6,074 research outputs found
Survival and Nonescape Probabilities for Resonant and Nonresonant Decay
In this paper we study the time evolution of the decay process for a particle
confined initially in a finite region of space, extending our analysis given
recently (Phys. Rev. Lett. 74, 337 (1995)). For this purpose, we solve exactly
the time-dependent Schroedinger equation for a finite-range potential. We
calculate and compare two quantities: (i) the survival probability S(t), i.e.,
the probability that the particle is in the initial state after a time t; and
(ii) the nonescape probability P(t), i.e., the probability that the particle
remains confined inside the potential region after a time t. We analyze in
detail the resonant and nonresonant decay. In the former case, after a very
short time, S(t) and P(t) decay exponentially, but for very long times they
decay as a power law, albeit with different exponents. For the nonresonant case
we obtain that both quantities differ initially. However, independently of the
resonant and nonresonant character of the initial state we always find a
transition to the ground state of the system which indicates a process of
``loss of memory'' in the decay.Comment: 26 pages, RevTex file, figures available upon request from
[email protected] (To be published in Annals of Physics
Resonance expansions in quantum mechanics
The goal of this contribution is to discuss various resonance expansions that
have been proposed in the literature.Comment: 10 pages and 1 figure; presented at the Istanbul workshop on
pseudo-Hermitian Hamiltonian
Response time of a normal-superconductor hybrid system under the step-like pulse bias
The response of a quantum dot coupled with one normal lead and a
superconductor lead driven by a step-like pulse bias is studied using the
non-equilibrium Green function method. In the linear pulse bias regime, the
responses of the upwards and downwards bias are symmetric. In this regime the
turn-on time and turn-off time are much slower than that of the normal system
due to the Andreev reflection. On the other hand, for the large pulse bias
, the instantaneous current exhibits oscillatory behaviors with the
frequency . The turn on/off times are in (or shorter than)
the scale of , so they are faster for the larger bias . In
addition, the responses for the upwards and downwards bias are asymmetric at
large . The turn-on time is larger than the turn-off time but the
relaxation time \cite{note1} depends only on the coupling strength and
it is much smaller than the turn-on/off times for the large bias .Comment: 8 pages, 4 figures, accepted for publication in Phys. Rev.
Estudio del efecto del tamaño en la estructura cristalina de nanopartículas de CoFe2O4
Se estudió como afecta el tamaño de nanopartículas de ferrita de cobalto en el desorden cristalino por efecto de superficie. Las nanopartículas se obtuvieron por el método de coprecipitación de sales. Para controlar el tamaño realizaron diferentes tratamientos térmicos posteriores a la síntesis. La estructura cristalina y la morfología se evaluaron por medio de Difracción de rayos-X y Microscopía Electrónica de Transmisión de Alta Resolución. Los resultados obtenidos demuestran en forma cuantitativa, cómo la variación en la relación superficie/volumen es responsable de las deformaciones presentes en las nanoestructuras.Fil: Menchaca Nal, Sandra. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de Coordinacion Administrativa Houssay. Instituto de Tecnologia En Polimeros y Nanotecnologia; ArgentinaFil: Londoño Calderon, Cesar Leandro. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de Coordinacion Administrativa Houssay. Instituto de Tecnologia En Polimeros y Nanotecnologia; ArgentinaFil: Pardo Saavedra, D. C.. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Tecnologías y Ciencias de la Ingeniería; ArgentinaFil: Pampillo, L. G.. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Tecnologías y Ciencias de la Ingeniería; ArgentinaFil: Socolovsky, Leandro Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Tecnologías y Ciencias de la Ingeniería; ArgentinaFil: Martinez Garcia, Ricardo. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de Coordinacion Administrativa Houssay. Instituto de Tecnologia En Polimeros y Nanotecnologia; Argentin
A search for substellar members in the Praesepe and sigma Orionis clusters
(Abridged). We have conducted deep photometric searches for substellar
members of the Praesepe (0.5-1 Gyr) and sigma Orionis (3 Myr) star clusters
using the Sloan i' and z' filters, the 3.5-m and the 5-m Hale telescopes on the
Calar Alto and Palomar Observatories, respectively. The total area surveyed was
1177 arcmin^2 (Praesepe) and 1122 arcmin^2 (sigma Orionis) down to 5-sigma
detection limits of i'= 24.5 and z'= 24 mag, corresponding to masses of 50-55
