465 research outputs found
How successful were the lunar sampling tools: Implications for sampling Mars
Like the Mars Sample Return endeavor, the Apollo lunar-sample program began with definition of strategy for sample collection and of scientific requirements for sampling hardware design. Several lessons can be illustrated by specific tools. The evolution of drive tubes from narrow 2 cm diameter, thick-walled tubes (used on Apollo 11, 12 and 14) to 4 cm diameter, thin-walled tubes used on Apollo 15, 16, and 17) as an example of the improvements made possible during multiple missions. The original Apollo 11 drive tube was designed to work in fluffy soil; thus, only 50 percent of the relatively dense lunar soil was recovered, and the core was distorted. The final configuration resulted in nearly 100 pct recovery with little distortion. The surface samplers (Contact Soil Sampling Devices) were designed to collect the upper 100 micrometer or the upper 1 mm of soil. It was over 2 years after the mission before these particularly specific samplers were opened because interest in them waned. Both core tubes and surface samplers were difficult to open in the laboratory. The Apollo Lunar Sample Return Containers (ALSRCs) were constructed with one indium and 2 Viton seals. They were closed on the lunar surface. Interior container pressures measured upon return to the laboratory indicate that these seals were not reliable in the lunar environment. Also, choice of indium as a sealing material interfered with siderophile analyses of samples
Efficient Hadronic Operators in Lattice Gauge Theory
We study operators to create hadronic states made of light quarks in quenched
lattice gauge theory. We construct non-local gauge-invariant operators which
provide information about the spatial extent of the ground state and excited
states. The efficiency of the operators is shown by looking at the wave
function of the first excited state, which has a node as a function of the
spatial extent of the operator. This allows one to obtain an uncontaminated
ground state for hadrons.Comment: 18 pages, Latex text, followed by 11 postscript figures in
self-unpacking file. Also available at
ftp://suna.amtp.liv.ac.uk/pub/cmi/wavefn
QCD Effective action at high temperature and small chemical potential
We present a construction of an effective Yang-Mills action for QCD, from the
expansion of the fermionic determinant in terms of powers of the chemical
potential at high temperature, for the case of massless quarks. We analyze this
expansion in the perturbative region and find that it gives extra spurious
information. We propose for the non-perturbative sector a simplified effective
action which, in principle, contains only the relevant information.Comment: 3 pages. To appear in the proceedings of the 7th Conference on Strong
& Electroweak Matter (SEWM06), BNL, May 200
Fitting Correlated Hadron Mass Spectrum Data
We discuss fitting hadronic Green functions versus time to extract mass
values in quenched lattice QCD. These data are themselves strongly correlated
in . With only a limited number of data samples, the method of minimising
correlated is unreliable. We explore several methods of modelling the
correlations among the data set by a few parameters which then give a stable
and sensible fit even if the data sample is small. In particular these models
give a reliable estimate of the goodness of fit.Comment: 14 pages, Latex text, followed by 3 postscript figures in
self-unpacking file. Also available at
ftp://suna.amtp.liv.ac.uk/pub/cmi/corfit
Effects of non-perturbatively improved dynamical fermions in UKQCD simulations
We present results for QCD with 2 degenerate flavours of quark using a
non-perturbatively improved action on a lattice volume of where
the bare gauge coupling and bare dynamical quark mass have been chosen to
maintain a fixed physical lattice spacing and volume (1.71 fm). By comparing
measurements from these matched ensembles, including quenched ones, we find
evidence of dynamical quark effects on the short distance static potential, the
scalar glueball mass and the topological susceptibility. There is little
evidence of effects on the light hadron spectrum over the range of quark masses
studied ().Comment: Lattice 2000 (Spectrum and quark masses), 4 pages, 5 figure
Nucleon and gamma N -> Delta lattice form factors in a constituent quark model
A covariant quark model, based both on the spectator formalism and on vector
meson dominance, and previously calibrated by the physical data, is here
extended to the unphysical region of the lattice data by means of one single
extra adjustable parameter - the constituent quark mass in the chiral limit. We
calculated the Nucleon (N) and the gamma N -> Delta form factors in the
universe of values for that parameter described by quenched lattice QCD. A
qualitative description of the Nucleon and gamma N -> Delta form factors
lattice data is achieved for light pions.Comment: To appear in J.Phys.
Where is the chiral critical point in 3-flavor QCD?
We determine the location of the second order endpoint of the line of first
order chiral phase transition in 3-flavor QCD at vanishing chemical potential.
Using Ferrenberg-Swendsen reweighting for two values of the quark mass we
determine the dependence of the transition line on the chemical potential and
locate the chiral critical point. For both quantities we find a significant
quark mass dependence.Comment: 3 pages, Lattice2003(nonzero), one reference exchange
Hadronic decays from the lattice
We discuss strategies to determine hadronic decay couplings from lattice
studies. As an application, we explore the decay of a vector meson to two
pseudoscalar mesons with flavours of sea quark. Although we are working
with quark masses that do not allow a physical decay, we show how the
transition rate can be evaluated from the amplitude for and
from the annihilation component of . We explore the decay
amplitude for two different pion momenta and find consistent results. The
coupling strength we find is in agreement with experiment. We also find
evidence for a shift in the mass caused by mixing with two pion states.Comment: Proc. Latt03 (spectrum), 3 pages, 4 fig
- …