bluuebunny/crossref_metadata_2025 huggingface dataset:
Symmetry of tilings of the plane
Authors: Radin Charles
Published: January 2008

We discuss two new results on tilings of the plane. In the first, we give sufficient conditions for the tilings associated with an inflation rule to be uniquely ergodic under translations, the conditions holding for the pinwheel inflation rule. In the second result we prove there are matching rules for the pinwheel inflation rule, making the system the first known to have complete rotational symmetry.
A linear construction for certain Kerdock and Preparata codes
Authors: Calderbank A. R. , Hammons A. R. , Kumar P. Vijay , Sloane N. J. A. , Solé Patrick
Published: January 2008

The Nordstrom-Robinson, Kerdock, and (slightly modified) Preparata codes are shown to be linear over

Z

4

{\mathbb {Z}_4}

, the integers

mod

4

{\bmod \;4}

. The Kerdock and Preparata codes are duals over

Z

4

{\mathbb {Z}_4}

, and the Nordstrom-Robinson code is self-dual. All these codes are just extended cyclic codes over

Z

4

{\mathbb {Z}_4}

. This provides a simple definition for these codes and explains why their Hamming weight distributions are dual to each other. First- and second-order Reed-Muller codes are also linear codes over

Z

4

{\mathbb {Z}_4}

, but Hamming codes in general are not, nor is the Golay code.
A new measure of growth for countable-dimensional algebras
Authors: Hannah John , O’Meara K. C.
Published: January 2008

A new dimension function on countable-dimensional algebras (over a field) is described. Its dimension values for finitely generated algebras exactly fill the unit interval [0, 1]. Since the free algebra on two generators turns out to have dimension 0 (although conceivably some Noetherian algebras might have positive dimension!), this dimension function promises to distinguish among algebras of infinite GK-dimension.
Harmonic analysis of fractal measures induced by representations of a certain 𝐶*-algebra
Authors: Jorgensen Palle E. T. , Pedersen Steen
Published: January 2008

We describe a class of measurable subsets

Ω
\Omega

in

R

d

{\mathbb {R}^d}

such that

L
2

(
Ω
)

{L^2}(\Omega )

has an orthogonal basis of frequencies

e
λ

(
x
)
=

e

i
2
π
∙
x

(
x
∈
Ω
)

{e_\lambda }(x) = {e^{i2\pi \bullet x}}(x \in \Omega )

indexed by

λ
∈
Λ
⊂

R

d

\lambda \in \Lambda \subset {\mathbb {R}^d}

. We show that such spectral pairs

(
Ω
,
Λ
)

(\Omega ,\Lambda )

have a self-similarity which may be used to generate associated fractal measures

μ
\mu

with Cantor set support. The Hilbert space

L
2

(
μ
)

{L^2}(\mu )

does not have a total set of orthogonal frequencies, but a harmonic analysis of

μ
\mu

may be built instead from a natural representation of the Cuntz

C

∗

{{\text {C}}^{\ast }}

-algebra which is constructed from a pair of lattices supporting the given spectral pair

(
Ω
,
Λ
)

(\Omega ,\Lambda )

. We show conversely that such a pair may be reconstructed from a certain Cuntz-representation given to act on

L
2

(
μ
)

{L^2}(\mu )

.
Stokes’ theorem for nonsmooth chains
Authors: Harrison Jenny
Published: January 2008

Much of the vast literature on the integral during the last two centuries concerns extending the class of integrable functions. In contrast, our viewpoint is akin to that taken by Hassler Whitney [Geometric integration theory, Princeton Univ. Press, Princeton, NJ, 1957] and by geometric measure theorists because we extend the class of integrable domains. Let

ω
\omega

be an n-form defined on

R

m

{\mathbb {R}^m}

. We show that if

ω
\omega

is sufficiently smooth, it may be integrated over sufficiently controlled, but nonsmooth, domains

γ
\gamma

. The smoother is

ω
\omega

, the rougher may be

γ
\gamma

. Allowable domains include a large class of nonsmooth chains and topological n-manifolds immersed in

R

m

{\mathbb {R}^m}

. We show that our integral extends the Lebesgue integral and satisfies a generalized Stokes’ theorem.
The Dinitz problem solved for rectangles
Authors: Janssen Jeannette C. M.
Published: January 2008

The Dinitz conjecture states that, for each n and for every collection of n-element sets

S

i
j

{S_{ij}}

, an

n
×
n

n \times n

partial latin square can be found with the

(
i
,
j
)

th

(i,j){\text {th}}

entry taken from

S

i
j

{S_{ij}}

. The analogous statement for

(
n
−
1
)
×
n

(n - 1) \times n

rectangles is proven here. The proof uses a recent result by Alon and Tarsi and is given in terms of even and odd orientations of graphs.
Pseudo-periodic homeomorphisms and degeneration of Riemann surfaces
Authors: Matsumoto Yukio , Montesinos-Amilibia José María
Published: January 2008

We will announce two theorems. The first theorem will classify all topological types of degenerate fibers appearing in one-parameter families of Riemann surfaces, in terms of "pseudoperiodic" surface homeomorphisms. The second theorem will give a complete set of conjugacy invariants for the mapping classes of such homeomorphisms. This latter result implies that Nielsen’s set of invariants [Surface transformation classes of algebraically finite type, Collected Papers 2, Birkhäuser (1986)] is not complete.
Lyapunov theorems for Banach spaces
Authors: Latushkin Yu. , Montgomery-Smith S.
Published: January 2008

