2,681 research outputs found
Absence of molecular mobility on nano-second time scales in amorphous ice phases
High-resolution neutron backscattering techniques are exploited to study the
elastic and quasi-elastic response of the high-density amorphous (HDA), the
low-density amorphous (LDA) and the crystalline ice Ic upon temperature
changes. Within the temperature ranges of their structural stability (HDA at T
> 80 K, LDA at T > 135 K, ice Ic at T < 200 K) the Debye-Waller factors and
mean-square displacements characterise all states as harmonic solids. During
the transformations HDA->LDA (T ~ 100 K), LDA->Ic (T ~ 150K) and the supposed
glass transition with Tg ~ 135 K no relaxation processes can be detected on a
time scale t < 4 ns. It can be concluded from coherent scattering measurements
(D_2O) that LDA starts to recrystallise into ice Ic at T ~ 135 K, i.e. at the
supposed Tg. In the framework of the Debye model of harmonic solids HDA reveals
the highest Debye temperature among the studied ice phases, which is in full
agreement with the lowest Debye level in the generalised density of states
derived from time-of-flight neutron scattering experiments. The elastic results
at low T indicate the presence of an excess of modes in HDA, which do not obey
the Bose statistics
Analisis Trend dan Faktor-faktor yang Mempengaruhi Produksi Gula di Pg. Wringin Anom Kabupaten Situbondo
Pabrik gula merupakan pelaku agribisnis pengolah tanaman tebu dan salah satu sektor yang berperanan penting dalam industri pergulaan di Indonesia. Penelitian ini bertujuan untuk: (1) mengetahui trend luas lahan tebu, produksi dan produktivitas gula di PG. Wringin Anom Kabupaten Situbondo, (2) mengidentifikasi faktor-faktor yang mempengaruhi produksi gula di PG. Wringin Anom Kabupaten Situbondo dan (3) mengukur tingkat efisiensi biaya di PG. Wringin Anom Kabupaten Situbondo. Data dianalisis dengan analisis trend, analisis Cobb-Douglas (uji-t, uji-F, uji Adjusted R2) dan analisis RC-Ratio. Hasil penelitian menunjukkan bahwa: (1) trend luas lahan tebu, produksi dan produktivitas gula di PG. Wringin Anom Kabupaten Situbondo dari tahun 2001-2015 memiliki kecenderunagn meningkat; (2) faktor-faktor yang mempengaruhi produksi gula secara signifikan adalah bobot tebu, rendemen dan tenaga kerja. (3) Penggunaan biaya di PG. Wringin Anom Kabupaten Situbondo menunjukkan tingkat efisien antara tahun 2010-2015 kecuali pada tahun 2010 dan 2013 mengalami inefisiensi biaya
A Comparative Study of the Parker Instability under Three Models of the Galactic Gravity
To examine how non-uniform nature of the Galactic gravity might affect length
and time scales of the Parker instability, we took three models of gravity,
uniform, linear and realistic ones. To make comparisons of the three gravity
models on a common basis, we first fixed the ratio of magnetic pressure to gas
pressure at = 0.25, that of cosmic-ray pressure at = 0.4, and
the rms velocity of interstellar clouds at = 6.4 km s, and then
adjusted parameters of the gravity models in such a way that the resulting
density scale heights for the three models may all have the same value of 160
pc. Performing linear stability analyses onto equilibrium states under the
three models with the typical ISM conditions, we calculate the maximum growth
rate and corresponding length scale for each of the gravity models. Under the
uniform gravity the Parker instability has the growth time of 1.2
years and the length scale of 1.6 kpc for symmetric mode. Under the realistic
gravity it grows in 1.8 years for both symmetric and
antisymmetric modes, and develops density condensations at intervals of 400 pc
for the symmetric mode and 200 pc for the antisymmetric one. A simple change of
the gravity model has thus reduced the growth time by almost an order of
magnitude and its length scale by factors of four to eight. These results
suggest that an onset of the Parker instability in the ISM may not necessarily
be confined to the regions of high and .Comment: Accepted for publication in ApJ, using aaspp4.sty, 18 text pages with
9 figure
Radio and gamma-ray constraints on dark matter annihilation in the Galactic center
We determine upper limits on the dark matter (DM) self-annihilation cross
section for scenarios in which annihilation leads to the production of
electron--positron pairs. In the Galactic centre (GC), relativistic electrons
