17,317 research outputs found
Cryogenic loss monitors with FPGA TDC signal processing
Radiation hard helium gas ionization chambers capable of operating in vacuum
at temperatures ranging from 5K to 350K have been designed, fabricated and
tested and will be used inside the cryostats at Fermilab's Superconducting
Radiofrequency beam test facility. The chamber vessels are made of stainless
steel and all materials used including seals are known to be radiation hard and
suitable for operation at 5K. The chambers are designed to measure radiation up
to 30 kRad/hr with sensitivity of approximately 1.9 pA/(Rad/hr). The signal
current is measured with a recycling integrator current-to-frequency converter
to achieve a required measurement capability for low current and a wide dynamic
range. A novel scheme of using an FPGA-based time-to-digital converter (TDC) to
measure time intervals between pulses output from the recycling integrator is
employed to ensure a fast beam loss response along with a current measurement
resolution better than 10-bit. This paper will describe the results obtained
and highlight the processing techniques used.Comment: 7 pp. 2nd International Conference on Technology and Instrumentation
in Particle Physics 2011: TIPP 2011. 9-14 Jun 2011. Chicago, Illinoi
Quark Potentials in the Higgs Phase of Large N Supersymmetric Yang-Mills Theories
We compute, in the large N limit, the quark potential for
supersymmetric SU(N) Yang-Mills theory broken to . At
short distances the quarks see only the unbroken gauge symmetry and have an
attractive potential that falls off as 1/L. At longer distances the interquark
interaction is sensitive to the symmetry breaking, and other QCD states appear.
These states correspond to combinations of the quark-antiquark pair with some
number of W-particles. If there is one or more W-particles then this state is
unstable because of the coulomb interaction between the W-particles and between
the W's and the quarks. As L is decreased the W-particles delocalize and these
coulomb branches merge onto a branch with a linear potential. The quarks on
this branch see the unbroken gauge group, but the flux tube is unstable to the
production of W-particles.Comment: 23 pages, 7 figures, harvmac (b
Investigating the BPS Spectrum of Non-Critical E_n Strings
We use the effective action of the non-critical strings to study its
BPS spectrum for . We show how to introduce mass parameters, or
Wilson lines, into the effective action, and then perform the appropriate
asymptotic expansions that yield the BPS spectrum. The result is the
character expansion of the spectrum, and is equivalent to performing the mirror
map on a Calabi-Yau with up to nine K\"ahler moduli. This enables a much more
detailed examination of the structure of the theory, and provides
extensive checks on the effective action description of the non-critical
string. We extract some universal ( independent) information concerning
the degeneracies of BPS excitations.Comment: 50 pages, harvmac (b
Auger electron spectroscopy, secondary ion mass spectroscopy and optical characterization of a-C-H and BN films
The amorphous dielectrics a-C:H and BN were deposited on III-V semiconductors. Optical band gaps as high as 3 eV were measured for a-C:H generated by C4H10 plasmas; a comparison was made with bad gaps obtained from films prepared by CH4 glow discharges. The ion beam deposited BN films exhibited amorphous behavior with band gaps on the order of 5 eV. Film compositions were studied by Auger electron spectroscopy (AES), x-ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS). The optical properties were characterized by ellipsometry, UV/VIS absorption, and IR reflection and transmission. Etching rates of a-C:H subjected to O2 dicharges were determined
Uniaxial and biaxial soft deformations of nematic elastomers
We give a geometric interpretation of the soft elastic deformation modes of
nematic elastomers, with explicit examples, for both uniaxial and biaxial
nematic order. We show the importance of body rotations in this non-classical
elasticity and how the invariance under rotations of the reference and target
states gives soft elasticity (the Golubovic and Lubensky theorem). The role of
rotations makes the Polar Decomposition Theorem vital for decomposing general
deformations into body rotations and symmetric strains. The role of the square
roots of tensors is discussed in this context and that of finding explicit
forms for soft deformations (the approach of Olmsted).Comment: 10 pages, 10 figures, RevTex, AmsTe
Ellipsometric and optical study of some uncommon insulator films on 3-5 semiconductors
Optical properties of three types of insulating films that show promise in potential applications in the 3-4 semiconductor technology were evaluated, namely a-C:H, BN and CaF2. The plasma deposited a-C:H shows an amorphous behavior with optical energy gaps of approximately 2 to 2.4 eV. These a-C:H films have higher density and/or hardness, higher refractive index and lower optical energy gaps with increasing energy of the particles in the plasma, while the density of states remains unchanged. These results are in agreement, and give a fine-tuned positive confirmation to an existing conjecture on the nature of a-C:H films (1). Ion beam deposited BN films show amorphous behavior with energy gap of 5 eV. These films are nonstoichiometric (B/N approximately 2) and have refractive index, density and/or hardness which are dependent on the deposition conditions. The epitaxially grown CaF2 on GaAs films have optical parameters equal to bulk, but evidence of damage was found in the GaAs at the interface
Friction force microscopy : a simple technique for identifying graphene on rough substrates and mapping the orientation of graphene grains on copper
At a single atom thick, it is challenging to distinguish graphene from its substrate using conventional techniques. In this paper we show that friction force microscopy (FFM) is a simple and quick technique for identifying graphene on a range of samples, from growth substrates to rough insulators. We show that FFM is particularly effective for characterizing graphene grown on copper where it can correlate the graphene growth to the three-dimensional surface topography. Atomic lattice stick–slip friction is readily resolved and enables the crystallographic orientation of the graphene to be mapped nondestructively, reproducibly and at high resolution. We expect FFM to be similarly effective for studying graphene growth on other metal/locally crystalline substrates, including SiC, and for studying growth of other two-dimensional materials such as molybdenum disulfide and hexagonal boron nitride
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