We present a spectral mapping theorem for semigroups on any Banach space E. From this, we obtain a characterization of exponential dichotomy for nonautonomous differential equations for E-valued functions. This characterization is given in terms of the spectrum of the generator of the semigroup of evolutionary operators.
Diffeomorphisms of manifolds with finite fundamental group
Authors: Triantafillou Georgia
Published: January 2008

We show that the group

D

(
M
)

\mathcal {D}(M)

of pseudoisotopy classes of diffeomorphisms of a manifold of dimension

≥
5

\geq 5

and of finite fundamental group is commensurable to an arithmetic group. As a result

π
0

(
D
i
f
f

M
)

{\pi _0}(Diff\,M)

is a group of finite type.
The moment map for a multiplicity free action
Authors: Benson Chal , Jenkins Joe , Lipsman Ronald L. , Ratcliff Gail
Published: January 2008

Let K be a compact connected Lie group acting unitarily on a finite-dimensional complex vector space V. One calls this a multiplicity-free action whenever the K-isotypic components of

C

[

V
]

\mathbb {C}{\text {[}}V]

are K-irreducible. We have shown that this is the case if and only if the moment map

τ
:
V
→

k

∗

\tau :V \to {\mathfrak {k}^{\ast } }

for the action is finite-to-one on K-orbits. This is equivalent to a result concerning Gelfand pairs associated with Heisenberg groups that is motivated by the Orbit Method. Further details of this work will be published elsewhere.
Configuration spaces and the space of rational curves on a toric variety
Authors: Guest M. A.
Published: January 2008

The space of holomorphic maps from

S
2

{S^2}

to a complex algebraic variety X, i.e. the space of parametrized rational curves on X, arises in several areas of geometry. It is a well known problem to determine an integer

n
(
D
)

n(D)

such that the inclusion of this space in the corresponding space of continuous maps induces isomorphisms of homotopy groups up to dimension

n
(
D
)

n(D)

, where D denotes the homotopy class of the maps. The solution to this problem is known for an important but special class of varieties, the generalized flag manifolds: such an integer may be computed, and

n
(
D
)
→
∞

n(D) \to \infty

as

D
→
∞

D \to \infty

. We consider the problem for another class of varieties, namely, toric varieties. For smooth toric varieties and certain singular ones,

n
(
D
)

n(D)

may be computed, and

n
(
D
)
→
∞

n(D) \to \infty

as

D
→
∞

D \to \infty

. For other singular toric varieties, however, it turns out that

n
(
D
)

n(D)

cannot always be made arbitrarily large by a suitable choice of D.
An isoperimetric inequality related to Thue’s equation
Authors: Bean Michael A.
Published: January 2008

This paper announces the discovery of an isoperimetric inequality for the area of plane regions defined by binary forms. This result has been applied subsequently in the enumeration of solutions to the Thue inequality and, given its fundamental nature, may find application in other areas as well.
A general decomposition theory for random cascades
Authors: Waymire Edward C. , Williams Stanley C.
Published: January 2008

This announcement describes a probabilistic approach to cascades which, in addition to providing an entirely probabilistic proof of the Kahane-Peyrière theorem for independent cascades, readily applies to general dependent cascades. Moreover, this unifies various seemingly disparate cascade decompositions, including Kahane’s T-martingale decomposition and dimension disintegration.
Chaos in the Lorenz equations: a computer-assisted proof
Authors: Mischaikow Konstantin , Mrozek Marian
Published: January 2008

A new technique for obtaining rigorous results concerning the global dynamics of nonlinear systems is described. The technique combines abstract existence results based on the Conley index theory with computer-assisted computations. As an application of these methods it is proven that for an explicit parameter value the Lorenz equations exhibit chaotic dynamics.
Galois representations and modular forms
Authors: Ribet Kenneth A.
Published: January 2008

In this article, I discuss material which is related to the recent proof of Fermat’s Last Theorem: elliptic curves, modular forms, Galois representations and their deformations, Frey’s construction, and the conjectures of Serre and of Taniyama-Shimura.
Electrostatic effects in unfolded staphylococcal nuclease
Authors: Fitzkee Nicholas C. , García‐Moreno E Bertrand
Published: January 2008

Structure‐based calculations of pK a values and electrostatic free energies of proteins assume that electrostatic effects in the unfolded state are negligible. In light of experimental evidence showing that this assumption is invalid for many proteins, and with increasing awareness that the unfolded state is more structured and compact than previously thought, a detailed examination of electrostatic effects in unfolded proteins is warranted. Here we address this issue with structure‐based calculations of electrostatic interactions in unfolded staphylococcal nuclease. The approach involves the generation of ensembles of structures representing the unfolded state, and calculation of Coulomb energies to Boltzmann weight the unfolded state ensembles. Four different structural models of the unfolded state were tested. Experimental proton binding data measured with a variant of nuclease that is unfolded under native conditions were used to establish the validity of the calculations. These calculations suggest that weak Coulomb interactions are an unavoidable property of unfolded proteins. At neutral pH, the interactions are too weak to organize the unfolded state; however, at extreme pH values, where the protein has a significant net charge, the combined action of a large number of weak repulsive interactions can lead to the expansion of the unfolded state. The calculated pK a values of ionizable groups in the unfolded state are similar but not identical to the values in small peptides in water. These studies suggest that the accuracy of structure‐based calculations of electrostatic contributions to stability cannot be improved unless electrostatic effects in the unfolded state are calculated explicitly.
Critical contribution of VH–VL interaction to reshaping of an antibody: The case of humanization of anti‐lysozyme antibody, HyHEL‐10
Authors: Nakanishi Takeshi , Tsumoto Kouhei , Yokota Akiko , Kondo Hidemasa , Kumagai Izumi
Published: January 2008

