2,525 research outputs found
An analogue method for the analysis of current carrying semiconductor systems
In an earlier Internal Technical Memorandum (1)
and in subsequent
work(2), it has been demonstrated that a particular kind of resistance
network, in which non-linear elements are associated with each mesh
point, can be made to represent an exact analogue to a non-degenerate
semiconductor system in the equilibrium or quasi-equilibrium state.
The term !exact' in this context implies that the difference equation
which governs the potential distribution in the network becomes identical,
for the limit of vanishing mesh interval, with the differential equation
for the electrostatic potential within the semiconductor system, i.e.
the Shockley-Poisson equation. From this type of analogue network
information concerning the variation of maximum field intensity and of
junction capacitance with applied bias voltages can be obtained for one,
two and three dimensional configurations of p and n type regions of
arbitrary geometry and impurity concentration profiles.
One limitation to the applicability of the analogue technique arises
from the restriction to quasi-equilibrium conditions. This restriction
precludes the investigation of situations in which current flow contributions
to the carrier concentration pattern become significant - for example, in
the case of strongly forward biassed p-n junctions, and of p-i-n junctions
and transistors operating at high injection levels. In the present paper,
the problems involved in an extension of the basic analogue method to the
treatment of non-equilibrium situations are examined, and means for their
solution are discussed. A review of the methods previously described
and an illustration of the nature of their limitations is given in Section
2. This is followed, in Sections 3 to 7, by a detailed treatment of
the case of a current carrying semiconductor system in one dimension
which leads to a theoretically possible realization in terms of resistancenetwork/
analogue computer techniques, which is, however, too complex to. be
considered practical. Section 8 discusses means for the simplification of
the proposed schemes and leads to the description of a relatively simple
system in which a significant reduction in equipment complexity has been
made possible by the adoption of an operating mode based upon an iterative
process of successive approximations. The extension of the technique
to three dimensions is outlined in Section 9
C.V.D. annual report: January, 1967 research project ru27-1 : analogue study of semiconductor device structures
The e::tension of the resistance network analogue method to the study
of a M.O.S.T. structure is described. By means of an iterative technique,
data regarding channel current, field distribution, surface charge and
position of pinch-off point as function of gate and drain voltagen can be
obtained which do not involve the usual 'gradual' channel approximation
Results for a particular device geometry are presented.
A discussion of a digital computer approach to the solution of semiconductor
device current flow problems is included, together with preliminary
results
C.V.D. annual report: November 1965 research project RU27-1 :an analogue method for the determination of potential distributions in semiconductor systems
A general method for the solution of the nonlinear
Shockley-Poisson differential equation which
governs the potential distribution in non-degenerate
semiconductor systems is described which can be applied
to the evaluation of depletion layer widths, carrier
densities and capacitance bias relationships of p-n
junction structures.
The method is based upon the use of a particular
type of resistance network analogue and results obtained
for several one and two dimensional configurations are
discussed
Time domain and frequency domain measurement techniques
The principles underlying two distinct approaches to the measurement
of electrical network characteristics over a wide frequency range are
outlined, together with brief descriptions of currently available test
systems which cover the range 0.1 - 4GHZ.
The two techniques are assessed in terms of their ultimate capabilities
with regard to accuracy, speed of measurement and costs
The Electric Double Layer Structure Around Charged Spherical Interfaces
We derive a formally simple approximate analytical solution to the
Poisson-Boltzmann equation for the spherical system via a geometric mapping.
Its regime of applicability in the parameter space of the spherical radius and
the surface potential is determined, and its superiority over the linearized
solution is demonstrated.Comment: 7 pages, 5 figure
Spectroscopic Constraints on the Surface Magnetic Field of the Accreting Neutron Star EXO 0748-676
Gravitationally redshifted absorption lines of Fe XXVI, Fe XXV, and O VIII
were inferred recently in the X-ray spectrum of the bursting neutron star EXO
0748-676. We place an upper limit on the stellar magnetic field based on the
iron lines. The oxygen absorption feature shows a multiple component profile
that is consistent with Zeeman splitting in a magnetic field of ~(1-2)x10^9
gauss, and for which the corresponding Zeeman components of the iron lines are
expected to be blended together. In other systems, a field strength >5x10^{10}
gauss could induce a blueshift of the line centroids that would counteract
gravitational redshift and complicate the derivation of constraints on the
equation of state of the neutron star.Comment: 5 pages, submitted to Phys. Rev. Let
Best-Bet Astrophysical Neutrino Sources
Likely astrophysical sources of detectable high-energy (>> TeV) neutrinos are
considered. Based on gamma-ray emission properties, the most probable sources
of neutrinos are argued to be GRBs, blazars, microquasars, and supernova
remnants. Diffuse neutrino sources are also briefly considered.Comment: 6 pages, 2 figures, in Proc. of TeV-Particle Astrophysics II,
Madison, WI, 28-31 Aug, 200
Observing GRBs with EXIST
We describe the Energetic X-ray Imaging Survey Telescope EXIST, designed to carry out a sensitive all-sky survey in the 10 keV – 600 keV band. The primary goal of EXIST is to find black holes in the local and distant universe. EXIST also traces cosmic star formation via gamma-ray bursts and gamma-ray lines from radioactive elements ejected by supernovae and novae
Complications After Systematic, Random and Image-guided Prostate Biopsy
CONTEXT: Prostate biopsy (PB) represents the gold standard method to confirm the presence of cancer. In addition to traditional random or systematic approaches, a magnetic resonance imaging (MRI)-guided technique has been introduced recently. OBJECTIVE: To perform a systematic review of complications after transrectal ultrasound (TRUS)-guided, transperineal, and MRI-guided PB. EVIDENCE ACQUISITION: We performed a systematic literature search of Web of Science, Embase, and Scopus databases up to October 2015, according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement. Complications and mortality following random, systematic, and image-guided PBs were reviewed. Eighty-five references were included. EVIDENCE SYNTHESIS: The most frequent complication after PB was minor and self-limiting bleeding (hematuria and hematospermia), regardless of the biopsy approach. Occurrence of rectal bleeding was comparable for traditional TRUS-guided and image-guided PBs. Almost 25% of patients experienced lower urinary tract symptoms, but only a few had urinary retention, with higher rates after a transperineal approach. Temporary erectile dysfunction was not negligible, with a return to baseline after 1-6 mo. The incidence of infective complications is increasing, with higher rates among men with medical comorbidities and older age. Transperineal and in-bore MRI-targeted biopsy may reduce the risk of severe infectious complications. Mortality after PB is uncommon, regardless of biopsy technique. CONCLUSIONS: Complications after PB are frequent but often self-limiting. The incidence of hospitalization due to severe infections is continuously increasing. The patient's general health status, risk factors, and likelihood of antimicrobial resistance should be carefully appraised before scheduling a PB. PATIENT SUMMARY: We reviewed the variety and incidence of complications after prostate biopsy. Even if frequent, complications seldom represent a problem for the patient. The most troublesome complications are infections. To minimize this risk, the patient's medical condition should be carefully evaluated before biopsy
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