1,378 research outputs found
ISM gas studies towards the TeV PWN HESS J1825-137 and northern region
HESS J1825-137 is a pulsar wind nebula (PWN) whose TeV emission extends
across ~1 deg. Its large asymmetric shape indicates that its progenitor
supernova interacted with a molecular cloud located in the north of the PWN as
detected by previous CO Galactic survey (e.g Lemiere, Terrier &
Djannati-Ata\"i 2006). Here we provide a detailed picture of the ISM towards
the region north of HESS J1825-137, with the analysis of the dense molecular
gas from our 7mm and 12mm Mopra survey and the more diffuse molecular gas from
the Nanten CO(1-0) and GRS CO(1-0) surveys. Our focus is the possible
association between HESS J1825-137 and the unidentified TeV source to the
north, HESS J1826-130. We report several dense molecular regions whose
kinematic distance matched the dispersion measured distance of the pulsar.
Among them, the dense molecular gas located at (RA,
Dec)=(18.421h,-13.282) shows enhanced turbulence and we suggest that
the velocity structure in this region may be explained by a cloud-cloud
collision scenario. Furthermore, the presence of a H rim may be the
first evidence of the progenitor SNR of the pulsar PSR J1826-1334 as the
distance between the H rim and the TeV source matched with the
predicted SNR radius R~120 pc. From our ISM study, we identify a
few plausible origins of the HESS J1826-130 emission, including the progenitor
SNR of PSR J1826-1334 and the PWN G018.5-0.4 powered by PSR J1826-1256. A
deeper TeV study however, is required to fully identify the origin of this
mysterious TeV source.Comment: 19 figures, 27 pages, accepted by MNRA
Optical properties of potential-inserted quantum wells in the near infrared and Terahertz ranges
We propose an engineering of the optical properties of GaAs/AlGaAs quantum
wells using AlAs and InAs monolayer insertions. A quantitative study of the
effects of the monolayer position and the well thickness on the interband and
intersubband transitions, based on the extended-basis sp3d5s* tight-binding
model, is presented. The effect of insertion on the interband transitions is
compared with existing experimental data. As for intersubband transitions, we
show that in a GaAs/AlGaAs quantum well including two AlAs and one InAs
insertions, a three level {e1 , e2 , e3 } system where the transition energy
e3-e2 is lower and the transition energy e2-e1 larger than the longitudinal
optical phonon energy (36 meV) can be engineered together with a e3-e2
transition energy widely tunable through the TeraHertz range
A neotype designation for the Ascension Frigatebird Fregata aquila (Aves: Fregatidae)
The file attached is the Published/publisherâs pdf version of the article. This is an OpenAccess article
Excitons and high-order optical transitions in individual carbon nanotubes
We examine the excitonic nature of high-lying optical transitions in
single-walled carbon nanotubes by means of Rayleigh scattering spectroscopy. A
careful analysis of the principal transitions of individual semiconducting and
metallic nanotubes reveals that in both cases the lineshape is consistent with
an excitonic model, but not one of free-carriers. For semiconducting species,
side-bands are observed at ~200 meV above the third and fourth optical
transitions. These features are ascribed to exciton-phonon bound states. Such
side-bands are not apparent for metallic nanotubes,as expected from the reduced
strength of excitonic interactions in these systems
Hot electron cooling by acoustic phonons in graphene
We have investigated the energy loss of hot electrons in metallic graphene by
means of GHz noise thermometry at liquid helium temperature. We observe the
electronic temperature T / V at low bias in agreement with the heat diffusion
to the leads described by the Wiedemann-Franz law. We report on
behavior at high bias, which corresponds to a T4 dependence
of the cooling power. This is the signature of a 2D acoustic phonon cooling
mechanism. From a heat equation analysis of the two regimes we extract accurate
values of the electron-acoustic phonon coupling constant in monolayer
graphene. Our measurements point to an important effect of lattice disorder in
the reduction of , not yet considered by theory. Moreover, our study
provides a strong and firm support to the rising field of graphene bolometric
detectors.Comment: 5 figure
Texas General Land Office Parcels: El Paso, Hudspeth, And Reeves Counties, Texas
In June 2015, Natural Resource Group, LLC conducted Phase I cultural resource investigations within eight parcels that are managed by the Texas General Land Office. The tracts are located in El Paso, Hudspeth, and Reeves counties, Texas and the studies are associated with Phase 1 of the Roadrunner Gas Transmission, LLC (Roadrunner) Roadrunner Project. Roadrunner has entered into an operating agreement with ONEOK WesTex Transmission Company, L.L.C. (WesTex), a subsidiary of ONEOK, to construct, operate and maintain an intrastate pipeline in the State of Texas under the jurisdiction of the Texas Railroad Commission. WesTex plans to construct approximately 205 miles of 30-inch diameter natural gas intrastate pipeline that begins in Pecos County, Texas, and extends westward across Reeves, Culberson, Hudspeth, and El Paso counties. Construction will occur in two stages (Phase 1 and Phase 2). Phase 1 consists of two greenfield segments on the eastern and western ends of the proposed route that total approximately 105 miles. The Phase 2 corridor is approximately 100 miles long, and connects the two Phase 1 segments by generally following an existing pipeline corridor.
