bluuebunny/crossref_metadata_2025 huggingface dataset:
Asymptotic behavior of discontinuous solutions in 3-D thermoelasticity with second sound
Authors: Racke Reinhard , Wang Ya-Guang
Published: April 2015

This paper is devoted to the study of the Cauchy problem for linear and semilinear thermoelastic systems with second sound in three space dimensions with discontinuous initial data. Due to Cattaneo’s law, replacing Fourier’s law for heat conduction, the thermoelastic system with second sound is hyperbolic. We investigate the behavior of discontinuous solutions as the relaxation parameter tends to zero, which corresponds to a formal convergence of the system to the hyperbolic-parabolic type of classical thermoelasticity. By studying expansions with respect to the relaxation parameter of the jumps of the potential part of the system on the evolving characteristic surfaces, we obtain that the jump of the temperature goes to zero while the jumps of the heat flux and the gradient of the potential part of the elastic wave are propagated along the characteristic curves of the elastic fields when the relaxation parameter goes to zero. An interesting phenomenon is when time goes to infinity: the behavior will depend on the mean curvature of the initial surface of discontinuity. These jumps decay exponentially when time goes to infinity, more rapidly for a smaller heat conductive coefficient in linear problems and in nonlinear problems when certain growth conditions are imposed on the nonlinear functions.
A derivation of the Aw–Rascle traffic models from Fokker–Planck type kinetic models
Authors: Illner R. , Kirchner C. , Pinnau R.
Published: April 2015

We show how the Aw–Rascle model, a hyperbolic system of PDEs modeling traffic flow, can be derived from a simplified Fokker–Planck type kinetic equation.
Thermo-visco-elasticity at small strains with 𝐿¹-data
Authors: Roubíček Tomáš
Published: April 2015

Existence of a very weak solution to thedd-dimensional thermo-visco-elasticity system for Kelvin-Voigt-type material at small strains involving (possibly nonlinear) monotone viscosity of app-Laplacian type and temperature-dependent heat capacity of an(ω−1)(\omega {-}1)-polynomial growth is proved by a successive passage to a limit in a suitably regularized Galerkin approximation and sophisticated a priori estimates for the temperature gradient performed for the coupled system. A global solution for arbitrarily large data having anL1L^1-structure is obtained under the conditionsp≥2p\ge 2,ω≥1\omega \ge 1, andp>1+d/(2ω)p>1+d/(2\omega ).
Sensitivity equations for a size-structured population model
Authors: Banks H. , Ernstberger Stacey , Hu Shuhua
Published: April 2015

In this paper we consider the classical Sinko-Streifer size-structured population model and derive sensitivity partial differential equations for the sensitivities of solutions with respect to initial conditions, growth rate, mortality rate and fecundity rate. Sample numerical results to illustrate the use of these equations are also presented.
On the stability of Mindlin–Timoshenko plates
Authors: Sare Hugo
Published: April 2015

We consider a Mindlin-Timoshenko model with frictional dissipations acting on the equations for the rotation angles. We prove that this system is not exponentially stable independent of any relations between the constants of the system, which is different from the analogous one-dimensional case. Moreover, we show that the solution decays polynomially to zero, with rates that can be improved depending on the regularity of the initial data.
Kinematics of a shock wave of arbitrary strength in a non-ideal gas
Authors: Pandey Manoj , Sharma V.
Published: April 2015

Singular surface theory is used to study the evolutionary behaviour of an unsteady three-dimensional motion of a shock wave of arbitrary strength propagating through a non-ideal gas. The dynamical coupling between the shock front and the induced discontinuities behind it is investigated by considering an infinite system of transport equations governing the strength of a shock wave and the induced discontinuities behind it. This infinite system, when subjected to a truncation approximation, efficiently describes the shock motion. Disturbances propagating on the shock and the onset of shock-shocks are briefly discussed. For a two-dimensional shock motion, our transport equations bear a structural resemblance to those of geometrical shock dynamics. Attention is drawn to the connection between the transport equation obtained by using the truncation rule and the one obtained by using the characteristic rule. The effects of van der Waals’ excluded volume and wavefront geometry on the evolutionary behaviour of shocks are discussed.
Asymptotics of resonances in a thermoelastic model with light local mass perturbations
Authors: Babych Natalia , Zimmer Johannes
Published: April 2015

The limit behaviour of a linear one-dimensional thermoelastic system with local mass perturbations is studied. The mass density is supposed to be nearly homogeneous everywhere except in an