To clarify the effects of humanizing a murine antibody on its specificity and affinity for its target, we examined the interaction between hen egg white lysozyme (HEL) and its antibody, HyHEL‐10 variable domain fragment (Fv). We selected a human antibody framework sequence with high homology, grafted sequences of six complementarity‐determining regions of murine HyHEL‐10 onto the framework, and investigated the interactions between the mutant Fvs and HEL. Isothermal titration calorimetry indicated that the humanization led to 10‐fold reduced affinity of the antibody for its target, due to an unfavorable entropy change. Two mutations together into the interface of the variable domains, however, led to complete recovery of antibody affinity and specificity for the target, due to reduction of the unfavorable entropy change. X‐ray crystallography of the complex of humanized antibodies, including two mutants, with HEL demonstrated that the complexes had almost identical structures and also paratope and epitope residues were almost conserved, except for complementary association of variable domains. We conclude that adjustment of the interfacial structures of variable domains can contribute to the reversal of losses of affinity or specificity caused by humanization of murine antibodies, suggesting that appropriate association of variable domains is critical for humanization of murine antibodies without loss of function.
Identification of phosphorylation sites in mammalian mitochondrial ribosomal protein DAP3
Authors: Miller Jennifer L. , Koc Hasan , Koc Emine C.
Published: January 2008

Mammalian mitochondrial ribosomes synthesize 13 proteins that are essential for oxidative phosphorylation. In addition to their role in protein synthesis, some of the mitochondrial ribosomal proteins have acquired functions in other cellular processes such as apoptosis. Death‐associated protein 3 (DAP3), also referred to as mitochondrial ribosomal protein S29 (MRP‐S29), is a GTP‐binding pro‐apoptotic protein located in the small subunit of the ribosome. Previous studies have shown that phosphorylation is one of the most likely regulatory mechanisms for DAP3 function in apoptosis and may be in protein synthesis; however, no phosphorylation sites were identified. In this study, we have investigated the phosphorylation status of ribosomal DAP3 and mapped the phosphorylation sites by tandem mass spectrometry. Mitochondrial ribosomal DAP3 is phosphorylated at Ser215 or Thr216, Ser220, Ser251 or Ser252, and Ser280. In addition, phosphorylation of recombinant DAP3 by Protein kinase A and Protein kinase Cδ at residues that are endogenously phosphorylated in ribosomal DAP3 suggests both of these kinases as potential candidates responsible for the in vivo phosphorylation of DAP3 in mammalian mitochondria. Interestingly, the majority of the phosphorylation sites detected in our study are clustered around the highly conserved GTP‐binding motifs, speculating on the significance of these residues on protein conformation and activity. Site‐directed mutagenesis studies on selected phosphorylation sites were performed to determine the effect of phosphorylation on cell proliferation and PARP cleavage as indication of caspase activation. Overall, our findings suggest DAP3, a mitochondrial ribosomal small subunit protein, is a novel phosphorylated target.
Structural characterization of partially folded intermediates of apomyoglobin H64F
Authors: Schwarzinger Stephan , Mohana‐Borges Ronaldo , Kroon Gerard J.A. , Dyson H. Jane , Wright Peter E.
Published: January 2008

We present a detailed investigation of unfolded and partially folded states of a mutant apomyoglobin (apoMb) where the distal histidine has been replaced by phenylalanine (H64F). Previous studies have shown that substitution of His64, located in the E helix of the native protein, stabilizes the equilibrium molten globule and native states and leads to an increase in folding rate and a change in the folding pathway. Analysis of changes in chemical shift and in backbone flexibility, detected via [1H]‐15N heteronuclear nuclear Overhauser effect measurements, indicates that the phenylalanine substitution has only minor effects on the conformational ensemble in the acid‐ and urea‐unfolded states, but has a substantial effect on the structure, dynamics, and stability of the equilibrium molten globule intermediate formed near pH 4. In H64F apomyoglobin, additional regions of the polypeptide chain are recruited into the compact core of the molten globule. Since the phenylalanine substitution has negligible effect on the unfolded ensemble, its influence on folding rate and stability comes entirely from interactions within the compact folded or partly folded states. Replacement of His64 with Phe leads to favorable hydrophobic packing between the helix E region and the molten globule core and leads to stabilization of helix E secondary structure and overall thermodynamic stabilization of the molten globule. The secondary structure of the equilibrium molten globule parallels that of the burst phase kinetic intermediate; both intermediates contain significant helical structure in regions of the polypeptide that comprise the A, B, E, G, and H helices of the fully folded protein.
Characterization of the post‐translational modification of recombinant human BMP‐15 mature protein
Authors: Saito Seiji , Yano Keiichi , Sharma Shweta , McMahon Heather E. , Shimasaki Shunichi
Published: January 2008

