1,484 research outputs found
A Photoelectric Seed Counter
Small scale yield studies, germination tests, controlled
plantings, and packaging often require the counting of
large numbers of seeds. The system described in this
paper uses a photosensitive detector and a vacuum pickup
to count individual seeds and gives a direct digital readout.
The count rate is limited only by how quickly the
seeds can be fed through the counting tube without clogging
it or having them touch each other. This greatly
speeds seed counting, eliminates operator error, and reduces
operator fatigue.
With the addition of a relatively simple predetermining
circuit, a fixed number of seeds may be counted
and a control function can be exercised. This capability
is immediately applicable to packaging or repetitious
batching of seeds. Zero error for any given number of
seeds is attainable if the seeds are fed through the count
tube carefully because of the completely digital nature
of the circuit
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Top quark pair production cross section in the lepton+jets channel using b-tagging at D0
The top quark pair production cross section measurement in the lepton+jets channel with b-tagging algorithm is described. About 900 pb{sup -1} data collected by the D0 detector at the Fermilab Tevatron are used for this analysis. In this thesis, event selection, background estimation, and cross section calculation are discussed in detail. In addition, calibration of the Luminosity Monitor readout electronics and a new b-tagging algorithm, the SLTNN tagger, are also discussed in this thesis
Photoelectric Tachometer for Precise Centrifuge Speed Determination
Certain chemical and physical investigations such as the
mechanical analysis of soils by centrifugation require that the
speed of rotation of the centrifuge be precisely determined. For
a cost of approximately $40.00, when used with instrumentation
normally available in research laboratories, the system outlined
provides a vivid, unambiguous indication of the speed of rotation,
the accuracy of which is limited only by the frequency
standard used
A Two-Channel Electrical Counter
Many studies require that the magnitude of 2 variables
be determined simultaneously. Usually this is done by an
operator using 2 hand-operated mechanical reciprocating
counters. The operator records one variable on one counter
and the second on the other. Our specific problem was to
determine pollinator densities in field plots. The operators
counted a fixed number of flowers and recorded the number
of pollinators on these flowers.
A number of problems arise from the use of these devices.
The reciprocating counters are hard to use, resulting
in manual fatigue, and are infamous for missing counts,
particularly when they become worn. The operator must
have both hands full all the time he is making the count.
If the operator must do something else with his hands,
he must store the counters where they will not become lost
or interchanged
How the quark self-energy affects the color-superconducting gap
We consider color superconductivity with two flavors of massless quarks which
form Cooper pairs with total spin zero. We solve the gap equation for the
color-superconducting gap parameter to subleading order in the QCD coupling
constant at zero temperature. At this order in , there is also a
previously neglected contribution from the real part of the quark self-energy
to the gap equation. Including this contribution leads to a reduction of the
color-superconducting gap parameter \f_0 by a factor b_0'=\exp \big[ -(\p
^2+4)/8 \big]\simeq 0.177. On the other hand, the BCS relation T_c\simeq
0.57\f_0 between \f_0 and the transition temperature is shown to
remain valid after taking into account corrections from the quark self-energy.
The resulting value for confirms a result obtained previously with a
different method.Comment: Revtex, 8 pages, no figur
(Anti-)self-dual homogeneous vacuum gluon field as an origin of confinement and symmetry breaking in QCD
It is shown that an (anti-)self-dual homogeneous vacuum gluon field appears
in a natural way within the problem of calculation of the QCD partition
function in the form of Euclidean functional integral with periodic boundary
conditions. There is no violation of cluster property within this formulation,
nor are parity, color and rotational symmetries broken explicitly. The massless
limit of the product of the quark masses and condensates, , is calculated to all loop orders. This quantity
does not vanish and is proportional to the gluon condensate appearing due to
the nonzero strength of the vacuum gluon field. We conclude that the gluon
condensate can be considered as an order parameter both for confinement and
chiral symmetry breaking.Comment: 16 pages, LaTe
Multiplicative renormalizability and quark propagator
The renormalized Dyson-Schwinger equation for the quark propagator is
studied, in Landau gauge, in a novel truncation which preserves multiplicative
renormalizability. The renormalization constants are formally eliminated from
the integral equations, and the running coupling explicitly enters the kernels
of the new equations. To construct a truncation which preserves multiplicative
renormalizability, and reproduces the correct leading order perturbative
behavior, non-trivial cancellations involving the full quark-gluon vertex are
assumed in the quark self-energy loop. A model for the running coupling is
introduced, with infrared fixed point in agreement with previous
Dyson-Schwinger studies of the gauge sector, and with correct logarithmic tail.
