8,039 research outputs found
Inelastic collisions in an exactly solvable two-mode Bose-Einstein Condensate
Inelastic collisions occur in Bose-Einstein condensates, in some cases,
producing particle loss in the system. Nevertheless, these processes have not
been studied in the case when particles do not escape the trap. We show that
such inelastic processes are relevant in quantum properties of the system such
as the evolution of the relative population, the self trapping effect and the
probability distribution of particles. Moreover, including inelastic terms in
the model of the two-mode condensate allows for an exact analytical solution.
Using this solution, we show that collisions favor the generation of
entanglement between the modes of the condensate as long as the collision rate
does not exceed the natural frequency of the system
Noise-induced phase transitions: Effects of the noises' statistics and spectrum
The local, uncorrelated multiplicative noises driving a second-order, purely
noise-induced, ordering phase transition (NIPT) were assumed to be Gaussian and
white in the model of [Phys. Rev. Lett. \textbf{73}, 3395 (1994)]. The
potential scientific and technological interest of this phenomenon calls for a
study of the effects of the noises' statistics and spectrum. This task is
facilitated if these noises are dynamically generated by means of stochastic
differential equations (SDE) driven by white noises. One such case is that of
Ornstein--Uhlenbeck noises which are stationary, with Gaussian pdf and a
variance reduced by the self-correlation time (\tau), and whose effect on the
NIPT phase diagram has been studied some time ago. Another such case is when
the stationary pdf is a (colored) Tsallis' (q)--\emph{Gaussian} which, being a
\emph{fat-tail} distribution for (q>1) and a \emph{compact-support} one for
(q<1), allows for a controlled exploration of the effects of the departure from
Gaussian statistics. As done before with stochastic resonance and other
phenomena, we now exploit this tool to study--within a simple mean-field
approximation and with an emphasis on the \emph{order parameter} and the
``\emph{susceptibility}''--the combined effect on NIPT of the noises'
statistics and spectrum. Even for relatively small (\tau), it is shown that
whereas fat-tail noise distributions ((q>1)) counteract the effect of
self-correlation, compact-support ones ((q<1)) enhance it. Also, an interesting
effect on the susceptibility is seen in the last case.Comment: 6 pages, 10 figures, uses aipproc.cls, aip-8s.clo and aipxfm.sty. To
appear in AIP Conference Proceedings. Invited talk at MEDYFINOL'06 (XV
Conference on Nonequilibrium Statistical Mechanics and Nonlinear Physics
Stochastic Resonance: influence of a noise spectrum
Here, in order to study \textit{stochastic resonance} (SR) in a double-well
potential when the noise source has a spectral density of the form
with varying , we have extended a procedure, introduced
by Kaulakys et al (Phys. Rev. E \textbf{70}, 020101 (2004)). In order to have
an analytical understanding of the results, we have obtained an effective
Markovian approximation, that allows us to make a systematic study of the
effect of such kind of noises on the SR phenomenon. The comparison of numerical
and analytical results shows an excellent qualitative agreement indicating that
the effective Markovian approximation is able to correctly describe the general
trends.Comment: 11 pages, 6 figures, submitted to Euro.Phys.J.
Increased intestinal carbonate precipitate abundance in the sea bream (Sparus aurata L.) in response to ocean acidification
Marine fish contribute to the carbon cycle by producing mineralized intestinal precipitates generated as by-products of their osmoregulation. Here we aimed at characterizing the control of epithelial bicarbonate secretion and intestinal precipitate presence in the gilthead sea bream in response to predicted near future increases of environmental CO2. Our results demonstrate that hypercapnia (950 and 1800 μatm CO2) elicits higher intestine epithelial HCO3- secretion ex vivo and a subsequent parallel increase of intestinal precipitate presence in vivo when compared to present values (440 μatm CO2). Intestinal gene expression analysis in response to environmental hypercapnia revealed the up-regulation of transporters involved in the intestinal bicarbonate secretion cascade such as the basolateral sodium bicarbonate co-transporter slc4a4, and the apical anion transporters slc26a3 and slc26a6 of sea bream. In addition, other genes involved in intestinal ion uptake linked to water absorption such as the apical nkcc2 and aquaporin 1b expression, indicating that hypercapnia influences different levels of intestinal physiology. Taken together the current results are consistent with an intestinal physiological response leading to higher bicarbonate secretion in the intestine of the sea bream paralleled by increased luminal carbonate precipitate abundance and the main related transporters in response to ocean acidification.Agência financiadora
Fundacao para a Ciencia e a Tecnologia (FCT)
SFRH/BD/113363/2015
PTDC/MAR-BIO/3034/2014
Fundacao para a Ciencia e a Tecnologia (FCT)
UID/Multi/04326/2019
Ministry of Science and Higher Education, Polandinfo:eu-repo/semantics/publishedVersio