Bone morphogenetic protein‐15 (BMP‐15) is an oocyte‐secreted factor critical for the regulation of ovarian physiology. When recombinant human BMP‐15 (rhBMP‐15) produced in human embryonic kidney 293 cells was subjected to SDS‐PAGE analysis, two mature protein forms corresponding to 16 kDa (P16) and 17 kDa (P17) were observed. Despite the physiological relevance and critical function of BMP‐15 in female reproduction, little is known about the structure of rhBMP‐15. Here, we have analyzed the structure of the rhBMP‐15 mature proteins (P16 and P17) using state‐of‐the‐art proteomics technology. Our findings are as follows: (1) the N‐terminal amino acid of P16 and P17 is pyroglutamic acid; (2) the Ser residue at the sixth position of P16 is phosphorylated; (3) P17 is O‐glycosylated at Thr10; and (4) the C‐terminal amino acid of P16 and P17 is truncated. These findings are the first knowledge of the structure of rhBMP‐15 mature protein toward understanding the molecular basis of BMP‐15 function and could provide an important contribution to the rapidly progressing research area involving oocyte‐specific growth factors in modulation of female fertility.
Solution NMR structure of the N‐terminal domain of the human DEK protein
Authors: Devany Matthew , Kappes Ferdinand , Chen Kuan‐Ming , Markovitz David M. , Matsuo Hiroshi
Published: January 2008

The human DEK protein has a long‐standing association with carcinogenesis since the DEK gene was originally identified in the t(6:9) chromosomal translocation in a subtype of patients with acute myelogenous leukemia (AML). Recent studies have partly unveiled DEK's cellular functions including apoptosis inhibition in primary cells as well as cancer cells, determination of 3′ splice site of transcribed RNA, and suppression of transcription initiation by polymerase II. It has been previously shown that the N‐terminal region of DEK, spanning residues 68–226, confers important in vitro and in vivo functions of DEK, which include double‐stranded DNA (ds‐DNA) binding, introduction of constrained positive supercoils into closed dsDNA, and apoptosis inhibition. In this paper, we describe the three‐dimensional structure of the N‐terminal domain of DEK (DEKntd) as determined using solution NMR. The C‐terminal part of DEKntd, which contains a putative DNA‐binding motif (SAF/SAP motif), folds into a helix‐loop‐helix structure. Interestingly, the N‐terminal part of DEKntd shows a very similar structure to the C‐terminal part, although the N‐terminal and the C‐terminal part differ distinctively in their amino acid sequences. As a consequence, the structure of DEKntd has a pseudo twofold plane symmetry. In addition, we tested dsDNA binding of DEKntd by monitoring changes of NMR chemical shifts upon addition of dsDNAs. We found that not only the C‐terminal part containing the SAF/SAP motif but the N‐terminal part is also involved in DEKntd's dsDNA binding. Our study illustrates a new structural variant and reveals novel dsDNA‐binding properties for proteins containing the SAP/SAF motif.
Unsteady Flow and Dynamic Behavior of Ultrashort Lomakin Gas Bearings
Authors: Teo C. J. , Spakovszky Z. S. , Jacobson S. A.
Published: January 2008

Ultrashort microscale high-speed gas bearings exhibit a whirl instability limit and dynamic behavior much different from conventional hydrostatic gas bearings. In particular, the design space for a stable high-speed operation is confined to a narrow region and involves a singular behavior. The previously developed ultrashort gas bearing theory (Liu et al. (2005, “Hydrostatic Gas Journal Bearings for Micro-Turbomachinery,” ASME J. Vibr. Acoust., 127(2), pp. 157–164)) assumed fully developed flow in the journal bearing gap. There is experimental evidence that this assumption might not be fully applicable for the relatively short flow-through times in such bearings. This has an impact on the estimation of whirl instability onset, bearing operability and power requirements. In this paper, unsteady flow effects in the bearing gap are investigated with the goal to quantify their impact on the bearing dynamic behavior. It is shown that although three-dimensional flow calculations in the ultrashort journal bearing are necessary to quantify the onset of whirl instability, the underlying mechanisms can be qualitatively described by the impulsive starting of a Couette flow. Using this description, two time scales are identified that govern the journal bearing dynamic behavior: the viscous diffusion time and the axial flow-through time. Based on this, a reduced frequency parameter is introduced that determines the development of the flow field in the journal bearing and, together with bearing force models, yields a criterion for whirl instability onset. Detailed three-dimensional computational fluid dynamics calculations of the journal bearing flow have been conducted to assess the criterion. A singular behavior in whirl ratio as a function of the reduced frequency parameter is observed, verifying the refined stability criterion. Using high-fidelity flow calculations, the effects of unsteady journal bearing flow on whirl instability limit and bearing power loss are quantified, and design guidelines and implications on gas bearing modeling are discussed. The stability criterion is experimentally validated demonstrating repeatable, stable high-speed operation of a novel microbearing test device at whirl ratios of 35.
Numerical Analysis on Dynamic Coefficients of Self-Acting Gas-Lubricated Tilting-Pad Journal Bearings
Authors: Lihua Yang , Shemiao Qi , Lie Yu
Published: January 2008