Dynamical chiral symmetry breaking is investigated, and the generated quark
mass is of the order of the extension of the infrared plateau of the coupling,
and about three times larger than in the Abelian approximation, which violates
multiplicative renormalizability. The generated scale is of the right size for
hadronic phenomenology, without requiring an infrared enhancement of the
running coupling.Comment: 17 pages; minor corrections, comparison to lattice results added;
accepted for publication in Phys. Rev.
Effects of dimensionality and anisotropy on the Holstein polaron
We apply weak-coupling perturbation theory and strong-coupling perturbation
theory to the Holstein molecular crystal model in order to elucidate the
effects of anisotropy on polaron properties in D dimensions. The ground state
energy is considered as a primary criterion through which to study the effects
of anisotropy on the self-trapping transition, the self-trapping line
associated with this transition, and the adiabatic critical point. The effects
of dimensionality and anisotropy on electron-phonon correlations and polaronic
mass enhancement are studied, with particular attention given to the polaron
radius and the characteristics of quasi-1D and quasi-2D structures.
Perturbative results are confirmed by selected comparisons with variational
calculations and quantum Monte Carlo data
Antiflow of kaons in relativistic heavy ion collisions
We compare relativistic transport model calculations to recent data on the
sideward flow of neutral strange K^0_s mesons for Au+Au collisions at 6 AGeV. A
soft nuclear equation of state is found to describe very well the positive
proton flow data measured in the same experiment. In the absence of kaon
potential, the K^0 flow pattern is similar to that of protons. The kaon flow
becomes negative if a repulsive kaon potential determined from the impulse
approximation is introduced. However, this potential underestimates the data
which exhibits larger antiflow. An excellent agreement with the data is
obtained when a relativistic scalar-vector kaon potential, that has stronger
density dependence, is used. We further find that the transverse momentum
dependence of directed and elliptic flow is quite sensitive to the kaon
potential in dense matter.Comment: 5 pages, Revtex, 4 figure
Polaron Effective Mass, Band Distortion, and Self-Trapping in the Holstein Molecular Crystal Model
We present polaron effective masses and selected polaron band structures of
the Holstein molecular crystal model in 1-D as computed by the Global-Local
variational method over a wide range of parameters. These results are augmented
and supported by leading orders of both weak- and strong-coupling perturbation
theory. The description of the polaron effective mass and polaron band
distortion that emerges from this work is comprehensive, spanning weak,
intermediate, and strong electron-phonon coupling, and non-adiabatic, weakly
adiabatic, and strongly adiabatic regimes. Using the effective mass as the
primary criterion, the self-trapping transition is precisely defined and
located. Using related band-shape criteria at the Brillouin zone edge, the
onset of band narrowing is also precisely defined and located. These two lines
divide the polaron parameter space into three regimes of distinct polaron
structure, essentially constituting a polaron phase diagram. Though the
self-trapping transition is thusly shown to be a broad and smooth phenomenon at
finite parameter values, consistency with notion of self-trapping as a critical
phenomenon in the adiabatic limit is demonstrated. Generalizations to higher
dimensions are considered, and resolutions of apparent conflicts with
well-known expectations of adiabatic theory are suggested.Comment: 28 pages, 15 figure
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