1,505 research outputs found
Observation of inter-Landau-level quantum coherence in semiconductor quantum wells
Using three-pulse four-wave-mixing femtosecond spectroscopy, we excite a
non-radiative coherence between the discrete Landau levels of an undoped
quantum well and study its dynamics. We observe quantum beats that reflect the
time evolution of the coherence between the two lowest Landau level
magnetoexcitons. We interpret our observations using a many-body theory and
find that the inter Landau level coherence decays with a new time constant,
substantially longer than the corresponding interband magnetoexciton dephasing
times. Our results indicate a new intraband excitation dynamics that cannot be
described in terms of uncorrelated interband excitations.Comment: 5 pages, 5 figures, to appear in Phys. Rev. B Rapid Communication
Ultrafast dynamics of coherences in the quantum Hall system
Using three-pulse four-wave-mixing optical spectroscopy, we study the
ultrafast dynamics of the quantum Hall system. We observe striking differences
as compared to an undoped system, where the 2D electron gas is absent. In
particular, we observe a large off-resonant signal with strong oscillations.
Using a microscopic theory, we show that these are due to many-particle
coherences created by interactions between photoexcited carriers and collective
excitations of the 2D electron gas. We extract quantitative information about
the dephasing and interference of these coherences.Comment: 4 pages, 4 figures, to be published in Phys. Rev. Let
Perhitungan Lendutan Pondasi Telapak Dengan Metode Elemen Hingga
Bangunan teknik sipil seperti gedung, jalan dan jembatan bertumpu pada lapisan tanah. Dalam
pelaksanaan pembangunan sering kali tanah tersebut tidak memenuhi kriteria kekuatan untuk memikul
beban dari struktur di atasnya, sehingga diperlukan suatu pemecahan dalam masalah tersebut. Pondasi
memikul beban yang di salurkan oleh kolom sebelum diteruskan ke tanah. Salah satu parameter yang
perlu diperhatikan dalam suatu desain pondasi adalah lendutan. Dalam tulisan ini, lendutan pondasi
telapak dihitung dengan menggunakan metode elemen hingga. Pondasi diasumsikan sebagai struktur
yang rigid dan berada di atas tumpuan elastis/pegas sebagai pengganti pengaruh modulus reaksi tanah.
Desain pondasi pelat dimodelkan sebagai persamaan matrik dari perilaku pelat tipis yang dimodifikasi
terletak di atas tanah. Studi kasus dilakukan untuk mendapatkan lendutan pada tiap-tiap titik nodal.
Dalam metode elemen hingga, pondasi telapak dimodelkan sebagai pelat lentur. Hasil lendutan
maksimum dengan perhitungan manual dan numerik dengan menggunakan software SAP2000.
Perbedaan hasil lendutan maksimum dari kedua metode ini diperoleh sebesar 0.28 %
Rir para refletir : um pedacinho do mundo de Luis Fernando Veríssimo (Caderno de leitura)
Recurso pedagógico desenvolvido como parte da dissertação: SANTANA, Catiana Santos Correia. Crônica de humor : objeto de ensino-aprendizagem na perspectiva do interacinismo sociodiscursivo. 2016. 180 f. Dissertação (Mestrado Profissional em Letras) - Universidade Federal de Sergipe, Itabaiana, SE, 2016.Itabaiana, S
The benefit of urban green area in Kota Kinabalu, Sabah
The city of Kota Kinabalu features several urban green areas, which become the focal points for the urban inhabitants. This study was conducted to determine the benefits and public perceptions that encourage them to visit the local urban green area. The convenience sampling method was used, in which questionnaires were distributed to 101 respondents of the local park visitors. The present finding revealed that most of the respondents strongly agreed that the urban greens help to improve the physical well-being of the urban dwellers (Mean score, µ=4.27), regulate the urban temperature during sunny days (µ=4.20), encourage people to spend more time on outdoor activities in nature (µ=4.14), help to remove air pollutants (µ=4.09), control the amount of water on the ground surface during the rainy season (µ=4.06), reduce stress, anxiety, and depression (µ=4.04), prevent the occurrence of a flash flood (µ=3.98), and promote social interactions among people (µ=3.81). The correlation between the respondents’ education and the mean benefits of urban green areas in Kota Kinabalu was significant (p<0.05). In conclusion, the public perception of the benefits of urban green areas is generally positive, and they also exhibit a high understanding of its importance towards urban dwellers
Prospective association of occupational and leisure-time physical activity with orthostatic blood pressure changes in older adults