Although gas-lubricated tilting-pad bearings are widely used in high-speed turbomachinery, the theoretical prediction of the dynamic characteristics of tilting-pad gas bearings is also a very difficult problem because of its structural complexity. Several approaches have been proposed to solve this problem such as the pad assembly method and the small perturbation method. A numerical method by combining the partial derivative method with the equivalent coefficient method is presented in this paper to evaluate the dynamic stiffness and damping coefficients of self-acting tilting-pad gas bearing. The dynamic coefficients with the pads fixed and with the pads perturbation are, respectively, obtained for a typical self-acting tilting-pad gas bearing by using the proposed method to mainly explain the dependency of the bearing dynamic coefficients on the perturbation frequency. For bearings with the pads perturbation, the cross-coupling stiffness and damping coefficients are almost negligible compared with the direct ones. At lower perturbation frequency, the stiffness coefficients increase, while the damping coefficients decrease with an increasing frequency. The higher perturbation frequencies have very little effects on the bearing dynamic coefficients. Dynamic stiffness coefficients approach to the constant and damping coefficients to zero. However, with the pads fixed, in a low range of frequency, the absolute values of cross-coupling stiffness coefficients decrease with frequency. Furthermore, the cross-coupling coefficients are not negligible compared with the direct ones. In addition, the effects of pad inertia on dynamic coefficients are studied and compared with the results of pad inertia neglected.
A Simplified One-Dimensional Thermal Model for Journal Bearings
Authors: Liu Daquan , Zhang Wen , Zheng Tiesheng
Published: January 2008

The variational approach, which is used to solve the Reynolds equation based on the assumption of constant temperature, is extended to the generalized Reynolds equation calculation. The direct solution method of the generalized Reynolds equation is presented, where the pressure of the nodal points and the cavitation zone boundary of the film can be determined without iterating. A simplified one-dimensional thermal model is built on the basis of the original two-dimensional thermal model. The model not only concerns the thermal effects of the lubricating film, but also offers a direct and rapid numerical algorithm for solving lubricating film temperature field. The numerical results of the temperature distributions for the one model are in good agreement with experiment, and less computing time is needed.
Effects of Couple Stress on Elastohydrodynamic Lubrication at Impact
Loading
Authors: Chu Hsiao-Ming , Li Wang-Long , Chang Yuh-Ping , Huang Huan-Chang
Published: January 2008

In this paper, pure squeeze elastohydrodynamic lubrication motion of circular contacts with couple stress lubricant is explored at impact loading. On the basis of microcontinuum theory, the transient modified Reynolds equation is derived. Then it is solved simultaneously with the elasticity deformation equation and ball motion equation, thus obtaining the transient pressure profiles, film shapes, normal squeeze velocities, and accelerations. The simulation results reveal that the effect of the couple stress is equivalent to enhancing the lubricant viscosity, which would also enlarge the damper effect. Therefore, as the characteristic length of the couple stress fluid increases, the pressure spike and the dimple form earlier, the maximum pressure and the film thickness increase, and the diameter of the dimple, the rebounding velocity, the maximum value of the relative impact force, and the acceleration decrease. Furthermore, the fact that the contact central pressure for a ball impacting and rebounding from a lubricated surface reached two peaks during the total impact period is proved numerically in this analysis. As the effect of couple stress increases, the first and second peaks form earlier; as the total impact time decreases, the pressure of the first peak increases and that of the second peak decreases. Moreover, the phase shift between the time of the peak value of the squeeze acceleration and the zero value of the squeeze velocity increases with increasing the characteristic length of the couple stress fluid.
Contact Force and Frictional Heating due to “Large” Particles in the Head Disk Interface
Authors: Shen Xinjiang , Bogy David B.
Published: January 2008

Particles in the head disk interface may cause large contact forces acting on the slider as well as thermal asperities in the read/write signal. This is especially true for the close spacing required for 1Tbit∕in.2. In this paper, a three-body contact model is employed to study the effects of a particle entrapped between a slider and a disk. A criterion for determining a particle’s movement pattern is proposed. The study of particles in the head disk interface shows that large particles are likely to slide between the slider and disk interface, and the particles going through the trailing pad of an air bearing slider cause severe contact forces on the slider and generate large heat sources. The frictional heating study shows that the temperature around the magnetoresistive head increases to about 5°C for a single 200nm particle passing through the trailing pad of the slider. The effects of the particle size, disk material, and friction coefficient are also studied. It is found that the disk and slider materials and the frictional coefficient between the materials largely affect the contact force acting on the slider by an entrapped particle as well as the temperature rise at its contact region. It is also found that the friction coefficient largely affects a particle’s movement pattern in the head disk interface.
Thermo-Mechanical Model for Moving Layered Rough Surface Contacts
Authors: Kadiric A. , Sayles R. S. , Ioannides E.
Published: January 2008

