107 research outputs found
An investigation of hydraulic-line resonance and its attenuation
An investigation of fluid resonance in high-pressure hydraulic lines has been made with two types of fluid dampers (or filters) installed in the line. One type involved the use of one or more closed-end tubes branching at right angles from a main line, and the other type was a fluid muffler installed in-line. These devices were evaluated in forced vibration tests with oscillatory disturbances over a 1000-Hz range applied to one end of the line and with oscillatory pressures measured at various stations along the main pipe. Limited applications of acoustic-wave theory to the branched systems are also included. Results show varying attenuations of pressure perturbations, depending on the number and location of branches and the type of muffler. Up to three branches were used in the branch-resonator study, and the largest frequency range with maximum attenuation was obtained for a three-branch configuration. The widest frequency ranges with significant attenuations were obtained with two types of fluid mufflers
Transferable interactions of Li+ and Mg2+ ions in polarizable models
Therapeutic implications of Li(+), in many cases, stem from its ability to inhibit certain Mg(2+)-dependent enzymes, where it interacts with or substitutes for Mg(2+). The underlying details of its action are, however, unknown. Molecular simulations can provide insights, but their reliability depends on how well they describe relative interactions of Li(+) and Mg(2+) with water and other biochemical groups. Here, we explore, benchmark, and recommend improvements to two simulation approaches: the one that employs an all-atom polarizable molecular mechanics (MM) model and the other that uses a hybrid quantum and MM implementation of the quasi-chemical theory (QCT). The strength of the former is that it describes thermal motions explicitly and that of the latter is that it derives local contributions from electron densities. Reference data are taken from the experiment, and also obtained systematically from CCSD(T) theory, followed by a benchmarked vdW-inclusive density functional theory. We find that the QCT model predicts relative hydration energies and structures in agreement with the experiment and without the need for additional parameterization. This implies that accurate descriptions of local interactions are essential. Consistent with this observation, recalibration of local interactions in the MM model, which reduces errors from 10.0 kcal/mol to 1.4 kcal/mol, also fixes aqueous phase properties. Finally, we show that ionâligand transferability errors in the MM model can be reduced significantly from 10.3 kcal/mol to 1.2 kcal/mol by correcting the ligandâs polarization term and by introducing Lennard-Jones cross-terms. In general, this work sets up systematic approaches to evaluate and improve molecular models of ions binding to proteins
The nonlinear time-dependent response of isotactic polypropylene
Tensile creep tests, tensile relaxation tests and a tensile test with a
constant rate of strain are performed on injection-molded isotactic
polypropylene at room temperature in the vicinity of the yield point. A
constitutive model is derived for the time-dependent behavior of
semi-crystalline polymers. A polymer is treated as an equivalent network of
chains bridged by permanent junctions. The network is modelled as an ensemble
of passive meso-regions (with affine nodes) and active meso-domains (where
junctions slip with respect to their positions in the bulk medium with various
rates). The distribution of activation energies for sliding in active
meso-regions is described by a random energy model. Adjustable parameters in
the stress--strain relations are found by fitting experimental data. It is
demonstrated that the concentration of active meso-domains monotonically grows
with strain, whereas the average potential energy for sliding of junctions and
the standard deviation of activation energies suffer substantial drops at the
yield point. With reference to the concept of dual population of crystalline
lamellae, these changes in material parameters are attributed to transition
from breakage of subsidiary (thin) lamellae in the sub-yield region to
fragmentation of primary (thick) lamellae in the post-yield region of
deformation.Comment: 29 pages, 12 figure
Controllable motions of compressible simple materials of various types
