11,679 research outputs found
Letter to the editor. NAA and JFK: Can revisionism take us home?
Occasionally during the course of the human learning experience we are faced
with an anomaly. An aberration of sorts, which try as we might, defies
appropriate classification. The recent paper by Spiegelman et al.--Chemical and
forensic analysis of JFK assassination bullet lots: Is a second shooter
possible?--is one such aberration. It is riddled with both misconceptions and
errors of fact. Purporting to cast doubt on the NAA (neutron activation
analysis) work conducted by Dr. Vincent Guinn in the investigation of the
assassination of President John F. Kennedy, it fails miserably. The paper
offers two central conclusions, one which is demonstrably false, and the other
which is specious. The authors opine; ``If the assassination fragments are
derived from three or more separate bullets, then a second assassin is likely,
as the additional bullet would not be attributable to the main suspect, Mr.
Oswald.'' This statement relating to the likelihood of a second assassin based
on the premise of three or more separate bullets is demonstrably false. The
available evidence indicates that Oswald fired three shots, one of which is
believed to have missed. However, on the off chance that all three shots hit
(even though there is absolutely no other supporting forensic evidence for such
a notion) those three shots alone in no way would indicate then that ``a second
assassin is likely.'' The authors' erroneous conclusion was achieved because
they have either been misled (which I personally believe is the case) or they
simply aren't familiar with the evidence.Comment: Published in at http://dx.doi.org/10.1214/07-AOAS153 the Annals of
Applied Statistics (http://www.imstat.org/aoas/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Antimisting kerosene JT3 engine fuel system integration study
An analytical study and laboratory tests were conducted to assist NASA in determining the safety and mission suitability of the modified fuel system and flight tests for the Full-Scale Transport Controlled Impact Demonstration (CID) program. This twelve-month study reviewed and analyzed both the use of antimisting kerosene (AMK) fuel and the incorporation of a fuel degrader on the operational and performance characteristics of the engines tested. Potential deficiencies and/or failures were identified and approaches to accommodate these deficiencies were recommended to NASA Ames -Dryden Flight Research Facility. The result of flow characterization tests on degraded AMK fuel samples indicated levels of degradation satisfactory for the planned missions of the B-720 aircraft. The operability and performance with the AMK in a ground test engine and in the aircraft engines during the test flights were comparable to those with unmodified Jet A. For the final CID test, the JT-3C-7 engines performed satisfactorily while operating on AMK right up to impact
Cepheid theoretical models and observations in HST/WFC3 filters: the effect on the Hubble constant Ho
We present a complete theoretical scenario for classical Cepheids in the most
commonly used HST/WFC3 filters, going from optical (F555W, F606W and F814W) to
near-infrared (F160W) bands. The importance of such a study is related to the
recent release of new classical Cepheids observed with HST/WFC3 in 8 distant
galaxies where SNIa are hosted. These observations have posed sound constraints
to the current distance scale with uncertainties on the Hubble constant Ho
smaller than 3%. Our models explore a large range of metallicity and Helium
content, thus providing a robust and unique theoretical tool for describing
these new and future HST/WFC3 observations. As expected, the Period-Luminosity
(PL) relation in F160W filter is linear and slightly dependent on the
metallicity when compared with optical bands, thus it seems the most accurate
tool to constrain extragalactic distances with Cepheids. We compare the
pulsation properties of Cepheids observed with HST/WFC3-IR with our theoretical
scenario and we discuss the agreement with the predicted Instability Strip for
all the investigated galaxy samples including the case of NGC4258. Finally,
adopting our theoretical F160W PL relation for Z=0.02 and log P>1.0, we derive
new distance moduli. In particular, for NGC 4258, we derive a distance modulus
mu0 = 29.345 +- 0.004 mag with a sigma = 0.34 mag, which is in very good
agreement with the geometrical maser value. Moreover, using the obtained
distance moduli, we estimate the Hubble constant value, Ho=76.0 +- 1.9 km s-1
Mpc-1 in excellent agreement with the most recent literature values.Comment: 13 pages, 9 figures, 4 tables, MNRAS, accepte
Prison? A question instead of a statement
The study concerns the prison space and tries to investigate the main issues related to the detention space and concerning the social, philosophical, territorial, spatial and sensorial aspects of prison
Deterministic Controlled-NOT gate for single-photon two-qubit quantum logic
We demonstrate a robust implementation of a deterministic linear-optical
Controlled-NOT (CNOT) gate for single-photon two-qubit quantum logic. A
polarization Sagnac interferometer with an embedded 45-oriented dove
prism is used to enable the polarization control qubit to act on the momentum
(spatial) target qubit of the same photon. The CNOT gate requires no active
stabilization because the two spatial modes share a common path, and it is used
to entangle the polarization and momentum qubits.Comment: 10 pages, 4 figures. Typos corrected, referee comments and
correction
Statistics of optimal information flow in ensembles of regulatory motifs
Genetic regulatory circuits universally cope with different sources of noise
that limit their ability to coordinate input and output signals. In many cases,
optimal regulatory performance can be thought to correspond to configurations
of variables and parameters that maximize the mutual information between inputs
and outputs. Such optima have been well characterized in several biologically
relevant cases over the past decade. Here we use methods of statistical field
theory to calculate the statistics of the maximal mutual information (the
`capacity') achievable by tuning the input variable only in an ensemble of
regulatory motifs, such that a single controller regulates N targets. Assuming
(i) sufficiently large N, (ii) quenched random kinetic parameters, and (iii)
small noise affecting the input-output channels, we can accurately reproduce
numerical simulations both for the mean capacity and for the whole
distribution. Our results provide insight into the inherent variability in
effectiveness occurring in regulatory systems with heterogeneous kinetic
parameters.Comment: 14 pages, 6 figure
NASA/Pratt and Whitney experimental clean combustor program: Engine test results
A two-stage vorbix (vortex burning and mixing) combustor and associated fuel system components were successfully tested in an experimental JT9D engine at steady-state and transient operating conditions, using ASTM Jet-A fuel. Full-scale JT9D experimental engine tests were conducted in a phase three aircraft experimental clean combustor program. The low-pollution combustor, fuel system, and fuel control concepts were derived from phase one and phase two programs in which several combustor concepts were evaluated, refined, and optimized in a component test rig. Significant pollution reductions were achieved with the combustor which meets the performance, operating, and installation requirements of the engine
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