A numerical model designed to simulate a moving line contact of two rough layered bodies is presented. Fourier transforms are used to obtain fundamental solutions to relevant differential equations and then these solutions are used as kernel functions in a numerical scheme designed to provide a full thermomechanical solution for real layered contacts. The model assumes steady state heat transfer and predicts contact pressures and deformations, contact temperature rise, and resulting thermal stresses. The heat division between the contacting components is fully accounted for, as are the interactions between the mechanical and thermal displacements. Some results are presented to illustrate the potential importance of a full thermomechanical analysis as compared to a purely mechanical one as well as to demonstrate the influence of coating properties and surface roughness structure on the contact temperatures.
On Elastic Interaction of Nominally Flat Rough Surfaces
Authors: Sepehri A. , Farhang K.
Published: January 2008

A hybrid interactive/optimization technique is used to derive in approximate closed-form equations relating contact load to mean plane separation. Equations governing Hertz contact for the interaction of surface asperities are considered in which asperity shoulder-to-shoulder contact results in normal and tangential components of force. The normal component of asperity force is summed statistically to find total normal force between the two surfaces. The tangential force over a half-plane corresponding to a select direction is found accounting for the directionality of the tangential component of asperity forces. Two sets of approximate equations are found for each of the normal and half-plane tangential force components. The simplest forms of the approximate equations achieve accuracy to within 5% error, while other forms yield approximation error within 0.2%.
Predicting Air Bearing Contamination Using Air Flow Pattern Analysis
Authors: Zhang Shuyu , Strom Brian D.
Published: January 2008

A new method is introduced for predicting particle and liquid droplet contamination on an air bearing surface. The method primarily relies on the analysis of flow patterns nearest the air bearing surface, restricted to two dimensions. In addition, a mathematical model for the vertical flow perpendicular to the disk surface adds clarity to the contamination mechanisms. The predictions compare well with contamination patterns observed in prototype disk drives.
Transient Elastohydrodynamic Lubrication of Hip Joint Implants
Authors: Wang Fengcai , Jin Zhongmin
Published: January 2008

A general transient elastohydrodynamic lubrication model was developed for artificial hip joint implants, particularly in which the three-dimensional time-dependent physiological load and motion components experienced during walking conditions were considered in the theoretical formulation, although only a predominantly vertical load combined with a flexion-extension motion was actually solved. A nominal ball-in-socket configuration was adopted to represent the articulation between the femoral head and the acetabular cup in both simplified and anatomical positions. An appropriate spherical coordinate system and the corresponding mesh grids were used in the general transient lubrication model. Additionally, an equivalent discrete spherical convolution model and the corresponding spherical fast Fourier transform technique were employed to facilitate the evaluation of elastic deformation of spherical bearing surfaces in hip joint implants. The general lubrication model was subsequently applied to investigate the transient lubrication performance of a typical metal-on-metal hip joint implant. The effects of both cup inclination angles in either anatomical or horizontally simplified positions and different lubricant viscosities on the transient elastohydrodynamic lubrication were analyzed under the predominant components of vertically dynamic loading and flexion-extension motion. It was found that the general lubrication model and the numerical methodology were efficient for the transient elastohydrodynamic lubrication analysis during walking condition in hip joint implants. Furthermore, the significant effect of squeeze-film action on maintaining and enhancing the total thin film thickness formation was discussed for the transient lubrication study of the typical hip joint implant.
A Numerical Solution for Quasistatic Viscoelastic Frictional Contact Problems
Authors: Mahmoud Fatin F. , El-Shafei Ahmed G. , Al-Shorbagy Amal E. , Abdel Rahman Alaa A.
Published: January 2008

The tribological aspects of contact are greatly affected by the friction throughout the contact interface. Generally, contact of deformable bodies is a nonlinear problem. Introduction of the friction with its irreversible character makes the contact problem more difficult. Furthermore, when one or more of the contacting bodies is made of a viscoelastic material, the problem becomes more complicated. A nonlinear time-dependent contact problem is addressed. The objective of the present work is to develop a computational procedure capable of handling quasistatic viscoelastic frictional contact problems. The contact problem as a convex programming model is solved by using an adaptive incremental procedure. The contact constraints are incorporated into the model by using the Lagrange multiplier method. In addition, a local-nonlinear nonclassical friction model is adopted to model the friction at the contact interface. This eliminates the difficulties that arise with the application of the classical Coulomb’s law. On the other hand, the Wiechert model, as an effective model capable of describing both creep and relaxation phenomena, is adopted to simulate the linear behavior of viscoelastic materials. The resulting constitutive integral equations are linearized; therefore, complications that arise during the integration of these equations, especially with contact problems, are avoided. Two examples are presented to demonstrate the applicability of the proposed method.
THE SMALL x BEHAVIOR OF THE GLUON STRUCTURE FUNCTION FROM TOTAL CROSS-SECTIONS
Authors: LUNA E. G. S. , NATALE A. A. , ZANETTI C. M.
Published: January 2008

Within a QCD-based eikonal model with a dynamical infrared gluon mass scale we discuss how the small x behavior of the gluon distribution function at moderate Q2 is directly related to the rise of total hadronic cross-sections. In this model the rise of total cross-sections is driven by gluon–gluon semihard scattering processes, where the behavior of the small x gluon distribution function exhibits the power law xg(x, Q2) = h(Q2)x-∊. Assuming that the Q2 scale is proportional to the dynamical gluon mass one, we show that the values of h(Q2) obtained in this model are compatible with an earlier result based on a specific nonperturbative Pomeron model. We discuss the implications of this picture for the behavior of input valence-like gluon distributions at low resolution scales.
ASTROPHYSICAL CONDITION ON THE ATTOLENSING AS A POSSIBLE PROBE FOR A MODIFIED GRAVITY THEORY
Authors: SATO TAKAHIRO , GUNARA BOBBY E. , YAMAMOTO KAZUHIRO , ZEN FREDDY P.
Published: January 2008

