990 research outputs found
Engine isolation for structural-borne interior noise reduction in a general aviation aircraft
Engine vibration isolation for structural-borne interior noise reduction is investigated. A laboratory based test procedure to simulate engine induced structure-borne noise transmission, the testing of a range of candidate isolators for relative performance data, and the development of an analytical model of the transmission phenomena for isolator design evaluation are addressed. The isolator relative performance test data show that the elastomeric isolators do not appear to operate as single degree of freedom systems with respect to noise isolation. Noise isolation beyond 150 Hz levels off and begins to decrease somewhat above 600 Hz. Coupled analytical and empirical models were used to study the structure-borne noise transmission phenomena. Correlation of predicted results with measured data show that (1) the modeling procedures are reasonably accurate for isolator design evaluation, (2) the frequency dependent properties of the isolators must be included in the model if reasonably accurate noise prediction beyond 150 Hz is desired. The experimental and analytical studies were carried out in the frequency range from 10 Hz to 1000 Hz
Design and test of aircraft engine isolators for reduced interior noise
Improved engine vibration isolation was proposed to be the most weight and cost efficient retrofit structure-borne noise control measure for single engine general aviation aircraft. A study was carried out the objectives: (1) to develop an engine isolator design specification for reduced interior noise transmission, (2) select/design candidate isolators to meet a 15 dB noise reduction design goal, and (3) carry out a proof of concept evaluation test. Analytical model of the engine, vibration isolators and engine mount structure were coupled to an empirical model of the fuselage for noise transmission evaluation. The model was used to develop engine isolator dynamic properties design specification for reduced noise transmission. Candidate isolators ere chosen from available product literature and retrofit to a test aircraft. A laboratory based test procedure was then developed to simulate engine induced noise transmission in the aircraft for a proof of concept evaluation test. Three candidate isolator configurations were evaluated for reduced structure-borne noise transmission relative to the original equipment isolators
Engine-induced structural-borne noise in a general aviation aircraft
Structural borne interior noise in a single engine general aviation aircraft was studied to determine the importance of engine induced structural borne noise and to determine the necessary modeling requirements for the prediction of structural borne interior noise. Engine attached/detached ground test data show that engine induced structural borne noise is a primary interior noise source for the single engine test aircraft, cabin noise is highly influenced by responses at the propeller tone, and cabin acoustic resonances can influence overall noise levels. Results from structural and acoustic finite element coupled models of the test aircraft show that wall flexibility has a strong influence on fundamental cabin acoustic resonances, the lightweight fuselage structure has a high modal density, and finite element analysis procedures are appropriate for the prediction of structural borne noise
Unusual Non-Fermi Liquid Behavior of CeLaNiGe Analyzed in a Single Impurity Anderson Model with Crystal Field Effects
CeNiGe exhibits unusual non-Fermi liquid behavior with the largest
ever recorded value of the electronic specific heat
JKmol without showing any evidence of magnetic order. Specific
heat measurements show that the logarithmic increase of the Sommerfeld
coefficient flattens off below 200 mK. In marked contrast, the local
susceptibility levels off well above 200 mK and already becomes
constant below 1 K. Furthermore, the entropy reaches 2ln2 below 20 K
corresponding to a four level system. An analysis of and was
performed in terms of an single impurity Anderson model with
additional crystal electric field (CEF) splitting. Numerical renormalization
group calculations point to a possible consistent description of the different
low temperature scales in and stemming from the
interplay of Kondo effect and crystal field splitting.Comment: 2 pages, 2 figure
Possible indicators for low dimensional superconductivity in the quasi-1D carbide Sc3CoC4
The transition metal carbide Sc3CoC4 consists of a quasi-one-dimensional (1D)
structure with [CoC4]_{\inft} polyanionic chains embedded in a scandium
matrix. At ambient temperatures Sc3CoC4 displays metallic behavior. At lower
temperatures, however, charge density wave formation has been observed around
143K which is followed by a structural phase transition at 72K. Below T^onset_c
= 4.5K the polycrystalline sample becomes superconductive. From Hc1(0) and
Hc2(0) values we could estimate the London penetration depth ({\lambda}_L ~=
9750 Angstroem) and the Ginsburg-Landau (GL) coherence length ({\xi}_GL ~= 187
Angstroem). The resulting GL-parameter ({\kappa} ~= 52) classifies Sc3CoC4 as a
type II superconductor. Here we compare the puzzling superconducting features
of Sc3CoC4, such as the unusual temperature dependence i) of the specific heat
anomaly and ii) of the upper critical field H_c2(T) at T_c, and iii) the