The studies were authorized under Texas Antiquities Permit #7252 and General Land Office Authorization to Conduct Archeology No. 15-0010. They were conducted within a 300-foot-wide survey corridor and along segments of five proposed access roads.
No previously recorded archaeological sites or historic structures occur within the investigated areas, and no new cultural resources were identified during the field effort. Therefore, we recommend that construction be allowed to proceed as currently planned without further consideration of cultural resources
Efficient dynamical nuclear polarization in quantum dots: Temperature dependence
We investigate in micro-photoluminescence experiments the dynamical nuclear
polarization in individual InGaAs quantum dots. Experiments carried out in an
applied magnetic field of 2T show that the nuclear polarization achieved
through the optical pumping of electron spins is increasing with the sample
temperature between 2K and 55K, reaching a maximum of about 50%. Analysing the
dependence of the Overhauser shift on the spin polarization of the optically
injected electron as a function of temperature enables us to identify the main
reasons for this increase.Comment: 5 pages, 3 figure
Electron spin quantum beats in positively charged quantum dots: nuclear field effects
We have studied the electron spin coherence in an ensemble of positively
charged InAs/GaAs quantum dots. In a transverse magnetic field, we show that
two main contributions must be taken into account to explain the damping of the
circular polarization oscillations. The first one is due to the nuclear field
fluctuations from dot to dot experienced by the electron spin. The second one
is due to the dispersion of the transverse electron Lande g-factor, due to the
inherent inhomogeneity of the system, and leads to a field dependent
contribution to the damping. We have developed a model taking into account both
contributions, which is in good agreement with the experimental data. This
enables us to extract the pure contribution to dephasing due to the nuclei.Comment: 10 pages, 6 figure
Nondissipative Addressing for Time-Division SQUID Multiplexing
International audienceRecent and future astronomical instruments are based on a focal plane mapped by a large array of superconducting bolometers. Cryogenic analog multiplexing readout techniques, based on superconducting quantum interference devices (SQUIDs), are currently developed to achieve the readout of large arrays of this kind of low noise background-limited detectors. To effectively reduce the number of cryogenic wires (particularly, SQUID biasing), line/column addressing is currently used in time-division multiplexing, i.e., same biasing is applied to a few SQUIDs (on a line) of different columns. This technique should dramatically increase power consumption if parallel biasing is applied via resistors to isolate each column; the power budget is particularly limited on this kind of front-end cryogenic readout. A design with one transformer per SQUID is also used to read out SQUID biased in series with no excess of consumption and crosstalk. We propose here a new biasing technique using simple surface-mounted capacitors, which is easier to implement. These capacitors are used to parallel bias SQUIDs without additional Joule effect while minimizing crosstalk. However, capacitors do not allow dc biasing and need a current mean value equal to zero to avoid biasing source saturation. We have then tested square current biasing through capacitors on a commercial SQUID. This measurement shows that capacitors are able to proper bias SQUID and then to perform a nondissipative addressing for time-division SQUID multiplexing
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