We investigate the wave effect in the gravitational lensing by a black hole with very tiny mass less than 10-19 M sun (solar mass), which is called attolensing, motivated by a recent report that the lensing signature might be a possible probe of a modified gravity theory in the braneworld scenario. We focus on the finite source size effect and the effect of the relative motion of the source to the lens, which are influential to the wave effect in the attolensing. Astrophysical condition that the lensed interference signature can be a probe of the modified gravity theory is demonstrated. The interference signature in the microlensing system is also discussed.
New Hypotheses in the Genetics of Psoriasis and Other ‘Complex’ Diseases
Authors: Guilhou Jean-Jacques , Molès Jean-Pierre
Published: January 2008

Psoriasis is a complex genetic disorder in which the disease, according to the current concept, is caused by the interplay of many different genes. However, recent genetic studies indicate that the location of these genes varies considerably among populations and families, raising the question of how the same phenotype can be induced by such variable genetic linkages. To circumvent these discrepancies we propose that psoriasis could be induced by the same repetitive DNA sequence, an endogenous retroviral element present at different locations in the genome. The occurrence of the disease could be linked to an abnormal activation of one or more endogenous retroviral element copies due to their location and/or to modification of their sequence. This unifying concept would simplify our understanding of genetically complex diseases.
The Effect of Imatinib (Glivec®) on Scleroderma and Normal Dermal Fibroblasts: A Preclinical Study
Authors: Soria A. , Cario-André M. , Lepreux S. , Rezvani H.R. , Pasquet J.M. , Pain C. , Schaeverbeke T. , Mahon F.X. , Taïeb A.
Published: January 2008

Background: Scleroderma skin overexpresses the platelet-derived growth factor receptor β-subunit (PDGFR-β) in dermal vessels and PDGFR-β messenger RNA in cultured fibroblasts. Moreover, increased levels of PDGF and stimulatory autoantibodies to PDGFR have been identified in the serum of scleroderma patients. Objective: Imatinib being an inhibitor of tyrosine kinase receptors such as PDGFR, its effect on scleroderma fibroblasts was evaluated in vitro as a preclinical therapeutic step. Methods: The effect of imatinib on fibroblasts grown from normal or involved/uninvolved scleroderma skin was studied by Western blot and the methyltetrazolium test. The pattern of distribution of PDGFR-β in scleroderma versus normal skin was studied by immunohistochemistry. Results: In vitro, imatinib inhibited the proliferation of normal dermal and scleroderma fibroblasts at least partly via the inhibition of the phosphorylation of PDGFR. PDGFR-β was expressed in the epidermis and adnexae in 5 lesional scleroderma biopsies and not in controls. Conclusion: This study suggests that imatinib can serve as therapy to limit dermal fibroblast proliferation in scleroderma.
Medical History, Drug Exposure and the Risk of Psoriasis
Authors: Naldi Luigi , Chatenoud Liliane , Belloni Anna , Peserico Andrea , Balato Nicola , Virgili Anna Rosa , Bruni Pier Luigi , Ingordo Vito , Lo Scocco Giovanni , Solaroli Carmen , Schena Donatella , Di Landro Anna , Pezzarossa Enrico , Arcangeli Fabio , Gianni Claudia , Betti Roberto , Carli Paolo , Farris Alessandro , Barabino Gian Franco , La Vecchia Carlo , Parazzini Fabio
Published: January 2008

Background/Aims: To evaluate the association of psoriasis with selected medical conditions and a number of drugs used before diagnosis. Methods: Multicenter case-control study involving outpatient services of 20 general and teaching hospitals. Entry criteria for cases were a first diagnosis of psoriasis made by a dermatologist and a history of skin manifestations of no more than 2 years after the reported onset of the disease. Controls were the first eligible dermatological patients observed on randomly selected days in the same centers as cases. A total of 560 cases and 690 controls were recruited. Results: The odds ratio (OR) of psoriasis was 0.8 (95% confidence interval, CI, 0.5–1.3) in hypertensive subjects, 1.1 (95% CI 0.6–2.0) in diabetics and 1.1 (95% CI 0.7–1.7) in hyperlipidemic subjects. Histamine 2 receptor antagonist exposure was negatively associated with psoriasis: OR 0.3 (95% CI 0.1–0.8). Conclusion: Our study rules out a strong association of psoriasis at its first ever diagnosis with common chronic conditions. The reported associations of psoriasis with relatively common conditions such as diabetes mellitus, hypertension and hyperlipidemia may represent a late effect of well-known risk factors for psoriasis such as smoking and overweight or reflect factors related to the long course of psoriasis itself.
Pimecrolimus 1% Cream in the Treatment of Facial Psoriasis: A 16-Week Open-Label Study
Authors: Jacobi Arnd , Braeutigam Matthias , Mahler Vera , Schultz Erwin , Hertl Michael
Published: January 2008