and positrons produce a radio flux via synchroton emission, and a gamma ray
flux via bremsstrahlung and inverse Compton scattering. On the basis of
archival, interferometric and single-dish radio data, we have determined the
radio spectrum of an elliptical region around the Galactic centre of extent 3
degrees semi-major axis (along the Galactic plane) and 1 degree semi-minor axis
and a second, rectangular region, also centered on the GC, of extent 1.6
degrees x 0.6 degrees. The radio spectra of both regions are non-thermal over
the range of frequencies for which we have data: 74 MHz -- 10 GHz. We also
consider gamma-ray data covering the same region from the EGRET instrument
(about GeV) and from HESS (around TeV). We show how the combination of these
data can be used to place robust constraints on DM annihilation scenarios, in a
way which is relatively insensitive to assumptions about the magnetic field
amplitude in this region. Our results are approximately an order of magnitude
more constraining than existing Galactic centre radio and gamma ray limits. For
a DM mass of m_\chi =10 GeV, and an NFW profile, we find that the
velocity-averaged cross-section must be less than a few times 10^-25 cm^3 s^-1.Comment: 14 pages, 9 figures. Version accepted for publication in PRD.
Reference section updated/extended
Cash Transfers, Early Marriage, and Fertility in Malawi and Zambia
There is increasing interest in the ability of cash transfers to facilitate safe transitions to adulthood in low-income settings; however, evidence from scaled-up government programming demonstrating this potential is scarce. Using two experimental evaluations of unconditional cash transfers targeted to ultra-poor and labor-constrained households over approximately three years in Malawi and Zambia, we examine whether cash transfers delayed early marriage and pregnancy among youth aged 14 to 21 years at baseline. Although we find strong impacts on poverty and schooling, two main pathways hypothesized in the literature, we find limited impacts on safe transition outcomes for both males and females. In addition, despite hypotheses that social norms may constrain potential impacts of cash transfer programs, we show suggestive evidence that pre-program variation in social norms across communities does not significantly affect program impact. We conclude with policy implications and suggestions for future research
The Physical Conditions and Dynamics of the Interstellar Medium in the Nucleus of M83: Observations of CO and CI
This paper presents CI, CO J=4-3, and CO J=3-2 maps of the barred spiral
galaxy M83 taken at the James Clerk Maxwell Telescope. Observations indicate a
double peaked structure which is consistent with gas inflow along the bar
collecting at the inner Lindblad resonance. This structure suggests that
nuclear starbursts can occur even in galaxies where this inflow/collection
occurs, in contrast to previous studies of barred spiral galaxies. However, the
observations also suggest that the double peaked emission may be the result of
a rotating molecular ring oriented nearly perpendicular to the main disk of the
galaxy. The CO J=4-3 data indicate the presence of warm gas in the nucleus that
is not apparent in the lower-J CO observations, which suggests that CO J=1-0
emission may not be a reliable tracer of molecular gas in starburst galaxies.
The twelve CI/CO J=4-3 line ratios in the inner 24'' x 24'' are uniform at the
2 sigma level, which indicates that the CO J=4-3 emission is originating in the
same hot photon-dominated regions as the CI emission. The CO J=4-3/J=3-2 line
ratios vary significantly within the nucleus with the higher line ratios
occurring away from peaks of emission along an arc of active star forming
regions. These high line ratios (>1) likely indicate optically thin gas created
by the high temperatures caused by star forming regions in the nucleus of this
starburst galaxy.Comment: 15 pages with 10 figures. To appear in the August 10 1998 issue of
The Astrophysical Journa
Parker Instability in a Self-Gravitating Magnetized Gas Disk: I. Linear Stability Analysis
To be a formation mechanism of such large-scale structures as giant molecular
clouds (GMCs) and HI superclouds, the classical Parker instability driven by
external gravity has to overcome three major obstacles: The convective motion
accompanying the instability generates thin sheets than large condensations.
