9,299 research outputs found
Boosted Higgs in vector-boson associated production at 14 TeV
The production of the Standard Model Higgs boson in association with a vector
boson, followed by the dominant decay to , is a strong
prospect for confirming and measuring the coupling to -quarks in
collisions at TeV. We present an updated study of the prospects
for this analysis, focussing on the most sensitive highly Lorentz-boosted
region. The evolution of the efficiency and composition of the signal and main
background processes as a function of the transverse momentum of the vector
boson are studied covering the region GeV, comparing both a
conventional dijet and jet substructure selection. The lower transverse
momentum region ( GeV) is identified as the most sensitive region for
the Standard Model search, with higher transverse momentum regions not
improving the statistical sensitivity. For much of the studied region
( GeV), a conventional dijet selection performs as well as the
substructure approach, while for the highest transverse momentum regions ( GeV), which are particularly interesting for Beyond the Standard Model and
high luminosity measurements, the jet substructure techniques are essential.Comment: 13 pages.(Fixed figure layout error
Spin relaxation in corrugated graphene
In graphene, out-of-plane (flexural) vibrations and static ripples imposed by
the substrate relax the electron spin, intrinsically protected by mirror
symmetry. We calculate the relaxation times in different scenarios, accounting
for all the possible spin-phonon couplings allowed by the hexagonal symmetry of
the lattice. Scattering by flexural phonons imposes the ultimate bound to the
spin lifetimes, in the ballpark of hundreds of nano-seconds at room
temperature. This estimate and the behavior as a function of the carrier
concentration are substantially altered by the presence of tensions or the
pinning with the substrate. Static ripples also influence the spin transport in
the diffusive regime, dominated by motional narrowing. We find that the
D'yakonov-Perel' mechanism saturates when the mean free path is comparable to
the correlation length of the heights profile. In this regime, the
spin-relaxation times are exclusively determined by the geometry of the
corrugations. Simple models for typical corrugations lead to lifetimes of the
order of tens of micro-seconds.Comment: 4 + epsilon pages; 3 figure
Applications of TIMS data in agricultural areas and related atmospheric considerations
While much of traditional remote sensing in agricultural research was limited to the visible and reflective infrared, advances in thermal infrared remote sensing technology are adding a dimension to digital image analysis of agricultural areas. The Thermal Infrared Multispectral Scanner (TIMS) an airborne sensor having six bands over the nominal 8.2 to 12.2 m range, offers the ability to calculate land surface emissivities unlike most previous singular broadband sensors. Preliminary findings on the utility of the TIMS for several agricultural applications and related atmospheric considerations are discussed
Combined photo- and electroreflectance of multijunction solar cells enabled by subcell electric coupling
Electric coupling between subcells of a monolithically grown multijunction
solar cell in short circuit allows their simultaneous and independent
characterization by means of photo- and electroreflectance. The photovoltage
generated by selective absorption of the pump beam in a given subcell during
photoreflectance measurements results in reverse biasing the complementary
subunits at the modulation frequency set on the pump illumination. Such voltage
bias modulation acts then as external perturbation on the complementary
subcells. The spectral separation of the different subcell absorption ranges
permits the probe beam to record in a single spectrum the response of the
complete device as a combination of photo- and electroreflectance, thereby
providing access for diagnosis of subcells on an individual basis. This form of
modulation spectroscopy is demonstrated on a GaInP/GaAs tandem solar cell.Comment: 5 pages, 4 figures. This article has been accepted by Appl. Phys.
Lett. After it is published, it will be found at
https://doi.org/10.1063/1.506260
Hybrid Micro-Electro-Mechanical Tunable Filter
While advantages such as good thermal stability and processing-chemical compatibilities exist for common monolithic-integrated micro-electro-mechanically tunable filters (MEM-TF) and MEM-tunable vertical cavity surface emitting lasers (MT-VCSEL), they often require full processing to determine device characteristics. Alternatively, the MEM actuators and the optical parts may be fabricated separately, then subsequently bonded. This hybrid approach potentially increases design flexibility. Since hybrid techniques allow integration of heterogeneous material systems, best of breed compound optoelectronic devices may be customized to enable materials groups to be optimized for tasks they are best suited. Thus, as a first step toward a hybrid (AlxGa1-xAs-polySi) MT-VCSEL, this dissertation reports the design, fabrication, and demonstration of an electrostatically actuated hybrid MEM-TF. A 250x250-µm2, 4.92-µm-thick, Al0.4Ga0.6As-GaAs distributed Bragg reflector was successfully flip-bonded to a polySi piston electrostatic actuator using SU-8 photoresist as bonding adhesive. The device demonstrated 53nm (936.5 - 989.5nm) of resonant wavelength tuning over the actuation voltage range of 0 to 10 V
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