ε
\varepsilon

-vicinity of a given point, where it is of order

ε

−
m

\varepsilon ^{-m}

, with

m
∈

R

m \in \mathbb {R}

. The resonance vibrations of the string are investigated as

ε
→
0

\varepsilon \to 0

. An important ingredient of the analysis is the construction of an operator in a space of higher regularity such that its spectrum coincides with that of the classical operator in linearised thermoelasticity, with a correspondence of generalised eigenspaces. The convergence of eigenvalues and eigenprojectors is established along with error bounds for two classes of relatively light mass perturbations,

m
>
1

m>1

and

m
=
1

m=1

, which exhibit contrasting limit behaviour.
Asymmetric and moving-frame approaches to Navier-Stokes equations
Authors: Xu Xiaoping
Published: April 2015

In this paper, we introduce a method of imposing asymmetric conditions on the velocity vector with respect to independent variables and a method of moving frame for solving the three-dimensional Navier-Stokes equations. Seven families of non-steady rotating asymmetric solutions with various parameters are obtained. In particular, one family of solutions blows up at any point on a moving plane with a line deleted, which may be used to study turbulence. Using Fourier expansion and two families of our solutions, one can obtain discontinuous solutions that may be useful in the study of shock waves. Another family of solutions are partially cylindrical invariant, contain two parameter functions of

t
t

and structurally depend on two arbitrary polynomials, which may be used to describe incompressible fluid in a nozzle. Most of our solutions are globally analytic with respect to spacial variables.
Asymptotic stability for three-dimensional linear differential systems with time-varying coefficients
Authors: Sugie Jitsuro , Ogami Yuichi
Published: April 2015

This paper is concerned with the asymptotic stability of the zero solution of three-dimensional linear differential systems with variable coefficients. The coefficients are not assumed to be positive. A concept innovated by László Hatvani plays a vital role in our results. Sufficient conditions are also given for the zero solution to be uniformly stable. Some suitable examples are included to illustrate our results. Finally, certain changes of variable are used to broaden the application of our results.
The Euler-Poincaré theory of metamorphosis
Authors: Holm Darryl , Trouvé Alain , Younes Laurent
Published: April 2015

In the pattern matching approach to imaging science, the process of “metamorphosis” is template matching with dynamical templates (Trouvé and Younes, Found. Comp. Math., 2005). Here, we recast the metamorphosis equations of that paper into the Euler-Poincaré variational framework of Holm, Marsden, and Ratiu, Adv. in Math., 1998 and show that the metamorphosis equations contain the equations for a perfect complex fluid (Holm, Springer, 2002). This result connects the ideas underlying the process of metamorphosis in image matching to the physical concept of an order parameter in the theory of complex fluids. After developing the general theory, we reinterpret various examples, including point set, image and density metamorphosis. We finally discuss the issue of matching measures with metamorphosis, for which we provide existence theorems for the initial and boundary value problems.
Kernel sections of multi-valued processes with application to the nonlinear reaction-diffusion equations in unbounded domains
Authors: Wang Yejuan , Zhou Shengfan
Published: April 2015

First, we introduce the concept of pullback

ω
\omega

-limit compactness for multi-valued processes, as an extension of the similar concept in the autonomous and nonautonomous framework. Next, we present the necessary and sufficient conditions (pullback dissipativeness and pullback

ω
\omega

-limit compactness) for the existence of a nonempty local bounded kernel (kernel sections are all compact, invariant and pullback attracting) of an infinite dimensional multi-valued process. In addition, we prove a result ensuring the existence of a uniform attractor and the uniform forward attraction of the inflated kernel sections of a family of multi-valued processes under the general assumptions of point dissipativeness and uniform

ω
\omega

-limit compactness. Finally, we illustrate the abstract theory with a nonlinear reaction-diffusion model in an unbounded domain.
Traveling waves of two-component reaction-diffusion systems arising from higher order autocatalytic models
Authors: Guo Jong-Shenq , Tsai Je-Chiang
Published: April 2015

We study the existence and uniqueness of traveling wave solutions for a class of two-component reaction-diffusion systems with one species being immobile. Such a system has a variety of applications in epidemiology, bio-reactor models, and isothermal autocatalytic chemical reaction systems. Our result not only generalizes earlier results of Ai and Huang (Proceedings of the Royal Society of Edinburgh 2005; 135A:663–675), but also establishes the existence and uniqueness of traveling wave solutions to the reaction-diffusion system for an isothermal autocatalytic chemical reaction of any order in which the autocatalyst is assumed to decay to the inert product at a rate of the same order.
From a multidimensional quantum hydrodynamic model to the classical drift-diffusion equation
Authors: Li Yeping
Published: April 2015