The degree of density enhancement achieved by the instability is too low to
make dense interstellar clouds. The time and the length scales of the
instability are significantly longer and larger than the estimated formation
time and the observed mean separation of the GMCs, respectively. This paper
examines whether a replacement of the driving agent from the external to the
self gravity might remove these obstacles by activating the gravitational
instability in the Galactic ISM disk. The self gravity can suppress the
convective motions, and a cooperative action of the Jeans and the Parker
instabilities can remove all the obstacles confronting the classical version of
the Parker instability. The mass and mean separation of the structures
resulting from the odd-parity undular mode solution are shown to agree better
with the HI superclouds than with the GMCs. We briefly discuss how inclusions
of the external gravity and cosmic rays would modify behaviors of the
odd-parity undular mode solution.Comment: 53 pages, 21 figure
NMA CO (J=1-0) Observations of the Halpha/Radio Lobe Galaxy NGC 3079: Gas Dynamics in a Weak Bar Potential and Central Massive Core
within 24 lines with 80 characters) We present ^12CO (1-0) observations in
the central 4.5 kpc (1 arcmin) of the Halpha/Radio lobe galaxy NGC 3079 with
the Nobeyama Millimeter Array. The molecular gas shows four components: a main
disk, spiral arms, a nuclear disk, and a nuclear core. The main disk extends
beyond our spatial coverage. The spiral arms are superimposed on the main disk.
The nuclear disk with about 600 pc radius has an intense concentration of
molecular gas. Its appearance on PV diagrams is indicative of oval motions of
the gas, rather than circular. The nuclear core is more compact than our
resolution. Though it is unresolved, the nuclear core shows a very high
velocity about 200 km/s even at the radius of about 100 pc on the PV diagram.
We propose a model that NGC 3079 contains a weak bar. This model explains the
observed features: the main disk and spiral arms result from gaseous x1-orbits
and associated crowding respectively. The nuclear disk arises from gaseous
x2-orbits. From the appearance of the spiral arms on the PV diagram, the
pattern speed of the bar is estimated to be 55+-10 km/s/kpc. The high velocity
of the nuclear core cannot be explained by our model for a bar. Thus we
attribute it to a central massive core with a dynamical mass of 10^9 Msun
within the central 100 pc. This mass is three orders of magnitude more massive
than that of a central black hole in this galaxy.Comment: 43 pages, 17 figures; ApJ, 573, 105, 200
Molecular Gas Kinematics in Barred Spiral Galaxies
To quantify the effect that bar driven mass inflow can have on the evolution
of a galaxy requires an understanding of the dynamics of the inflowing gas. In
this paper we study the kinematics of the dense molecular gas in a set of seven
barred spiral galaxies to determine which dynamical effects dominate. The
kinematics are derived from observations of the CO J=(1-0) line made with the
Berkeley-Illinois-Maryland Association (BIMA) millimeter array. We compare the
observed kinematics to those predicted by ideal gas hydrodynamic and ballistic
cloud-based models of gas flow in a barred potential. The hydrodynamic model is
in good qualitative agreement with both the current observations of the dense
gas and previous observations of the kinematics of the ionized gas. The
observed kinematics indicate that the gas abruptly changes direction upon
entering the dust lanes to flow directly down the dust lanes along the leading
edge of the bar until the dust lanes approach the nuclear ring. Near the
location where the dust lanes intersect the nuclear ring, we see two velocity
components: a low velocity component, corresponding to gas on circular orbits,
and a higher velocity component, which can be attributed to the fraction of gas
flowing down the bar dust lane which sprays past the contact point toward the
other half of the bar. The ballistic cloud-based model of the ISM is not
consistent with the observed kinematics. The kinematics in the dust lanes
require large velocity gradients which cannot be reproduced by an ISM composed
of ballistic clouds with long mean-free-paths. Therefore, even the dense ISM
responds to hydrodynamic forces.Comment: To be published in the Astrophysical Journal, Nov. 20, 199
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