11,631 research outputs found
Benzene formation in the inner regions of protostellar disks
Benzene (c-C6H6) formation in the inner 3 AU of a protostellar disk can be
efficient, resulting in high abundances of benzene in the midplane region. The
formation mechanism is different to that found in interstellar clouds and in
protoplanetary nebulae, and proceeds mainly through the reaction between allene
(C3H4) and its ion. This has implications for PAH formation, in that some
fraction of PAHs seen in the solar system could be native rather than inherited
from the interstellar medium.Comment: 9 pages, 2 colour figures, to be published in the Astrophysical
Journal Letter
Low temperature metallic state induced by electrostatic carrier doping of SrTiO
Transport properties of SrTiO-channel field-effect transistors with
parylene organic gate insulator have been investigated. By applying gate
voltage, the sheet resistance falls below 10 k at low
temperatures, with carrier mobility exceeding 1000 cm/Vs. The temperature
dependence of the sheet resistance taken under constant gate voltage exhibits
metallic behavior (/ 0). Our results demonstrate an insulator to
metal transition in SrTiO driven by electrostatic carrier density control.Comment: 3 pages, 4 figure
On Energy Reduction and Green Networking Enhancement due to In-Network Caching
In-network caching in information centric networking
(ICN) is considered as a promising approach to reducing
energy consumption of an entire network. However, it is also considered as an energy consuming technique. These contradictory claims lead to one research question: Does caching really reduce the energy consumption of the entire network? To answer the question, we formulate an ICN network as an optimization problem with a realistic energy consumption model for an ICN router. By solving the formulation assuming that ICN forwarding software currently under development is used as a forwarding engine of an ICN router, we reveal that in-network
caching alone does not reduce much energy but it enhances a currently developed green networking technique even though the forwarding engine is not fully optimized
On Energy Reduction and Green Networking Enhancement due to In-Network Caching
In-network caching in information centric networking
(ICN) is considered as a promising approach to reducing
energy consumption of an entire network. However, it is also considered as an energy consuming technique. These contradictory claims lead to one research question: Does caching really reduce the energy consumption of the entire network? To answer the question, we formulate an ICN network as an optimization problem with a realistic energy consumption model for an ICN router. By solving the formulation assuming that ICN forwarding software currently under development is used as a forwarding engine of an ICN router, we reveal that in-network
caching alone does not reduce much energy but it enhances a currently developed green networking technique even though the forwarding engine is not fully optimized
CB17: Inferring the dynamical history of a prestellar core with chemo-dynamical models
We present a detailed theoretical study of the isolated Bok globule CB17
(L1389) based on spectral maps of CS, HCO, CO, CS, and
HCO lines. A phenomenological model of prestellar core evolution, a
time-dependent chemical model, and a radiative transfer simulation for
molecular lines are combined to reconstruct the chemical and kinematical
structure of this core. We developed a general criterion that allows to
quantify the difference between observed and simulated spectral maps. By
minimizing this difference, we find that very high and very low values of the
effective sticking probability are not appropriate for the studied
prestellar core. The most probable value for CB17 is 0.3--0.5. The spatial
distribution of the intensities and self-absorption features of optically thick
lines is indicative of UV irradiation of the core. By fitting simultaneously
optically thin and optically thick transitions, we isolate the model that
reproduces all the available spectral maps to a reasonable accuracy. The line
asymmetry pattern in CB17 is reproduced by a combination of infall, rotation,
and turbulent motions with velocities km s, km
s, and km s, respectively. These parameters corresponds
to energy ratios , , and (the rotation
parameters are determined for ). The chemical age of the core is
about 2 Myrs. In particular, this is indicated by the central depletion of CO,
CS, and HCO. Based on the angular momentum value, we argue that the core is
going to fragment, i.e., to form a binary (multiple) star. (abridged)Comment: ApJ, in pres
Detection of Acetylene toward Cepheus A East with Spitzer
The first map of interstellar acetylene (C2H2) has been obtained with the
infrared spectrograph onboard the Spitzer Space Telescope. A spectral line map
of the vibration-rotation band at 13.7 microns carried out toward the
star-forming region Cepheus A East, shows that the C2H2 emission peaks in a few
localized clumps where gas-phase CO2 emission was previously detected with
Spitzer. The distribution of excitation temperatures derived from fits to the
C2H2 line profiles ranges from 50 to 200 K, a range consistent with that
derived for gaseous CO2 suggesting that both molecules probe the same warm gas
component. The C2H2 molecules are excited via radiative pumping by 13.7 microns
continuum photons emanating from the HW2 protostellar region. We derive column
densities ranging from a few x 10^13 to ~ 7 x 10^14 cm^-2, corresponding to
C2H2 abundances of 1 x 10^-9 to 4 x 10^-8 with respect to H2. The spatial
distribution of the C2H2 emission along with a roughly constant N(C2H2)/N(CO2)
strongly suggest an association with shock activity, most likely the result of
the sputtering of acetylene in icy grain mantles.Comment: 11 pages, 5 figures, accepted for publication in ApJ Letter
TMC-1C: an accreting starless core
We have mapped the starless core TMC-1C in a variety of molecular lines with
the IRAM 30m telescope. High density tracers show clear signs of
self-absorption and sub-sonic infall asymmetries are present in N2H+ (1-0) and
DCO+ (2-1) lines. The inward velocity profile in N2H+ (1-0) is extended over a
region of about 7,000 AU in radius around the dust continuum peak, which is the
most extended ``infalling'' region observed in a starless core with this
tracer. The kinetic temperature (~12 K) measured from C17O and C18O suggests
that their emission comes from a shell outside the colder interior traced by
the mm continuum dust. The C18O (2-1) excitation temperature drops from 12 K to
~10 K away from the center. This is consistent with a volume density drop of
the gas traced by the C18O lines, from ~4x10^4 cm^-3 towards the dust peak to
~6x10^3 cm^-3 at a projected distance from the dust peak of 80" (or 11,000 AU).
The column density implied by the gas and dust show similar N2H+ and CO
depletion factors (f_D < 6). This can be explained with a simple scenario in
which: (i) the TMC-1C core is embedded in a relatively dense environment (H2
~10^4 cm^-3), where CO is mostly in the gas phase and the N2H+ abundance had
time to reach equilibrium values; (ii) the surrounding material (rich in CO and
N2H+) is accreting onto the dense core nucleus; (iii) TMC-1C is older than
3x10^5 yr, to account for the observed abundance of N2H+ across the core
(~10^-10 w.r.t. H2); and (iv) the core nucleus is either much younger (~10^4
yr) or ``undepleted'' material from the surrounding envelope has fallen towards
it in the past 10,000 yr.Comment: 29 pages, including 5 tables and 15 figure
Power Consumption Model of NDN-Based Multicore Software Router Based on Detailed Protocol Analysis
Named data networking (NDN) has received considerable attention recently, mainly due to its built-in caching, which is expected to enable widespread and transparent operator-controlled caching. One of the important research challenges is to reduce the amount of power consumed by NDN networks as it has been shown that NDN's name prefix matching and caching are power-hungry. As a first step to achieving power-efficient NDN networks, in this paper, we develop a power consumption model of a multicore software NDN router. By applying this model to analyze how caching reduces power, we report that caching can reduce power consumption of an NDN network if the power consumption of routers is in proportion to their load and the computation of caching is as light as that of forwarding
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