In the paper, we discuss the combined semiclassical and relaxation-time limits of a multidimensional isentropic quantum hydrodynamical model for semiconductors with small momentum relaxation time and Planck constant. The quantum hydrodynamic equations consist of the isentropic Euler equations for the particle density and current density including the quantum Bohn potential and a momentum relaxation term. The momentum equation is highly nonlinear and contains a dispersive term with third-order derivatives. The equations are self-consistently coupled to the Poisson equation for the electrostatic potential. With the help of the Maxwell-type iteration, we prove that, as the Planck constant and the relaxation time tend to zero, periodic initial-value problems of a scaled isentropic quantum hydrodynamic model have unique smooth solutions existing in the time interval where the classical drift-diffusion models have smooth solutions.
Readily computable Green’s and Neumann functions for symmetry-preserving triangles
Authors: Hazlett R. , Babu D.
Published: April 2015

Neumann and Green’s functions of the Laplacian operator on

30
30

-

60
60

-

90

∘

90^{\circ }

and

45
45

-

45
45

-

90

∘

90^{\circ }

triangles can be generated with appropriately placed multiple sources/sinks in a rectangular domain. Highly accurate and easily computable Neumann and Green’s function formulas already exist for rectangles. The extension to equilateral triangles is illustrated. In applications, closed-form expressions can be constructed for the potential, the streamfunction, or the various spatial derivatives of these properties. The derivation of analytic line integrals of these functions allows the proper handling of singularities and facilitates extended applications to problems on domains with open boundaries. Using a boundary integral method, it is demonstrated how one can construct semi-analytical solutions to problems defined on domains that exhibit spatially-dependent properties (heterogeneous media) or possess irregular boundaries.
Energy balance for viscoelastic bodies in frictionless contact
Authors: Stewart David
Published: April 2015

In this paper it is shown that the change in the energy for a linearly viscoelastic body (with Kelvin–Voigt type viscosity) in frictionless contact with a rigid obstacle can be accounted for by viscous losses and the work done by external forces. Thus there is no change in the energy due to impacts, unlike the case of rigid-body dynamics. The result can be extended to a wide class of dynamic viscoelastic boundary thin obstacle problems of similar type.
Versal deformation and static bifurcation diagrams for the cancer cell population model
Authors: Balan Vladimir , Nicola Ileana
Published: April 2015

The paper studies the existence of rest-points and the static bifurcation diagrams of a given nonlinear differential system modeling the cancer cell population evolution from biology. To this aim, the nullclines, the equilibrium points, the transient set, the static bifurcation equation and the associated versal deformation are investigated. The results are further discussed in view of potential applications to cancer therapy.
𝐿^{𝑞}-approach of weak solutions to stationary rotating Oseen equations in exterior domains
Authors: Kračmar S. , Nečasová Š. , Penel P.
Published: April 2015

We establish the existence and uniqueness of a weak solution of the three-dimensional nonhomogeneous stationary Oseen flow around a rotating body in an exterior domain

D
D

. We mainly use the localization procedure (see Kozono and Sohr (1991)) to combine our previous results (see Kračmar, Nečasov á, and Penel (2007, 2008)) with classical results in an appropriate bounded domain. We study the case of a nonintegrable right-hand side, where

f
f

is given in

(

W
^

−
1
,
q

(
D
)

)
3

(\widehat {W}^{-1,q}(D))^3

for certain values of

q
q

.
The Dirichlet problem for Stokes equations outside open arcs in a half-plane and creeping flow over thin profiles
Authors: Krutitskii P.
Published: April 2015

We study the Dirichlet problem for Stokes equations outside curvilinear open arcs in a half-plane. We prove existence and uniqueness of a classical solution to this problem. We obtain integral representation for a solution in the form of potentials, densities in which can be found as a unique solution of the system of the Fredholm integral equations of the second kind and index zero. The creeping flow of viscous fluid over thin profiles is described by the Dirichlet problem studied in this paper.
Energetic properties of the elastic half-space loaded by a periodic distribution of vibrating punches: The study of the phase shift influence
Authors: Scarpetta Edoardo , Sumbatyan Mezhlum
Published: April 2015

We develop an analytical approach to study the wave properties of an elastic half-space subjected to harmonic vibrations applied on its free surface by a periodic array of rigid punches. Contrary to previous investigations, it is assumed that any neighbouring pair of these oscillates with a (common) phase shift, thus implying rather specific behaviours of the structure. Starting from integral equations for the contact stress and representation formulas for the wave field in both theanti-planeandin-planeproblems, suitable mild approximations on the kernels allow analytical solutions of some related (auxiliary) integral equations in a given range of (not too high) frequency.