It is shown that a motion is possible in every compressible homogeneous isotropic simple solid having a certain range of memory, in the presence of a constant body force field, if and only if it is homogeneous and uniformly accelerated after a certain time. In the class of solids having perfect memory, the only motion of this kind which can be smoothly initiated in a body at rest is a rigid one. For the class of solids having finite memory of duration T and initially at rest, the motions of the type considered need be homogeneous and uniformly accelerated only after time T . For those solids having fading memory, the motion must reduce to a fixed homogeneous deformation. Similar results are developed for simple fluids and anisotropic simple solids. Es wird gezeigt, daĂ in jedem kompressiblen, homogenen und isotropen einfachen Festkörper mit einem gewissen Erinnerungsbereich und in Gegenwart eines konstanten Massenkraftfeldes eine Bewegung dann und nur dann möglich ist, wenn sie homogen und nach einer gewissen Zeit gleichmĂ€Ăig beschleunigt ist. Bei Festkörpern mit vollkommener Erinnerung ist die einzige Bewegung dieser Art, die bei einem ruhenden Körper glatt eingeleitet werden kann, eine starre. Bei Festkörpern mit begrenzter Erinnerungsdauer T , die anfangs in Ruhe waren, mĂŒssen die Bewegungen der betrachteten Art homogen und nur nach der Zeit T gleichmĂ€Ăig beschleunigt sein. FĂŒr Festkörper mit schwindendem GedĂ€chtnis reduziert sich die Bewegung auf eien feste homogene Verformung. Ăhnliche Ergebnisse werden fĂŒr einfache FlĂŒssigkeiten und anisotrope einfache Festkörper entwickelt.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/41721/1/707_2005_Article_BF01204714.pd
Designing spin-spin interactions with one and two dimensional ion crystals in planar micro traps
We discuss the experimental feasibility of quantum simulation with trapped
ion crystals, using magnetic field gradients. We describe a micro structured
planar ion trap, which contains a central wire loop generating a strong
magnetic gradient of about 20 T/m in an ion crystal held about 160 \mu m above
the surface. On the theoretical side, we extend a proposal about spin-spin
interactions via magnetic gradient induced coupling (MAGIC) [Johanning, et al,
J. Phys. B: At. Mol. Opt. Phys. 42 (2009) 154009]. We describe aspects where
planar ion traps promise novel physics: Spin-spin coupling strengths of
transversal eigenmodes exhibit significant advantages over the coupling schemes
in longitudinal direction that have been previously investigated. With a chip
device and a magnetic field coil with small inductance, a resonant enhancement
of magnetic spin forces through the application of alternating magnetic field
gradients is proposed. Such resonantly enhanced spin-spin coupling may be used,
for instance, to create Schr\"odinger cat states. Finally we investigate
magnetic gradient interactions in two-dimensional ion crystals, and discuss
frustration effects in such two-dimensional arrangements.Comment: 20 pages, 13 figure
Active/Passive, âDiminishedâ/âBeautifulâ, âLightâ from Above and Below: Rereading Shekhinahâs Sexual Desire in Zohar al Shir ha-Shirim (Song of Songs)
In Zohar al Shir ha-Shirim, the Zoharâs reading of Song of Songs, Shekhinah, echoing themes associated with the Shulamite of the biblical text, consistently initiates cosmic union. Sexual desire in the zoharic texts is a form of capital necessary to facilitate sefirotic intercourse, although scholarly readings of the zoharic corpus often identify Shekhinah as a passive receptacle. This, however, is only true if the endemic contradictions within the texts are glossed over. In Song of Songs, the Shulamiteâs sexual âinitiativeâ is core. This was not lost on the author(s) of Zohar al Shir ha-Shirim, who, in struggling to explain Shekhinahâs sefirotic role in line with the erotics of Song of Songs, inescapably echoed the âdepatriarchalizingâ themes of the biblical text. As this article demonstrates, in Zohar al Shir ha-Shirim, Shekhinah is active and repeatedly encourages and frustrates cosmic sexual intercourse. Zohar al Shir ha-Shirim shows that it is possible to reread Shekhinahâs role beyond the androcentrism of the authors as well as scholarly assumptions about her passivity
A model for nonlinear viscoelastic torsional response of an elastomeric bushing
An elastomeric bushing is a device used in automotive suspension systems to cushion the loads transmitted from the wheel to the frame of the vehicle. A bushing is essentially an elastomeric hollow cylinder which is bonded to a solid metal shaft at its inner surface and a metal sleeve at its outer surface. The shaft is connected to the suspension and the sleeve is connected to the frame. The elastomeric cylinder provides the cushion when it deforms due to relative motion between the shaft and the sleeve. The relation between the force or moment applied to the shaft or sleeve and the relative displacements or rotations is nonlinear and exhibits features of viscoelasticity.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/41703/1/707_2005_Article_BF01305752.pd
On general measures of deformation
