2,062 research outputs found
Collapse/Flattening of Nucleonic Bags in Ultra-Strong Magnetic Field
It is shown explicitly using MIT bag model that in presence of ultra-strong
magnetic fields, a nucleon either flattens or collapses in the direction
transverse to the external magnetic field in the classical or quantum
mechanical picture respectively. Which gives rise to some kind of mechanical
instability. Alternatively, it is argued that the bag model of confinement may
not be applicable in this strange situation.Comment: 8 pages, REVTEX, 3 figures .eps files (included
Thermonuclear burst physics with RXTE
Recently we have made measurements of thermonuclear burst energetics and
recurrence times which are unprecedented in their precision, largely thanks to
the sensitivity of the Rossi X-ray Timing Explorer. In the "Clocked Burster",
GS 1826-24, hydrogen burns during the burst via the rapid-proton (rp) process,
which has received particular attention in recent years through theoretical and
modelling studies. The burst energies and the measured variation of alpha (the
ratio of persistent to burst flux) with accretion rate strongly suggests solar
metallicity in the neutron star atmosphere, although this is not consistent
with the corresponding variation of the recurrence time. Possible explanations
include extra heating between the bursts, or a change in the fraction of the
neutron star over which accretion takes place. I also present results from 4U
1746-37, which exhibits regular burst trains which are interrupted by "out of
phase" bursts.Comment: 4 pages, 2 figures, AIP conference proceedings format. To appear in
the proceedings of the "X-ray Timing 2003: Rossi and Beyond" meeting held in
Cambridge, MA, November, 200
Equatorial Spread F structures and associated airglow intensity variations observed over Gadanki
Co-ordinated campaigns have been conducted from Gadanki (13.5° N, 79.2° E, dip lat 6.4° N) by operating simultaneously the Indian MST radar in ionospheric coherent backscatter mode and by monitoring thermosphere airglow line emissions (630.0 nm and 777.4 nm) using a narrow band multi-wavelength scanning photometer during January-March for the past five years (2003–2007) and also during April 2006, as a special campaign. Simultaneous radar and optical observations reveal optical signatures corresponding to a variety of equatorial spread F (ESF) structures. The optical signatures corresponding to ESF structures with wave-like bottomside modulations with plasma plumes, confined bottomside flat and wavelike structures, vertically extended plume structure in the absence of bottomside structure apart from the classical plasma depletions and enhancements are obtained during these campaigns. The plasma depletions and enhancements were identified using optical measurements. In addition, estimations of zonal wavelength of the bottomside structures and the inference of shears in the zonal plasma drift in the presence of confined structures, were carried out using bi-directional airglow measurements. Furthermore, it is found that the vertical columnar intensity of OI 630.0 nm airglow exceeded the slanted columnar intensity in the presence of large bottomside structure. The need for the appropriate physical mechanisms for some of the ESF structures and their characterizations with optical observations are discussed
Purification of Mixed State with Closed Timelike Curve is not Possible
In ordinary quantum theory any mixed state can be purified in an enlarged
Hilbert space by bringing an ancillary system. The purified state does not
depend on the state of any extraneous system with which the mixed state is
going to interact and on the physical interaction. Here, we prove that it is
not possible to purify a mixed state that traverses a closed time like curve
(CTC) and allowed to interact in a consistent way with a causality-respecting
(CR) quantum system in the same manner. Thus, in general for arbitrary
interactions between CR and CTC systems there is no universal 'Church of the
larger Hilbert space' for mixed states with CTC. This shows that in quantum
theory with CTCs there can exist 'proper' and 'improper' mixtures.Comment: Latex2e, No Figs, 4 + pages, An error corrected, Results unchange
Characterizations of the diurnal shapes of OI 630.0 nm dayglow intensity variations: inferences