The explicit formulas thus obtained for the wave field are reflected through some figures and enable us to investigate the energetic properties of the structure with respect to different phase shifts. A direct numerical solution of the original integral equations confirms the precision of the analytical solution.
A local greedy algorithm and higher-order extensions for global numerical continuation of analytically varying subspaces
Authors: Zumbrun Kevin
Published: April 2015

We present a family of numerical implementations of Kato’s ODE propagating global bases of analytically varying invariant subspaces of which the first-order version is a surprisingly simple “greedy algorithm” that is both stable and easy to program and the second-order version a relaxation of a first-order scheme of Brin and Zumbrun. The method has application to numerical Evans function computations used to assess stability of traveling-wave solutions of time-evolutionary PDE.
GRID macroscopic growth law and its application to image inference
Authors: Portman Nataliya , Grenander Ulf , Vrscay Edward
Published: April 2015

In computational anatomy large deformations of anatomical structures observed in images are represented by diffeomorphic flows on the background space of coordinates. They are usually maximum a posteriori (MAP) estimates obtained by minimization of the cost function (posterior energy) consistent with the material properties of an organism. This paper constructs the underlying transformations induced by biological growth according to the Growth as Random Iterated Diffeomorphisms (GRID) model proposed by U. Grenander. They are diffeomorphic flows generated by the GRID macroscopic growth integro-differential equation that emphasizes dependency of the flow on such GRID variables as the Poisson intensity of cell decisions and relative rate of expansion/contraction.

We explore some cost function models that yield biologically meaningful estimates of these growth parameters. Namely, we seek a prior energy that measures cell activities represented by the Poisson intensity function. Using the macroscopic growth law we formulate an optimal control problem where the GRID variables are optimal controls that force an image of the initial organism to be continuously transformed into an image of the grown organism.

We apply the Polak-Ribière conjugate gradient algorithm for direct estimation of the growth parameters from given images. Then the biological mapping is automatically obtained from estimated growth parameters. The accuracy of GRID variable and image estimates obtained by the inference algorithm depends on the value of the weighting coefficient of the prior energy. We propose an experimental evaluation of this coefficient and reveal growth patterns expressed in GRID variables hidden in confocal micrographs of Wingless gene expression patterns in the larval Drosophila wing disc.
Delta shock waves for the chromatography equations as self-similar viscosity limits
Authors: Sun Meina
Published: April 2015

The Riemann problem for the changed form of the chromatography system is considered here. It can be shown that the delta shock wave appears in the Riemann solution for exactly specified initial states. The generalized Rankine-Hugoniot relation of the delta shock wave is derived in detail. The existence and uniqueness of solutions involving the delta shock wave for the Riemann problem is proven by employing the self-similar viscosity vanishing approach.
Asymptotic solution of a nonlinear advection-diffusion equation
Authors: de Loubens R. , Ramakrishnan T.
Published: April 2015

We carry out an asymptotic analysis as

t
→
∞

t\rightarrow \infty

for the nonlinear advection-diffusion equation,

∂
t

u
=
2
α
u

∂
x

u
+

∂
x

(
u

∂
x

u
)

\partial _t u = 2\alpha u \partial _x u + \partial _x(u \partial _x u)

, where

α
\alpha

is a constant. This equation describes the movement of a buoyancy-driven plume in an inclined porous medium, with

α
\alpha

having a specific physical significance related to the bed inclination. For compactly supported initial data, the solution is characterized by two moving boundaries propagating with finite speed and spanning a distance of

O

(

t

)

\mathcal {O}(\sqrt {t})

. We construct an exact outer solution to the PDE that satisfies the right boundary condition. The vanishing condition at the left boundary is enforced by introducing a moving boundary layer, for which we obtain a closed-form expression. The leading-order composite solution is uniformly correct to

O

(
1

/

t

)

\mathcal {O}(1/\sqrt {t})

. A higher-order correction to the inner and the composite solutions is also derived analytically. As a result, we obtain late-time asymptotic expansions for the two moving boundaries, correct to

O

(
1
)

\mathcal {O}(1)

, as well as a composite solution correct to

O

(
1

/

t
)

\mathcal {O}(1/t)

. The findings of this paper are illustrated and verified by numerical computations.
Representation of divergence-free vector fields
Authors: Barbarosie Cristian
Published: April 2015

This paper focuses on a representation result for divergence-free vector fields. Known results are recalled, namely the representation of divergence-free vector fields as curls in two and three dimensions. The representation proposed in the present paper expresses the vector field as an exterior product of gradients and remains valid in arbitrary dimensions. Links to computer graphics and to partial differential equations are discussed.
Global smooth solutions for the compressible viscous and heat-conductive gas
Authors: Qin Yuming , Hu Guili , Wang Taige
Published: April 2015

