11,293 research outputs found
Atmospheric turbulence simulation techniques with application to flight analysis
Statistical modeling of atmospheric turbulence is discussed. The statistical properties of atmospheric turbulence, in particular the probability distribution, the spectra, and the coherence are reviewed. Different atmospheric turbulence simulation models are investigated, and appropriate statistical analyses are carried out to verify their validity. The models for simulation are incorporated into a computer model of aircraft flight dynamics. Statistical results of computer simulated landings for an aircraft having characteristics of a DC-8 are reported for the different turbulence simulation techniques. The significance of various degrees of sophistication in the turbulence simulation techniques on the landing performance of the aircraft is discussed
Wind shear modeling for aircraft hazard definition
Mathematical models of wind profiles were developed for use in fast time and manned flight simulation studies aimed at defining and eliminating these wind shear hazards. A set of wind profiles and associated wind shear characteristics for stable and neutral boundary layers, thunderstorms, and frontal winds potentially encounterable by aircraft in the terminal area are given. Engineering models of wind shear for direct hazard analysis are presented in mathematical formulae, graphs, tables, and computer lookup routines. The wind profile data utilized to establish the models are described as to location, how obtained, time of observation and number of data points up to 500 m. Recommendations, engineering interpretations and guidelines for use of the data are given and the range of applicability of the wind shear models is described
Capacity down pipe sustainable drainage system
Abstract: This article describes a water storage and management device. The new technology is centered on a float operated valve. The valve design allows for remote control of a liquid medium with a container. Fluid control device CDP originated to solve the problem of storing water in a space restricted area. The development of the float valve allows the container to self-manage the fluid content
Multispinon continua at zero and finite temperature in a near-ideal Heisenberg chain
The space- and time-dependent response of many-body quantum systems is the
most informative aspect of their emergent behaviour. The dynamical structure
factor, experimentally measurable using neutron scattering, can map this
response in wavevector and energy with great detail, allowing theories to be
quantitatively tested to high accuracy. Here, we present a comparison between
neutron scattering measurements on the one-dimensional spin-1/2 Heisenberg
antiferromagnet KCuF3, and recent state-of-the-art theoretical methods based on
integrability and density matrix renormalization group simulations. The
unprecedented quantitative agreement shows that precise descriptions of
strongly correlated states at all distance, time and temperature scales are now
possible, and highlights the need to apply these novel techniques to other
problems in low-dimensional magnetism
From Instantons to Sphalerons: Time-Dependent Periodic Solutions of SU(2)-Higgs Theory
We solve numerically for periodic, spherically symmetric, classical solutions
of SU(2)-Higgs theory in four-dimensional Euclidean space. In the limit of
short periods the solutions approach tiny instanton-anti-instanton
superpositions while, for longer periods, the solutions merge with the static
sphaleron. A previously predicted bifurcation point, where two branches of
periodic solutions meet, appears for Higgs boson masses larger than .Comment: 14 pages, RevTeX with eps figure
Adjusting bone mass for differences in projected bone area and other confounding variables: an allometric perspective.
