984 research outputs found
Contribution of Extragalactic Infrared Sources to CMB Foreground Anisotropy
We estimate the level of confusion to Cosmic Microwave Background anisotropy
measurements caused by extragalactic infrared sources. CMB anisotropy
observations at high resolution and high frequencies are especially sensitive
to this foreground. We use data from the COBE satellite to generate a Galactic
emission spectrum covering mm and sub-mm wavelengths. Using this spectrum as a
template, we predict the microwave emission of the 5319 brightest infrared
galaxies seen by IRAS. We simulate skymaps over the relevant range of
frequencies (30-900 GHz) and instrument resolutions (10'-10 degrees Full Width
Half Max). Analysis of the temperature anisotropy of these skymaps shows that a
reasonable observational window is available for CMB anisotropy measurements.Comment: 14 pages (LaTex source), 3 PostScript figures. Final version, to
appear in ApJLetters May 1. Expanded discussion of systematic error
Insights into the off-state breakdown mechanisms in power GaN HEMTs
We analyze the off-state, three-terminal, lateral breakdown in AlGaN/GaN HEMTs for power switching applications by comparing two-dimensional numerical device simulations with experimental data from device structures with different gate-to-drain spacing and with either undoped or Carbon-doped GaN buffer layer. Our simulations reproduce the different breakdown-voltage dependence on the gate-drain-spacing exhibited by the two types of device and attribute the breakdown to: i) a combination of gate electron injection and source-drain punch-through in the undoped HEMTs; and ii) avalanche generation triggered by gate electron injection in the C-doped HEMTs
Generalized Quasilinear Approximation: Application to Zonal Jets
Quasilinear theory is often utilized to approximate the dynamics of fluids exhibiting significant interactions between mean flows and eddies. We present a generalization of quasilinear theory to include dynamic mode interactions on the large scales. This generalized quasilinear (GQL) approximation is achieved by separating the state variables into large and small zonal scales via a spectral filter rather than by a decomposition into a formal mean and fluctuations. Nonlinear interactions involving only small zonal scales are then removed. The approximation is conservative and allows for scattering of energy between small-scale modes via the large scale (through nonlocal spectral interactions). We evaluate GQL for the paradigmatic problems of the driving of large-scale jets on a spherical surface and on the beta plane and show that it is accurate even for a small number of large-scale modes. As GQL is formally linear in the small zonal scales, it allows for the closure of the system and can be utilized in direct statistical simulation schemes that have proved an attractive alternative to direct numerical simulation for many geophysical and astrophysical problems
High-Resolution Spectroscopy of FUors
High-resolution spectroscopy was obtained of the FUors FU Ori and V1057 Cyg
between 1995 and 2002 with SOFIN at NOT and with HIRES at Keck I. During those
years FU Ori remained about 1 mag. (in B) below its 1938-39 maximum brightness,
but V1057 Cyg (B ~ 10.5 at peak in 1970-71) faded from about 13.5 to 14.9 and
then recovered slightly. Their photospheric spectra resemble a rotating G0 Ib
supergiant, with v_eq sin i = 70 km/s for FU Ori and 55 km/s for V1057 Cyg. As
V1057 Cyg faded, P Cyg structure in Halpha and the IR CaII lines strengthened
and a complex shortward-displaced shell spectrum increased in strength,
disappeared in 1999, and reappeared in 2001. Night-to-night changes in the wind
structure of FU Ori show evidence of sporadic infall. The strength of P Cyg
absorption varied cyclically with a period of 14.8 days, with phase stability
maintained over 3 seasons, and is believed to be the rotation period. The
structure of the photospheric lines also varies cyclically, but with a period
of 3.54 days. A similar variation may be present in V1057 Cyg. As V1057 Cyg has
faded, the emission lines of a pre-existing low-excitation chromosphere have
emerged, so we believe the `line doubling' in V1057 Cyg is produced by these
central emission cores in the absorption lines, not by orbital motion in an
inclined Keplerian disk. No dependence of v_eq sin i on wavelength or
excitation potential was detected in either star, again contrary to expectation
for a self-luminous accretion disk. Nor are critical lines in the near infrared
accounted for by synthetic disk spectra. A rapidly rotating star near the edge
of stability (Larson 1980), can better explain these observations. FUor
eruptions may not be a property of ordinary TTS, but may be confined to a
special subspecies of rapid rotators having powerful quasi-permanent winds.Comment: 41 pages (including 32 figures and 9 tables); ApJ, in press; author
affiliation, figs. 3 and 9 correcte
Estudo cinético de consumo de nitrogênio pelo processo anammox.