This paper is concerned with the global existence of smooth solutions to a system of equations describing one-dimensional motion of a self-gravitating, radiative and chemically reactive gas. We have proved that for any arbitrary large smooth initial data, the problem under consideration admits a unique globally smooth (classical) solution. Our results have improved those results by Umehara and Tani ([J. Differential Equations, 234(2007), 439-463; Proc. Japan Acad., 84, Ser. A(2008), 123-128]) and also by Qin, Hu, Huang, and Ma.
Instantaneous shock location and one-dimensional nonlinear stability of viscous shock waves
Authors: Zumbrun Kevin
Published: April 2015

We illustrate in a simple setting the instantaneous shock tracking approach to stability of viscous conservation laws introduced by Howard, Mascia, and Zumbrun. This involves a choice of the definition of instantaneous location of a viscous shock. We show that this choice is time-asymptotically equivalent both to the natural choice of least-squares fit pointed out by Goodman and to a simple phase condition used by Guès, Métivier, Williams, and Zumbrun in other contexts. More generally, we show that it is asymptotically equivalent to any location defined by a localized projection.
“Driving forces” and radiated fields for expanding/shrinking half-space and strip inclusions with general eigenstrain
Authors: Markenscoff Xanthippi , Ni Luqun
Published: April 2015

A half-space constrained Eshelby inclusion (in an infinite elastic matrix) with general uniform eigenstrain (or transformation strain) is analyzed when the plane boundary is moving in general subsonic motion starting from rest. The radiated fields are calculated based on the Willis expression for constrained time-dependent inclusions, which involves the three-dimensional dynamic Green’s function in an infinite traction-free body, and they constitute the unique elastodynamic solution, with initial condition the Eshelby static fields obtained as the unique minimum energy solutions by a limiting process from the spherical inclusion. The mechanical energy-release rate and associated “driving force” to create dynamically an incremental region of eigenstrain (due to any physical process) is calculated for general uniform eigenstrain. For dilatational eigenstrain the solution coincides with the one obtained by a limiting process from a spherically expanding inclusion, while for shear eigenstrain the fields are due to the propagation of the rotation. The “driving force” has the same expression both for expanding and shrinking motions, resulting in expenditure of the energy rate for motion of the boundary in both cases. By superposition from the half-space inclusions, the fields and “driving force” for a strip inclusion with both boundaries moving are obtained. The “driving force” consists also of a contribution from the other boundary when it has time to arrive. The presence of applied loading contributes the counterpart of the Peach-Koehler force of dislocations, in addition to the self-force.
Unilateral dynamic contact of two viscoelastic beams
Authors: Berti Alessia , Naso Maria
Published: April 2015

This work is focused on a dynamic unilateral contact problem between two viscoelastic beams. Global-in-time existence of weak solutions describing the dynamics of the system is established. In addition, asymptotic longtime behavior of weak solutions is discussed: it is shown that the energy solutions decay exponentially to zero under suitable decay properties of the memory kernels.
The one-dimensional flow of a fluid with limited strain-rate
Authors: Farina A. , Fasano A. , Fusi L. , Rajagopal K.
Published: April 2015

We present a model for a continuum in which the strain rate depends linearly on the stress, as long as the latter is below a fixed threshold, but it is frozen to a constant value when the stress exceeds such a threshold. The constitutive equation is given in an implicit form as the stress is a multi-valued function of the strain rate. We derive the model in a general 3D setting and we study the one-dimensional case of a pressure-driven flow between two parallel plates. We prove some analytical results and describe a procedure to determine the main physical parameters (stress threshold and viscosity) by means of a rotational viscometer. Finally we show that the model can be obtained as the limit case of a piecewise linear viscous model.
Centriolar satellite– and hMsd1/SSX2IP-dependent microtubule anchoring is critical for centriole assembly
Authors: Hori Akiko , Peddie Christopher J. , Collinson Lucy M. , Toda Takashi
Published: April 2015