International audienceMeasurements of OI 630.0 nm thermospheric dayglow emission by means of the Dayglow Photometer (DGP) at Mt. Abu (24.6° N, 73.7° E, dip lat 19.09° N), a station under the crest of Equatorial Ionization Anomaly (EIA), reveal day-to-day changes in the shapes of the diurnal profiles of dayglow intensity variations. These shapes have been characterized using the magnetometer data from equatorial and low-latitude stations. Substantial changes have been noticed in the shapes of the dayglow intensity variations between 10:00?15:00 IST (Indian Standard Time) during the days when normal and counter electrojet events are present over the equator. It is found that the width (the time span corresponding to 0.8 times the maximum dayglow intensity) of the diurnal profile has a linear relationship with the integrated electrojet strength. Occasional deviation from this linear relationship is attributed to the presence of substantial mean meridional wind
Aerosol light absorption from optical measurements of PTFE membrane filter samples: sensitivity analysis of optical depth measures
Mass absorption cross section (MAC) measurements of
atmospherically relevant aerosols are required to quantify their effect on
Earth's radiative budget. Estimating aerosol light absorption from
transmittance and/or reflectance measurements through filter deposits is an
attractive option because of their ease of deployment in field settings, low cost,
and the ability to revisit previously analyzed samples. These measurements
suffer from artifacts that depend on a given filter measurement system and
aerosol optics. Empirical correction algorithms are available for commercial
instruments equipped with optically thick fiber filters, but optically thin
filter media have not been characterized in detail. Here, we present
empirical relationships between particle light absorption optical depth –
measured using multiwavelength integrated photoacoustic spectrometers – and
filter optical depth measurements for polytetrafluoroethylene (PTFE) membrane
filter samples of carbonaceous aerosols generated from combustion of diverse
biomass fuels and kerosene (surrogate for fossil fuel combustion). Through
radiative transfer modeling, we assessed the suitability of three measures of
filter-based optical depth for robustly describing particulate-phase light
absorption over a range of single scattering albedo (SSA) values:
(1) ODs – a measure of transmission of the fraction of incident
radiation that is not backscattered by the filter system – which utilizes
transmittance and reflectance of the sample side of the filter; (2)Â the
commonly used ODc, which uses transmittance and reflectance of the clean
side of the filter; and (3) ATN or the Beer–Lambert attenuation. Modeling
results were also validated experimentally, with ODs showing the
least variability around the mean in this multidimensional parameter space.
We establish a simple, wavelength-independent formulation for calculating
aerosol MAC and absorption coefficients from measurements of ODs.
We find the ratio between in situ particulate absorption optical depth and
ODs to be inversely proportional to aerosol SSA. Our findings
underscore that ODs is a better optical depth measure than
ODc for applying appropriate correction factors when estimating
particle-phase light absorption from filter-based techniques.</p
Nitrogen Fixation (Acetylene Reduction) Associated with Roots of Winter Wheat and Sorghum in Nebraska
Root segments and root-soil cores (6.5-cm diameter) from fields and nurseries of winter wheat and sorghum were tested for N2 fixation by using the acetylene reduction assay. Wheat samples (~1,200) from 109 sites generally had low or no activity (0 to 3.1 nmol of C2H4 produced per h per g [dry weight] of root segments), even after 24 h of incubation. However, a commercial field of Scout 66, located in western Nebraska, exhibited appreciable activity (290 nmol of C2H4 produced per h per g [dry weight] of root segments). Of 400 sorghum lines and crosses, grain sorghums (i.e., CK-60A, Wheatland A, B517, and NP-16) generally exhibited higher nitrogenase activity than forage sorghums or winter wheats. CK-60A, a male sterile grain sorghum, was sampled at four locations and had the most consistent activity of 24 to 1,100 nmol of C2H4 produced per h per core. The maximum rate extrapolated to 2.5 g of N per hectare per day. Numerous N2-fixing bacterial isolates were obtained from wheat and sorghum roots that exhibited high nitrogenase activity. Most isolates were members of the Enterobacteriacae, i.e., Klebsiella pneumoniae, Enterobacter cloacae, and Erwinia herbicola
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