M_Jup (Praesepe) and 6 M_Jup (sigma Orionis). Besides recovering previously
known cluster members reported in the literature, we have identified new
photometric candidates in both clusters whose masses expand the full range
covered by our study. In sigma Orionis, follow-up NIR photometry has allowed us
to confirm the likely cluster membership of three newly discovered
planetary-mass objects. The substellar mass function of sigma Orionis, which is
complete from the star-brown dwarf borderline down to 7 M_Jup, keeps rising
smoothly with a slope of alpha = 0.6^{+0.5}_{-0.1}. Very interestingly, one of
the faintest Praesepe candidates for which we have also obtained follow-up JHK
photometry nicely fits the expected optical and infrared photometric sequence
of the cluster. From its colors, we have estimated its spectral type in the
L4-L6 range. If confirmed as a true Praesepe member, it would become the first
L-type brown dwarf (50-60 M_Jup) identified in an intermediate-age star
cluster. Our derivation of the Praesepe mass function depends strongly on the
cluster age. For the youngest possible ages (500-700 Myr), our results suggest
that there is a deficit of Praesepe brown dwarfs in the central regions of the
cluster, while the similarity between the Praesepe and sigma Orionis mass
functions increases qualitatively for models older than 800 Myr.Comment: Accepted for publication in A&A. Figures 1, 7, and 9-12 are available
in jpeg forma
Cancer Survivors\u27 Self-Efficacy and Spirituality Outcomes Following a Holistic Integrative Intervention
Cancer treatments often negatively impact health-related quality of life (HR-QOL) for cancer survivors (CS), ignoring the multi-dimensional nature of the human experience of cancer and its impact on mental and spiritual domains. A holistic integrative approach was implemented on a heterogenous population of cancer survivors during the COVID epidemic with the goal of improving their overall well-being by looking beyond physical functioning. PURPOSE: To examine the relationship between spirituality and self-efficacy of cancer survivors of all types of cancer following a holistic intervention during the COVID-19 pandemic. METHODS: Subjects were recruited via network partners and self-referral. Subjects were eligible to participate if they were cancer survivors of any type at any stage of cancer treatment; subjects were ineligible to participate if they presented with any absolute contraindications to exercise testing as per ACSM guidelines. For 16 weeks, subjects were asked to participate in three 75-minute sessions of therapeutic yoga-based with loving kindness meditation per week. Psychosocial support text messages were sent daily to subjects based on their motivational state to encourage participation in these health enhancing behaviors. Data was collected through numerous channels including BlueJay Mobile Telehealth medicine application. RESULTS: A total of 29 survivors provided informed consent. The average age of the subjects was 58.9 years, 25 female survivors and 4 male survivors; 11 of the 29 self-reported as Latino/ Hispanic. The 29 subjects were survivors of the following primary cancers: breast cancer (n=21), cervical cancer (n=2), ovarian cancer (n=1), prostate cancer (n=1), sarcoma (n=1), lymphoma (n=1), thyroid cancer (n=1), or leukemia (n=1). There is a positive association between how confident a cancer survivor feels towards performing exercise in various situations and the amount of social support they receive from their family (p\u3c.001) and friends (p\u3c.001). The individual’s confidence to overcome the obstacle to exercise and their level of hope are associated with the support they receive from loved ones. CONCLUSION: The present study suggests that to improve exercise behavior in adult cancer survivors, one should incorporate social support to strengthen barriers self-efficacy to improve outcome expectations. To further understand these associations, longitudinal research is needed and should include more survivors
Irreversible Quantum Mechanics in the Neutral K-System
The neutral Kaon system is used to test the quantum theory of resonance
scattering and decay phenomena. The two dimensional Lee-Oehme-Yang theory with
complex Hamiltonian is obtained by truncating the complex basis vector
expansion of the exact theory in Rigged Hilbert space. This can be done for K_1
and K_2 as well as for K_S and K_L, depending upon whether one chooses the
(self-adjoint, semi-bounded) Hamiltonian as commuting or non-commuting with CP.
As an unexpected curiosity one can show that the exact theory (without
truncation) predicts long-time 2 pion decays of the neutral Kaon system even if
the Hamiltonian conserves CP.Comment: 36 pages, 1 PostScript figure include
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