Centriolar satellites are numerous electron-dense granules dispersed around the centrosome. Mutations in their components are linked to various human diseases, but their molecular roles remain elusive. In particular, the significance of spatial communication between centriolar satellites and the centrosome is unknown. hMsd1/SSX2IP localizes to both the centrosome and centriolar satellites and is required for tethering microtubules to the centrosome. Here we show that hMsd1/SSX2IP-mediated microtubule anchoring is essential for proper centriole assembly and duplication. On hMsd1/SSX2IP knockdown, the centriolar satellites become stuck at the microtubule minus end near the centrosome. Intriguingly, these satellites contain many proteins that normally localize to the centrosome. Of importance, microtubule structures, albeit not being anchored properly, are still required for the emergence of abnormal satellites, as complete microtubule depolymerization results in the disappearance of these aggregates from the vicinity of the centrosome. We highlighted, using superresolution and electron microscopy, that under these conditions, centriole structures are faulty. Remarkably, these cells are insensitive to Plk4 overproduction–induced ectopic centriole formation, yet they accelerate centrosome reduplication upon hydroxyurea arrest. Finally, the appearance of satellite aggregates is cancer cell specific. Together our findings provide novel insights into the mechanism of centriole assembly and microtubule anchoring.
Food Security and Teenage Labor Supply
Authors: Hamersma Sarah , Kim Matthew
Published: April 2015

This study assesses whether teenage labor force participation may influence the food security of children in their families. We utilize the Current Population Survey annual Food Security Supplement and linked monthly core data from 2001 through 2012 to assess the year‐to‐year dynamics of food security status in families with teenagers. We estimate the effect of teenage employment on food security while controlling for all time‐invariant individual and household characteristics using a fixed‐effects model. We find that an employed teen reduces the predicted probability of a family's children having very low food security by an economically and statistically significant 50%.
Integrating ontologies of rare diseases and radiological diagnosis
Authors: Kahn Charles E
Published: April 2015

Purpose The author sought to integrate an ontology of rare diseases with a large ontological model of radiological diagnosis.

Materials and Methods The Orphanet Rare Disease Ontology (ORDO) comprised 6794 rare diseases. The Radiology Gamuts Ontology (RGO) incorporated 16 197 terms and 53 425 causal relations linking disorders to imaging manifestations. Semi-automated string-matching was used to match ORDO terms to RGO terms.

Results Of 6794 ORDO terms, 1587 (23.3%) were matched to RGO terms. An additional 700 ORDO terms whose names were hyphenated lists of phenotypic features were added to RGO with causal links from the disease name to the various features. Matched terms were more likely to have higher disease prevalence.

Conclusions Integrating these ontologies expanded the set of terms and scope of knowledge available for radiological differential diagnosis, and can support translational rare-disease research by linking knowledge of genetics and imaging phenotypes.
Managing Complex Contracts: A Theoretical Approach
Authors: Brown Trevor L. , Potoski Matthew , Slyke David Van
Published: April 2015

When a product is difficult to specify in a contract and requires specialized investments for a market exchange, the buyer and seller can find themselves locked into a mutually dependent relationship in which both win-win and lose-lose outcomes are possible. This paper presents a theory of such complex contracting in the public sector and identifies the conditions that increase the likelihood of win-win outcomes for the buyer and the seller. Rules that allow parties to incentivize cooperative behavior increase the chances of a winning outcome. Relationships can promote cooperation if structured to incorporate repeated play and external reputations. Finally, contract success is contingent on mutual understanding between the two parties. Both the buyer and the seller need to understand the rules and the relationship in the same way in order for the exchange to deliver a win-win.
Increased efficiency of
Campylobacter jejuni N
-oligosaccharyltransferase PglB by structure-guided engineering
Authors: Ihssen Julian , Haas Jürgen , Kowarik Michael , Wiesli Luzia , Wacker Michael , Schwede Torsten , Thöny-Meyer Linda
Published: April 2015

Conjugate vaccines belong to the most efficient preventive measures against life-threatening bacterial infections. Functional expression of
N
-oligosaccharyltransferase (
N
-OST) PglB of
Campylobacter jejuni
in
Escherichia coli
enables a simplified production of glycoconjugate vaccines in prokaryotic cells. Polysaccharide antigens of pathogenic bacteria can be covalently coupled to immunogenic acceptor proteins bearing engineered glycosylation sites. Transfer efficiency of PglB

Cj

is low for certain heterologous polysaccharide substrates. In this study, we increased glycosylation rates for
Salmonella enterica
sv. Typhimurium LT2 O antigen (which lacks
N
-acetyl sugars) and
Staphylococcus aureus
CP5 polysaccharides by structure-guided engineering of PglB. A three-dimensional homology model of membrane-associated PglB

Cj

, docked to the natural
C. jejuni N
-glycan attached to the acceptor peptide, was used to identify potential sugar-interacting residues as targets for mutagenesis. Saturation mutagenesis of an active site residue yielded the enhancing mutation N311V, which facilitated fivefold to 11-fold increased
in vivo
glycosylation rates as determined by glycoprotein-specific ELISA. Further rounds of
in vitro
evolution led to a triple mutant S80R-Q287P-N311V enabling a yield improvement of
S. enterica
LT2 glycoconjugates by a factor of 16. Our results demonstrate that bacterial
N
-OST can be tailored to specific polysaccharide substrates by structure-guided protein engineering.
Theoretical constraints on the precision and age range of rehydroxylation dating
Authors: Hare V. J.
Published: April 2015