Background: Facial psoriasis requires a treatment approach other than topical corticosteroids which bear the risk of skin atrophy. Topical pimecrolimus has been shown to be effective in atopic eczema and recently in psoriasis. Objective: The aim of this open-label single-center investigator-initiated study was to evaluate the efficacy and safety of pimecrolimus 1% cream in patients with facial psoriasis. Methods: 20 adults with facial psoriasis were enrolled. Pimecrolimus 1% cream was applied twice daily to psoriatic lesions of the face over an 8-week period. An 8-week follow-up was added. Results: All clinical parameters showed a significant improvement after 8 and 16 weeks compared to baseline. Pimecrolimus 1% cream was effective and well tolerated. Conclusions: This is the first clinical study with a larger patient cohort reporting a relevant therapeutic effect and favorable safety profile of pimecrolimus 1% cream in facial psoriasis.
Association between Psoriasis and the Metabolic Syndrome
Authors: Cohen A.D. , Sherf M. , Vidavsky L. , Vardy D.A. , Shapiro J. , Meyerovitch J.
Published: January 2008

Background: Previous reports have shown an association between inflammatory diseases such as systemic lupus erythematosus or rheumatoid arthritis and the metabolic syndrome. Recent data demonstrate that psoriasis is an inflammatory disease, suggesting that psoriasis may be one of the components of the metabolic syndrome. Objective: To assess the association between psoriasis and the metabolic syndrome. Methods: A cross-sectional study was performed utilizing the database of the Clalit Health Services. Case patients were defined as patients with a diagnosis of psoriasis vulgaris. Controls were randomly selected from the list of Clalit Health Services enrollees. The proportions of components of the metabolic syndrome (ischemic heart disease, hypertension, diabetes, obesity and dyslipidemia) were compared between case and control patients by univariate analyses. χ2 tests were used to compare categorical parameters between the groups. Logistic and linear regression models served to measure the association between psoriasis and the metabolic syndrome. Results: The study included 16,851 patients with psoriasis and 48,681 controls. In the case group, there were 8,449 men (50.1%) and 8,402 women (49.9%), with a mean age of 42.7 years (SD = 20.3, range = 2–111). Diabetes mellitus was present in 13.8% of the patients with psoriasis as compared to 7.3% of the controls (p < 0.001). Hypertension occurred in 27.5% of the patients with psoriasis and in 14.4% of the controls (p < 0.001). Obesity was present in 8.4% of the patients with psoriasis as opposed to 3.6% of the controls (p < 0.001). Ischemic heart disease was observed in 14.2% of the patients with psoriasis as compared to 7.1% of the controls (p < 0.001). Multivariate models adjusting for age, gender and smoking status of the patients demonstrated that psoriasis was associated with the metabolic syndrome (OR = 1.3, 95% CI = 1.1–1.4), ischemic heart disease (OR = 1.1, 95% CI = 1.0–1.2), diabetes mellitus (OR = 1.2, 95% CI = 1.0–1.3), hypertension (OR = 1.3, 95% CI = 1.2–1.5) and obesity (OR = 1.7, 95% CI = 1.5–1.9). Limitations: The study is designed as a case-control study, thus an association alone was proven and not causality. Conclusion: Our findings demonstrate a possible association between psoriasis and the metabolic syndrome. Appropriate treatment of the metabolic syndrome may be an important part of the management of patients with psoriasis.
Bortezomib-Induced Skin Eruption
Authors: Sanchez-Politta S. , Favet L. , Kerl K. , Dietrich P.-Y. , Piguet V.
Published: January 2008

Bortezomib (Velcade®) is a proteasome inhibitor recently developed and mainly used for the treatment of multiple myeloma. Bortezomib represents a novel class of drugs functioning as proteasome inhibitors. Skin complications of bortezomib treatment are very frequent but poorly characterized. We describe the case of a patient who developed erythematous and edematous plaques after treatment with bortezomib. This case illustrates one of the potential reactions associated with bortezomib administration and underlines the need to recognize and report cutaneous side effects of this new drug.
Increase in Antidepressant Medication in the US Adult Population between 1990 and 2003
Authors: Mojtabai Ramin
Published: January 2008

Background: The rate of antidepressant treatment in the US has significantly increased in the past decade. There are, however, concerns about undertreatment among traditionally underserved groups and overtreatment in less severely ill individuals. This study examines trends in the prevalence of antidepressant drug treatment in two US general population surveys. Methods: The prevalence of antidepressant treatment within a 12-month period was compared in the US National Comorbidity Survey (1990–1992) and the National Comorbidity Survey-Replication (2001–2003). Variations in trends across groups were examined using bivariate and multivariate logistic regression models. Results: The rate of antidepressant drug treatment increased more than four times between early 1990s and early 2000s. The trend was similar across sociodemographic groups. Younger adults, men and racial/ethnic minorities continued to receive antidepressant treatment at a lower rate compared to middle-aged adults, women and non-Hispanic whites, respectively. The rate of antidepressant treatment increased more in the group of less severely ill individuals than in those with more severe psychopathology. Conclusions: Sociodemographic disparities in antidepressant treatment persisted over the last decade in the US, lending support to concerns about undertreatment among traditionally underserved groups, whereas the greater increase in the rate of antidepressant treatment in the less severely ill group lends support to concerns about antidepressant overtreatment in this population.