A oxidação anaeróbia de amônia (anammox) é um processo biotecnológico. Microrganismos com atividade anammox apresentam alta capacidade de remoção de nitrogênio e baixa produção de lodo, que se reflete em maiores tempos, pois a duplicação celular é alta (> 7 dias) quando comparada a de outros processos prejudicando a partida do processo. Diferentes condições de operação são testadas no intuito de reduzir o tempo de partida do processo e melhorar a eficiência na remoção de nitrogênio. Estudos cinéticos são uma boa ferramenta para avaliar a eficiência de reatores biológicos. O estudo avaliou o comportamento de dois reatores com atividade anammox operando a TRHs de 3,19h e 0,56h mediante cinéticas de consumo de N-NO2- e N-NH3. O estudo cinético foi conduzido durante 2,5 horas em batelada avaliando-se o decaimento de nitrito e nitrogênio amoniacal. O reator com menor TRH (0,56h) obteve velocidade de consumo de 18,4 mgN-NH3.L-1.h-1 e 28,9 mgN-NO2-.L-1.h-1 e eficiência de 64% na remoção de nitrogênio. O reator de TRH (3,19h), obteve a velocidade de consumo de 1,4 mgN-NH3.L-1.h-1 e 2,6 mgN-NO2-.L-1 e eficiência de apenas 11% na remoção de nitrogênio. A partir dos resultados obtidos, observa-se que a redução do TRH em 80% aumentou a atividade do processo em cerca de 90%
Mapping the CMB II: the second flight of the QMAP experiment
We report the results from the second flight of QMAP, an experiment to map
the cosmic microwave background near the North Celestial Pole. We present maps
of the sky at 31 and 42 GHz as well as a measurement of the angular power
spectrum covering the l-range 40-200. Anisotropy is detected at about 20 sigma
and is in agreement with previous results at these angular scales. We also
report details of the data reduction and analysis techniques which were used
for both flights of QMAP.Comment: 4 pages, with 5 figures included. Submitted to ApJL. Window functions
and color figures are available at
http://pupgg.princeton.edu/~cmb/welcome.htm
Modulated patterns in a reduced model of a transitional shear flow
We consider a close relative of plane Couette flow called Waleffe flow in which the fluid is confined between two free-slip walls and the flow driven by a sinusoidal force. We use a reduced model of such flows constructed elsewhere to compute stationary exact coherent structures of Waleffe flow in periodic domains with a large spanwise period. The computations reveal the emergence of stationary states exhibiting strong amplitude and wavelength modulation in the spanwise direction. These modulated states lie on branches exhibiting complex dependence on the Reynolds number but no homoclinic snaking
Star formation in z>1 3CR host galaxies as seen by Herschel
We present Herschel (PACS and SPIRE) far-infrared (FIR) photometry of a
complete sample of z>1 3CR sources, from the Herschel GT project The Herschel
Legacy of distant radio-loud AGN (PI: Barthel). Combining these with existing
Spitzer photometric data, we perform an infrared (IR) spectral energy
distribution (SED) analysis of these landmark objects in extragalactic research
to study the star formation in the hosts of some of the brightest active
galactic nuclei (AGN) known at any epoch. Accounting for the contribution from
an AGN-powered warm dust component to the IR SED, about 40% of our objects
undergo episodes of prodigious, ULIRG-strength star formation, with rates of
hundreds of solar masses per year, coeval with the growth of the central
supermassive black hole. Median SEDs imply that the quasar and radio galaxy
hosts have similar FIR properties, in agreement with the orientation-based
unification for radio-loud AGN. The star-forming properties of the AGN hosts
are similar to those of the general population of equally massive non-AGN
galaxies at comparable redshifts, thus there is no strong evidence of universal
quenching of star formation (negative feedback) within this sample. Massive
galaxies at high redshift may be forming stars prodigiously, regardless of
whether their supermassive black holes are accreting or not.Comment: 30 pages, 13 figures, 4 tables. Accepted for publication in A&
On Semiclassical Limits of String States
We explore the relation between classical and quantum states in both open and
closed (super)strings discussing the relevance of coherent states as a
semiclassical approximation. For the closed string sector a gauge-fixing of the
residual world-sheet rigid translation symmetry of the light-cone gauge is
needed for the construction to be possible. The circular target-space loop
example is worked out explicitly.Comment: 12 page
Metodologia de determinação do pH da temperatura da cama de aviário em tempo real.
Projeto: 03.07.09.049
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