Accurate and precise dating methods are of central importance to archaeology, palaeontology and earth science. This paper investigates the expected precision and age range of rehydroxylation dating, a recently proposed technique for fired clays. An expression for combined measurement uncertainty is presented, which takes into account all significant sources of experimental uncertainty. Numerical simulations are performed for comparison. Combined measurement uncertainties of approximately 5% with respect to the age of the ceramic should be possible given well-designed experiments. In this case, the most significant contribution to combined measurement uncertainty is from effective lifetime temperature. In addition, it is shown that precision should be acceptable for recently fired material (less than 1 year). Mismatch of balance resolution to sample mass results in large variation in combined relative uncertainties, which vary by four orders of magnitude (approx. 1–1160%) across recent experimental studies, rendering some recently reported dates meaningless. It is recommended that this ratio be less than 10
−6
for a combined relative uncertainty of less than 1%. The age limits of the technique are set by the value of the rate constant and individual sample mineralogy. This theoretical framework should help future interlaboratory comparison as well as optimizing instrument design.
Early-late life trade-offs and the evolution of ageing in the wild
Authors: Lemaître Jean-François , Berger Vérane , Bonenfant Christophe , Douhard Mathieu , Gamelon Marlène , Plard Floriane , Gaillard Jean-Michel
Published: April 2015

Empirical evidence for declines in fitness components (survival and reproductive performance) with age has recently accumulated in wild populations, highlighting that the process of senescence is nearly ubiquitous in the living world. Senescence patterns are highly variable among species and current evolutionary theories of ageing propose that such variation can be accounted for by differences in allocation to growth and reproduction during early life. Here, we compiled 26 studies of free-ranging vertebrate populations that explicitly tested for a trade-off between performance in early and late life. Our review brings overall support for the presence of early-late life trade-offs, suggesting that the limitation of available resources leads individuals to trade somatic maintenance later in life for high allocation to reproduction early in life. We discuss our results in the light of two closely related theories of ageing—the disposable soma and the antagonistic pleiotropy theories—and propose that the principle of energy allocation roots the ageing process in the evolution of life-history strategies. Finally, we outline research topics that should be investigated in future studies, including the importance of natal environmental conditions in the study of trade-offs between early- and late-life performance and the evolution of sex-differences in ageing patterns.
The Evolution of Cooperation by the Hankshaw Effect
Authors: Hammarlund Sarah , Connelly Brian D. , Dickinson Katherine J. , Kerr Benjamin
Published: April 2015

The evolution of cooperation—costly behavior that benefits others—faces one clear obstacle. Namely, cooperators are always at a competitive disadvantage relative to defectors, individuals that reap the same social benefits, but evade the personal cost. One solution to this problem involves genetic hitchhiking, where the allele encoding cooperative behavior becomes linked to a beneficial mutation. While traditionally seen as a passive process driven purely by chance, here we explore a more active form of hitchhiking. Specifically, we model hitchhiking in the context of adaptation to a stressful environment by cooperators and defectors with spatially limited dispersal. Under such conditions, clustered cooperators reach higher local densities, thereby experiencing more opportunities for mutations than defectors. Thus, the allele encoding cooperation has a greater probability of hitchhiking with alleles conferring stress adaptation. We label this probabilistic enhancement the “Hankshaw effect” after the character Sissy Hankshaw, whose anomalously large thumbs made her a singularly effective hitchhiker. Using an agent-based model, we demonstrate that there exists a broad set of conditions allowing the evolution of cooperation through the Hankshaw effect. We discuss the feasibility of our theoretical assumptions for natural systems, not only for the case of cooperation, but also for other costly social behaviors such as spite. The primary elements of our model, including genetic hitchhiking and population structure, have been discussed separately in previous models exploring the evolution of cooperation. However, the combination of these elements has not been appreciated as a solution to the problem of cooperation.
CRISPR with independent transgenes is a safe and robust alternative to autonomous gene drives in basic research
Authors: Port Fillip , Muschalik Nadine , Bullock Simon L
Published: April 2015

