 8 figs, accepted in Nucl. Instrum. Meth.
Hida Scan in The Follow-Up of Biliary-Enteric Anastomoses
In order to assess the patency and function of biliary-enteric anastomoses performed in our Department of
Surgery, 21 patients entered the following study, provided an informed consent was obtained. All the
patients were affected by benign biliary tract diseases and underwent either Roux-en-Y
hepaticojejunostomy (11 cases), or side-to-side choledochoduodenostomy (10 cases). The 21 patients
were evaluated with Tc-99m-HIDA scanning at intervals of 20 daysâ36 months after the surgical
procedure (mean 14 months). The images were obtained after intravenous injection of the radioactive
medium (5 mCi) and the scans were taken at 1 min (1 frame/s), 3 min (1 frame/10 s), and 56 min (1 frame/2
min). The data were analyzed by a Digital PDP 11/34 Computer System. This method allowed us to assess
each individual patient for the patency of the anastomosis and, by computer analysis, to build up a profile
of the timing of the passage of the radioactive medium through the anastomosis; a delayed passage across
the anastomosis was always pathological
Correlating densities of centrality and activities in cities : the cases of Bologna (IT) and Barcelona (ES)
This paper examines the relationship between street centrality and densities of commercial and service activities in cities. The aim is to verify whether a correlation exists and whether some 'secondary' activities, i.e. those scarcely specialized oriented to the general public and ordinary daily life, are more linked to street centrality than others. The metropolitan area of Barcelona (Spain) is investigated, and results are compared with those found in a previous work on the city of Bologna (Italy). Street centrality is calibrated in a multiple centrality assessment (MCA) model composed of multiple measures such as closeness, betweenness and straightness. Kernel density estimation (KDE) is used to transform data sets of centrality and activities to one scale unit for correlation analysis between them. Results indicate that retail and service activities in both Bologna and Barcelona tend to concentrate in areas with better centralities, and that secondary activities exhibit a higher correlation
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