\ua9 2023, The Author(s).Orthostatic hypotension (OH) is common in older people. We examined the influence of self-reported occupational-related physical activity (PA) and leisure-time physical exercise (PE) on orthostatic response in a sample of older people over a 2 year period. Supine and orthostatic systolic blood pressure (sBP), diastolic blood pressure (dBP), and mean blood pressure (mBP) were assessed in response to Active Stand (AS) test in 205 older subjects (> 60 years old) at baseline and 2-year follow-up. OH was found in 24 subjects (11.71%) at baseline and 20 subjects (9.76%) after 2 years, with a significant degree of variability in the occurrence of OH after 2 years. Twenty-two subjects who had OH at baseline were free of it after 2 years, two subjects had persistent OH at baseline and after 2 years. After 2 years, adults with occupational PA showed no significant decrease of blood pressure in response to AS test, while lack of undertaking an occupation-related PA was significantly related with a greater decrease in sBP and mBP in response to AS testing in the 1st min. Occupation-related PA and leisure-time-related PE were related to an increase in the response of BP on AS in change between baseline and after 2 years. High between-subjects variance in OH over 2 years was noted. Occupations that involved continuous physical activity and leisure-time physical exercise in middle age were both protective for BP decline on orthostatic stress test within 2 years
Regularity Properties and Pathologies of Position-Space Renormalization-Group Transformations
We reconsider the conceptual foundations of the renormalization-group (RG)
formalism, and prove some rigorous theorems on the regularity properties and
possible pathologies of the RG map. Regarding regularity, we show that the RG
map, defined on a suitable space of interactions (= formal Hamiltonians), is
always single-valued and Lipschitz continuous on its domain of definition. This
rules out a recently proposed scenario for the RG description of first-order
phase transitions. On the pathological side, we make rigorous some arguments of
Griffiths, Pearce and Israel, and prove in several cases that the renormalized
measure is not a Gibbs measure for any reasonable interaction. This means that
the RG map is ill-defined, and that the conventional RG description of
first-order phase transitions is not universally valid. For decimation or
Kadanoff transformations applied to the Ising model in dimension ,
these pathologies occur in a full neighborhood of the low-temperature part of the first-order
phase-transition surface. For block-averaging transformations applied to the
Ising model in dimension , the pathologies occur at low temperatures
for arbitrary magnetic-field strength. Pathologies may also occur in the
critical region for Ising models in dimension . We discuss in detail
the distinction between Gibbsian and non-Gibbsian measures, and give a rather
complete catalogue of the known examples. Finally, we discuss the heuristic and
numerical evidence on RG pathologies in the light of our rigorous theorems.Comment: 273 pages including 14 figures, Postscript, See also
ftp.scri.fsu.edu:hep-lat/papers/9210/9210032.ps.
Evaluating the GeoSnap 13-m Cut-Off HgCdTe Detector for mid-IR ground-based astronomy
New mid-infrared HgCdTe (MCT) detector arrays developed in collaboration with
Teledyne Imaging Sensors (TIS) have paved the way for improved 10-m
sensors for space- and ground-based observatories. Building on the successful
development of longwave HAWAII-2RGs for space missions such as NEO Surveyor, we
characterize the first 13-m GeoSnap detector manufactured to overcome the
challenges of high background rates inherent in ground-based mid-IR astronomy.
This test device merges the longwave HgCdTe photosensitive material with
Teledyne's 2048x2048 GeoSnap-18 (18-m pixel) focal plane module, which is
equipped with a capacitive transimpedance amplifier (CTIA) readout circuit
paired with an onboard 14-bit analog-to-digital converter (ADC). The final
assembly yields a mid-IR detector with high QE, fast readout (>85 Hz), large
well depth (>1.2 million electrons), and linear readout.
Longwave GeoSnap arrays would ideally be deployed on existing ground-based
telescopes as well as the next generation of extremely large telescopes. While
employing advanced adaptive optics (AO) along with state-of-the-art diffraction
suppression techniques, instruments utilizing these detectors could attain
background- and diffraction-limited imaging at inner working angles <10
, providing improved contrast-limited performance compared to JWST
MIRI while operating at comparable wavelengths. We describe the performance
characteristics of the 13-m GeoSnap array operating between 38-45K,
including quantum efficiency, well depth, linearity, gain, dark current, and
frequency-dependent (1/f) noise profile.Comment: 17 pages, 17 figures. Accepted for publication in special addition of
Astronomische Nachrichten / Astronomical Notes as a contribution to SDW202
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Convergence of measures on compactifications of locally symmetric spaces
We conjecture that the set of homogeneous probability measures on the maximal Satake compactification of an arithmetic locally symmetric space S=Γ∖G/K is compact. More precisely, given a sequence of homogeneous probability measures on S, we expect that any weak limit is homogeneous with support contained in precisely one of the boundary components (including S itself). We introduce several tools to study this conjecture and we prove it in a number of cases, including when G=SL3(R) and Γ=SL3(Z)
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