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Potential of short wavelength laser ablation of organic materials
Although the literature contains several articles on UV laser ablation of synthetic polymers [1] and human tissue for surgical applications, to our knowledge there is no published record on organic geochemical applications for UV laser pyrolysis–gas chromatography–mass spectrometry (LA-GC-MS). In this study we have demonstrated the use of a 213 nm UV laser beam for ablating kerogens and organic rich rocks to liberate and analyse hydrocarbon signatures and compared the results against IR laser pyrolysis and traditional Py-GC-MS. It is possible to equate laser wavelength to electron volts where 1064 nm (IR) = 1.2 eV and 213 nm (UV) = 5.8 eV. Most chemical bonds have an energy between 2-4 eV and C-C bonds are ~3.6 eV. Organic materials can absorb radiation from a UV laser and chemical bonds can be cleaved cleanly by complex photochemical pathways by a single photon [2]. Ablation occurs with almost no heating of the sample and hence the term laser ablation instead of pyrolysis. Visible or IR lasers have insufficient energy to break bonds with a single photon this results in the heating of sample by the absobtion of energy into the vibrational modes of the molecule which can then result in pyrolysis. A solvent-extracted kerogen consisting mainly of higher plant material (Brownie Butte, Montanna, ~ 70 Ma) was used for initial experiments. A number of other samples have also been analysed. Laser ablation work was performed off-line in a static helium cell followed by solvent extraction of the laser cell. Separate analysis of the same samples using a more traditional flash pyrolysis approach was performed with a CDS pyroprobe and IR laser pyrolysis [3] for comparative purposes. As can be seen in Fig 1 UV laser ablation is able to liberate relatively high molecular weight fragments with no alkenes or other pyrolysis artefacts detected. SEM images of ablation pits indicate there is no obvious thermal alteration of the sample. The results of the pyrolysis techniques (on-line and IR laser pyrolysis) are similar and display a number of artefacts related to the pyrolysis process. Laser ablation of a number of samples has also shown that the distributions of biomarkers are comparable with the solvent extracts. Product yields although not quantified appear to be much higher than traditional pyrolysis technique
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Is UV laser ablation a suitable tool for geochemical analysis of organic rich source materials?
Abstract not available
Impact of a Culturally-Relevant Support Program and Latinx Adolescents\u27 Help Seeking Services: An Academic-Latinx Community Service Partnership To Enhance Culturally Responsive Services for Latinx Immigrant Youth.
Latinxs, in general, report logistical barriers that contribute to utilizing fewer healthcare services and/or not knowing how to navigate the healthcare system. In addition to underutilizing healthcare services, Latinx immigrant youth also report higher levels of negative attitudes towards mental health. However, little is still known regarding factors that impact these attitudes with Latinx immigrant youth, as well as the community support efforts that are available to this specific group. Using a semi-structured interview on 12 Latinx immigrant youth, this master’s thesis explored: (1) the attitudes towards mental health, (2) attitudes towards mental health services, (3) and the experiences of participating in a local community-based program for Latinx immigrant youth. Results found that most participants (83%) held positive attitudes toward mental health and all participants (100%) described positive attitudes towards mental health services. In addition, all participants reported having positive experiences with a culturally-sensitive youth program that promotes psychological well-being while integrating to the United States and noted that it had benefited them socially, culturally, and psychologically. Given the rise of Latinxs in the U.S., and the stigma surrounding mental health attitudes, it is important to continue to explore this area to better serve Latinx immigrant youth and connect them to mental health services they may need. Also, it is important to have community programs, such as this local youth program, that provide support and meet the needs of Latinx immigrant youth
Spectroscopic Signatures of Electronic Excitations in Raman Scattering in Thin Films of Rhombohedral Graphite
Rhombohedral graphite features peculiar electronic properties, including
persistence of low-energy surface bands of a topological nature. Here, we study
the contribution of electron-hole excitations towards inelastic light
scattering in thin films of rhombohedral graphite. We show that, in contrast to
the featureless electron-hole contribution towards Raman spectrum of graphitic
films with Bernal stacking, the inelastic light scattering accompanied by
electron-hole excitations in crystals with rhombohedral stacking produces
distinct features in the Raman signal which can be used both to identify the
stacking and to determine the number of layers in the film.Comment: 15 pages in preprint format, 4 figures, accepted versio
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