magnetic hysteresis curve, with various related low dimensional
superconductors: e.g., the quasi-1D superconductor (SN)_x or the 2D
transition-metal dichalcogenides. Our results identify Sc3CoC4 as a new
candidate for a quasi-1D superconductor.Comment: 4 pages, 5 figure
Evolution of Quantum Criticality in CeNi_{9-x}Cu_xGe_4
Crystal structure, specific heat, thermal expansion, magnetic susceptibility
and electrical resistivity studies of the heavy fermion system
CeNi_{9-x}Cu_xGe_4 (0 <= x <= 1) reveal a continuous tuning of the ground state
by Ni/Cu substitution from an effectively fourfold degenerate non-magnetic
Kondo ground state of CeNi_9Ge_4 (with pronounced non-Fermi-liquid features)
towards a magnetically ordered, effectively twofold degenerate ground state in
CeNi_8CuGe_4 with T_N = 175 +- 5 mK. Quantum critical behavior, C/T ~ \chi ~
-ln(T), is observed for x about 0.4. Hitherto, CeNi_{9-x}Cu_xGe_4 represents
the first system where a substitution-driven quantum phase transition is
connected not only with changes of the relative strength of Kondo effect and
RKKY interaction, but also with a reduction of the effective crystal field
ground state degeneracy.Comment: 15 pages, 9 figure
Transport, magnetic, thermodynamic and optical properties in Ti-doped Sr_2RuO_4
We report on electrical resistivity, magnetic susceptibility and
magnetization, on heat capacity and optical experiments in single crystals of
Sr_2Ru_(1-x)Ti_xO_4. Samples with x=0.1 and 0.2 reveal purely semiconducting
resistivity behavior along c and the charge transport is close to localization
within the ab-plane. A strong anisotropy in the magnetic susceptibility appears
at temperatures below 100 K. Moreover magnetic ordering in c-direction with a
moment of order 0.01 mu_B/f.u. occurs at low temperatures. On doping the
low-temperature linear term of the heat capacity becomes reduced significantly
and probably is dominated by spin fluctuations. Finally, the optical
conductivity reveals the anisotropic character of the dc resistance, with the
in-plane conductance roughly following a Drude-type behavior and an insulating
response along c
Poly-MTO, {(CH_3)_{0.92} Re O_3}_\infty, a Conducting Two-Dimensional Organometallic Oxide
Polymeric methyltrioxorhenium, {(CH_{3})_{0.92}ReO_{3}}_{\infty} (poly-MTO),
is the first member of a new class of organometallic hybrids which adopts the
structural pattern and physical properties of classical perovskites in two
dimensions (2D). We demonstrate how the electronic structure of poly-MTO can be
tailored by intercalation of organic donor molecules, such as
tetrathiafulvalene (TTF) or bis-(ethylendithio)-tetrathiafulvalene (BEDT-TTF),
and by the inorganic acceptor SbF. Integration of donor molecules leads to
a more insulating behavior of poly-MTO, whereas SbF insertion does not
cause any significant change in the resistivity. The resistivity data of pure
poly-MTO is remarkably well described by a two-dimensional electron system.
Below 38 K an unusual resistivity behavior, similar to that found in doped
cuprates, is observed: The resistivity initially increases approximately as
ln) before it changes into a dependence below 2 K.
As an explanation we suggest a crossover from purely two-dimensional
charge-carrier diffusion within the \{ReO\} planes at high
temperatures to three-dimensional diffusion at low temperatures in a
disorder-enhanced electron-electron interaction scenario (Altshuler-Aronov
correction). Furthermore, a linear positive magnetoresistance was found in the
insulating regime, which is caused by spatial localization of itinerant
electrons at some of the Re atoms, which formally adopt a electronic
configuration. X-ray diffraction, IR- and ESR-studies, temperature dependent
magnetization and specific heat measurements in various magnetic fields suggest
that the electronic structure of poly-MTO can safely be approximated by a
purely 2D conductor.Comment: 15 pages, 16 figures, 2 table
Water-content related alterations in macro and micro scale tendon biomechanics
Though it is known that the water content of biological soft tissues alters mechanical properties, little attempt has been made to adjust the tissue water content prior to biomechanical testing as part of standardization procedures. The objective of this study was to examine the effects of altered water content on the macro and micro scale mechanical tissues properties. Human iliotibial band samples were obtained during autopsies to osmotically adapt their water content. Macro mechanical tensile testing of the samples was conducted with digital image correlation, and micro mechanical tests using atomic force microscopy. Analyses were conducted for elastic moduli, tensile strength, and strain at maximum force, and correlations for water content, anthropometric data, and post-mortem interval. Different mechanical properties exist at different water concentrations. Correlations to anthropometric data are more likely to be found at water concentrations close to the native state. These data underline the need for adapting the water content of soft tissues for macro and micro biomechanical experiments to optimize their validity. The osmotic stress protocol provides a feasible and reliable standardization approach to adjust for water content-related differences induced by age at death, post-mortem interval and tissue processing time with known impact on the stress-strain properties
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