Each particle of a continuum is assigned a second order tensor which is taken as a measure of the deformation of some neighborhood of the particle, and which is determined by a functional depending on the configurations of that neighborhood. Two invariance restrictions are imposed on the functional whose values are spatial strain tensors, that is, associated with the deformed configuration. The first requirement is that a time shift and rigid transformation of the deformed configuration leave the spatial deformation tensor unaltered relative to it. The second requires that if particles of distinct continua undergo the same deformation, the corresponding deformation tensors should be the same. For the special case in which the functional depends on the deformation in the smallest neighborhood of a particle, the restrictions imply that the deformation tensors associated with the deformed and reference configurations are isotropic functions of the left and right Cauchy-Green tensors, respectively. Jedem Teilchen eines Kontinuums wird ein Tensor zweiter Stufe als MaĂ fĂŒr die Deformation einer gewissen Nachbarschaft dieses Teilchen zugeordnet, der durch ein Funktional bestimmt wird, das von der Konfiguration dieser Nachbarschaft abhĂ€ngt. Zwei Invarianzbedingungen werden diesem Funktional, dessen Werte rĂ€umliche Verzerrungstensoren darstellen, auferlegt, und zwar im Hindblick auf die deformierte Konfiguration. Die erste Forderung besagt, daĂ eine Zeitverschiebung und eine starre Transformation der deformierten Konfiguration den rĂ€umlichen Verzerrungstensor im Hinblick auf diese ungeĂ€ndert lassen. Die zweite EinschrĂ€nkung besagt, daĂ entsprechende Deformationstensoren von Partikeln verschiedener Kontinua, die dieselbe Verformung erlitten haben, gleich sein sollen. Im Spezialfall, daĂ die Funktionale nur von der Deformation in der nĂ€chsten Umgebung des Partikels abhĂ€ngen, beinhalten die EinschrĂ€nkungen die Aussage, daĂ die mit dem deformierten und dem undeformierten Zustand verknĂŒpften Deformationstensoren nur isotrope Funktionen des linken und des rechten Cauchy-Green Tensors sein können.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/41717/1/707_2005_Article_BF01172146.pd
The management aspect of psychotherapy with aggressive children
Psychotherapy with an aggressive child may require the imposition of rather firm limitations over aspects of the patient's aggressive behavior. The nature of this management strategy is determined by the individual child's psychopathology. The management aspects of the psychotherapy with two aggressive boys are illustrated in detail. In one case, stringent limitations were imposed when it was discovered that the boy's behavior was regressive and represented an effort to sadistically control people in his environment. In the other case, the behavior was initially left almost unchallenged; this boy's aggressive and delinquent behavior reflected an effort to achieve a sense of order in an inconsistent external and potentially chaotic internal environment.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43969/1/10578_2005_Article_BF01463450.pd
A constitutive representation for linear aging, environmental-dependent viscoelastic materials
This study is concerned with developing a constitutive law for aging and environmental-dependent materials. The development rests on the assumption that the mechanical properties of the aforementioned materials can be mathematically represented by a functional of the strain and environmental histories, and this functional depends on the present time and the time the material is created. This constitutive assumption leads to two equivalent integral forms of the constitutive law after asserting that the functional is linear in the strain history. The first form of the integral law contains a material response functional analogous to the creep and relaxation functions of classical linear viscoelasticity. The second integral law has the same basic mathematical form but the physical interpretation of the mechanical response functional is different. It is demonstrated that both forms of the aging law reduce to the same non-aging law which is the usual starting for an analysis of only environmental-dependent materials. In the Appendix an operator algebra is presented for convenience in manipulating the integral laws for aging materials. Diese Untersuchung beschĂ€ftigt sich mit der Darstellung eines Werkstoffgesetzes fĂŒr Altern und fĂŒr umgebungsabhĂ€ngige Stoffe. Die Entwicklung beruht auf der Annahme, daĂ die mechanischen Eigenschaften der oben erwĂ€hnten Stoffe mathematisch durch ein Funktional der Verzerrungs- und der Umgebungsgeschichten dargestellt werden kann und daĂ dieses Funktional von der augenblicklichen Zeit und der Zeit der Erzeugung des Stoffes abhĂ€ngt. Diese Werkstoffannahme fĂŒhrt, unter der Voraussetzung einer linearen AbhĂ€ngigkeit des Funktionals von der Verzerrungsgeschichte, auf zwei Ă€quivalente Integraldarstellungen des Werkstoffgesetzes. Die erste Darstellung des Integralgesetzes enthĂ€lt ein Materialantwort-Funktional analog der Kriech- und Relaxationsfunktionen der klassischen linearen ViskoelastizitĂ€t. Das zweite Gesetz hat die gleiche mathematische Gestalt, aber verschiedene physikalische Interpretation des mechanischen Antwort-Funktionals. Es wird gezeigt, daĂ fĂŒr nicht-alternde Stoffe beide Darstellungen dasselbe Gesetz, das der ĂŒbliche Ausgangspunkt einer Untersuchung umgebungsbeeinfluĂter Stoffe ist, ergeben. Im Anhang werden einige fĂŒr das Rechnen mit den Integralgesetzen alternder Stoffe handliche SĂ€tze der Operatorenrechnung angegeben.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/41700/1/707_2005_Article_BF01179657.pd
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