3,645 research outputs found
Study of experiments on condensation of nitrogen by homogeneous nucleation at states modelling those on the national transonic facility
A cryogenic wind tunnel is based on the twofold idea of lowering drive power and increasing Reynolds number by operating with nitrogen near its boiling point. There are two possible types of condensation problems involved in this mode of wind tunnel operation. They concern the expansion from the nozzle supply to the test section at relatively low cooling rates, and secondly the expansion around models in the test section. This secondary expansion involves higher cooling rates and shorter time scales. In addition to these two condensation problems it is not certain what purity of nitrogen can be achieved in a large facility. Therefore, one cannot rule out condensation processes other than those of homogeneous nucleation
Metamaterial metal-based bolometers
We demonstrate metamaterial metal-based bolometers, which take advantage of
resonant absorption in that a spectral and/or polarization filter can be built
into the bolometer. Our proof-of-principle gold-nanostructure-based devices
operate around 1.5 \mum wavelength and exhibit room-temperature time constants
of about 134 \mus. The ultimate detectivity is limited by Johnson noise,
enabling room-temperature detection of 1 nW light levels within 1 Hz bandwidth.
Graded bolometer arrays might allow for integrated spectrometers with several
octaves bandwidth without the need for gratings or prisms and for integrated
polarization analysis without external polarization optics
Carrier-envelope phase dependence in single-cycle laser pulse propagation with the inclusion of counter-rotating terms
We focus on the propagation properties of a single-cycle laser pulse through
a two-level medium by numerically solving the full-wave Maxwell-Bloch
equations. The counter-rotating terms in the spontaneous emission damping are
included such that the equations of motion are slightly different from the
conventional Bloch equations. The counter-rotating terms can considerably
suppress the broadening of the pulse envelope and the decrease of the group
velocity rooted from dispersion. Furthermore, for incident single-cycle pulses
with envelope area 4, the time-delay of the generated soliton pulse from
the main pulse depends crucially on the carrier-envelope phase of the incident
pulse. This can be utilized to determine the carrier-envelope phase of the
single-cycle laser pulse.Comment: 6 pages, 5 figure
Science requirements and feasibility/design studies of a very-high-altitude aircraft for atmospheric research
The advantages and shortcomings of currently available aircraft for use in very high altitude missions to study such problems as polar ozone or stratosphere-troposphere exchange pose the question of whether to develop advanced aircraft for atmospheric research. To answer this question, NASA conducted a workshop to determine science needs and feasibility/design studies to assess whether and how those needs could be met. It was determined that there was a need for an aircraft that could cruise at an altitude of 30 km with a range of 6,000 miles with vertical profiling down to 10 km and back at remote points and carry a payload of 3,000 lbs
Internationale Förderchancen für Profilbildung und Karriereentwicklung von Nachwuchswissenschaftlern: Vorüberlegungen – Marie- Curie-Förderlinien – ERC Starting Independant Grant – weitere Förderprogramme
Der folgende Beitrag beschreibt die vielfältigen Gestaltungsmöglichkeiten für eine aktive, strukturierte und international ausgerichtete Profil- und Karriereentwicklung von Nachwuchswissenschaftlern. Schwerpunkt ist die ausführliche Vorstellung der Marie-Curie-Individualförderung und der ERC-Nachwuchsgruppen. Darüber hinaus werden sinnvolle Ergänzungs- und Alternativmöglichkeiten im Rahmen weiterer ausgewählter internationaler und nationaler Förderprogramme skizziert
Numerical calculations of effective elastic properties of two cellular structures
Young's moduli of regular two-dimensional truss-like and eye-shape-like
structures are simulated by using the finite element method. The structures are
the idealizations of soft polymeric materials used in the electret
applications. In the simulations size of the representative smallest units are
varied, which changes the dimensions of the cell-walls in the structures. A
power-law expression with a quadratic as the exponential term is proposed for
the effective Young's moduli of the systems as a function of the solid volume
fraction. The data is divided into three regions with respect to the volume
fraction; low, intermediate and high concentrations. The parameters of the
proposed power-law expression in each region are later represented as a
function of the structural parameters, unit-cell dimensions. The presented
expression can be used to predict structure/property relationship in materials
with similar cellular structures. It is observed that the structures with
volume fractions of solid higher than 0.15 exhibit the importance of the
cell-wall thickness contribution in the elastic properties. The cell-wall
thickness is the most significant factor to predict the effective Young's
modulus of regular cellular structures at high volume fractions of solid. At
lower concentrations of solid, eye-like structure yields lower Young's modulus
than the truss-like structure with the similar anisotropy. Comparison of the
numerical results with those of experimental data of poly(propylene) show good
aggreement regarding the influence of cell-wall thickness on elastic properties
of thin cellular films.Comment: 7 figures and 2 table
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