The traditional method of assessing bone mineral density (BMD; given by bone mineral content [BMC] divided by projected bone area [Ap], BMD = BMC/Ap) has come under strong criticism by various authors. Their criticism being that the projected bone "area" (Ap) will systematically underestimate the skeletal bone "volume" of taller subjects. To reduce the confounding effects of bone size, an alternative ratio has been proposed called bone mineral apparent density [BMAD = BMC/(Ap)3/2]. However, bone size is not the only confounding variable associated with BMC. Others include age, sex, body size, and maturation. To assess the dimensional relationship between BMC and projected bone area, independent of other confounding variables, we proposed and fitted a proportional allometric model to the BMC data of the L2-L4 vertebrae from a previously published study. The projected bone area exponents were greater than unity for both boys (1.43) and girls (1.02), but only the boy's fitted exponent was not different from that predicted by geometric similarity (1.5). Based on these exponents, it is not clear whether bone mass acquisition increases in proportion to the projected bone area (Ap) or an estimate of projected bone volume (Ap)3/2. However, by adopting the proposed methods, the analysis will automatically adjust BMC for differences in projected bone size and other confounding variables for the particular population being studied. Hence, the necessity to speculate as to the theoretical value of the exponent of Ap, although interesting, becomes redundant
Phenomenology of iron-assisted ion beam pattern formation on Si(001)
Pattern formation on Si(001) through 2 keV Kr+ ion beam erosion of Si(001) at an incident angle of # = 30° and in the presence of sputter codeposition or co-evaporation of Fe is investigated by using in situ scanning tunneling microscopy, ex situ atomic force microscopy and electron microscopy. The phenomenology of pattern formation is presented, and experiments are conducted to rule out or determine the processes of relevance in ion beam pattern formation on Si(001) with impurities. Special attention is given to the determination of morphological phase boundaries and their origin. Height fluctuations, local flux variations, induced chemical inhomogeneities, silicide formation and ensuing composition-dependent sputtering are found to be of relevance for pattern formation
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Phenomenology of iron-assisted ion beam pattern formation on Si(001)
Pattern formation on Si(001) through 2 keV Kr+ ion beam erosion of Si(001) at an incident angle of # = 30° and in the presence of sputter codeposition or co-evaporation of Fe is investigated by using in situ scanning tunneling microscopy, ex situ atomic force microscopy and electron microscopy. The phenomenology of pattern formation is presented, and experiments are conducted to rule out or determine the processes of relevance in ion beam pattern formation on Si(001) with impurities. Special attention is given to the determination of morphological phase boundaries and their origin. Height fluctuations, local flux variations, induced chemical inhomogeneities, silicide formation and ensuing composition-dependent sputtering are found to be of relevance for pattern formation
Copper(I) and Gold(I) Complexes of Aminofunctionalized Phosphinines: Synthesis and Structural Characterization
A series of novel 3-N,N-dimethylaminofunctionalized phosphinines were synthesized and structurally characterized. DFT calculations showed that these aromatic phosphorus heterocycles possess stronger Ï-donor and Ï-donor properties compared to the parent phosphinine C5H5P. With CuBrââ
âSMe2, the corresponding complexes of the type [(phosphinine)2CuBr]2 are formed, which show the classical terminal Ï-coordination mode of the phosphorus donor towards the Cu(I) center. Upon reaction with AuClââ
âSMe2, mononuclear phosphinine-Au(I)Cl complexes could be obtained and crystallographically characterized. Moreover, the presence of a SiMe3-group and a donor-functionality provide the possibility for post-synthetic ligand modifications. With CuClââ
âSMe2 the phosphinine-based hydrochloride salts forms a rare Cu(I) complex with a Cu4Cl4-core, that contains two pairs of differently coordinating phosphinine ligands
Comparative study of selected indoor concentration from selective laser sintering process using virgin and recycled polyamide nylon (pa12)
Additive manufacturing (AM) stands out as one of the promising technologies that
have huge potential towards manufacturing industry. The study on additive manufacturing
impact on the environment and occupational exposure are attracting growing attention recently.
However, most of the researcher focus on desktop and fused deposition modelling type and less
attention given to the industrial type of AM. Usually, during the selective laser sintering process,
recycle powder will be used again to reduce cost and waste. This article compares the PM 2.5,
carbon dioxide (CO2) and total volatile organic compound (TVOC) concentration between virgin
and recycles powder using polyamide-nylon (PA12) towards indoor concentration. Four phases
of sampling involve during air sampling accordingly to the Industry Code of Practice on Indoor
Air Quality 2010 by DOSH Malaysia. It was found that PM 2.5 and CO2
concentration are mainly
generated during the pre-printing process. The recycle powder tended to appear higher compared
to virgin powder in terms of PM 2.5, and CO2. The peak value of PM 2.5 is 1452 ÎŒg/m3 and CO2
is 1218 ppm are obtained during the pre-printing process during 8 hours of sampling. TVOC
concentration from recycling powder is slightly higher during the post- printing phase where
confirm the influence of the powder cake and PA12 temperature from the printing process. In
summary, this work proves that elective laser sintering (SLS) machine operators are exposed to
a significant amount of exposure during the SLS printing process. Mitigation strategies and
personal protective equipment are suggested to reduce occupational exposure
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