CRISPR/Cas technology allows rapid, site-specific genome modification in a wide variety of organisms. CRISPR components produced by integrated transgenes have been shown to mutagenise some genomic target sites inDrosophila melanogasterwith high efficiency, but whether this is a general feature of this system remains unknown. Here, we systematically evaluate available CRISPR/Cas reagents and experimental designs inDrosophila. Our findings allow evidence-based choices of Cas9 sources and strategies for generating knock-in alleles. We perform gene editing at a large number of target sites using a highly active Cas9 line and a collection of transgenic gRNA strains. The vast majority of target sites can be mutated with remarkable efficiency using these tools. We contrast our method to recently developed autonomous gene drive technology for genome engineering (Gantz & Bier, 2015) and conclude that optimised CRISPR with independent transgenes is as efficient, more versatile and does not represent a biosafety risk.
GERV: A Statistical Method for Generative Evaluation of Regulatory Variants for Transcription Factor Binding
Authors: Zeng Haoyang , Hashimoto Tatsunori , Kang Daniel D , Gifford David K
Published: April 2015

The majority of disease-associated variants identified in genome-wide association studies (GWAS) reside in noncoding regions of the genome with regulatory roles. Thus being able to interpret the functional consequence of a variant is essential for identifying causal variants in the analysis of GWAS studies. We present GERV (Generative Evaluation of Regulatory Variants), a novel computational method for predicting regulatory variants that affect transcription factor binding. GERV learns a k-mer based generative model of transcription factor binding from ChIP-seq and DNase-seq data, and scores variants by computing the change of predicted ChIP-seq reads between the reference and alternate allele. The k-mers learned by GERV capture more sequence determinants of transcription factor binding than a motif-based approach alone, including both a transcription factor’s canonical motif as well as associated co-factor motifs. We show that GERV outperforms existing methods in predicting SNPs associated with allele-specific binding. GERV correctly predicts a validated causal variant among linked SNPs, and prioritizes the variants previously reported to modulate the binding of FOXA1 in breast cancer cell lines. Thus, GERV provides a powerful approach for functionally an-notating and prioritizing causal variants for experimental follow-up analysis. The implementation of GERV and related data are available athttp://gerv.csail.mit.edu/
Crossvalidation in Brain Imaging Analysis
Authors: Kriegeskorte Nikolaus
Published: April 2015

Crossvalidation is a method for estimating predictive performance and adjudicating between multiple models. On each of k folds of the process, k-1 of k independent subsets of the data (training set) are used to fit the parameters of each model and the left-out subset (test set) is used to estimate predictive performance. The method is statistically efficient, because training data are reused for testing and performance estimates combined across folds. The method requires no assumptions, provides nearly unbiased (slightly conservative) estimates of predictive performance, and is generally applicable because it amounts to a direct empirical test of each model.
IncreasedRrm2gene dosage reduces fragile site breakage and prolongs survival of ATR mutant mice
Authors: Lopez-Contreras Andres J. , Specks Julia , Barlow Jacqueline H. , Ambrogio Chiara , Desler Claus , Vikingsson Svante , Rodrigo-Perez Sara , Green Henrik , Rasmussen Lene Juel , Murga Matilde , Nussenzweig André , Fernandez-Capetillo Oscar
Published: April 2015

InSaccharomyces cerevisiae, absence of the checkpoint kinase Mec1 (ATR) is viable upon mutations that increase the activity of the ribonucleotide reductase (RNR) complex. Whether this pathway is conserved in mammals remains unknown. Here we show that cells from mice carrying extra alleles of the RNR regulatory subunit RRM2 (Rrm2TG) present supraphysiological RNR activity and reduced chromosomal breakage at fragile sites. Moreover, increasedRrm2gene dosage significantly extends the life span of ATR mutant mice. Our study reveals the first genetic condition in mammals that reduces fragile site expression and alleviates the severity of a progeroid disease by increasing RNR activity.
4,4′-Bipyridine-1,1′-diium acetylenedicarboxylate: a new member of the (H2bipy)[Cu(ox)2] (bipy is 4,4′-bipyridine and ox is oxalate) family
Authors: Chen Xiaocui , Wang Yue , Han Shumin , Wei Yongju , Wang Ruiyao
Published: April 2015

4,4′-Bipyridine-1,1′-diium (H2bipy) acetylenedicarboxylate, C10H12N22+·C4O42−, (1), is a new member of a family of related structures with similar unit-cell parameters. The structures in this family reported previously [Chenet al.(2012).CrystEngComm,14, 6400–6403] are (H2bipy)[Cu(ox)2] (ox is oxalate), (2), (H2bipy)[NaH(ox)2], (3), and (H2bipy)[H2(ox)2], (4). Compound (1) has a one-dimensional structure, in which H2bipy2+cations and acetylenedicarboxylate (ADC2−) anions are linked through a typical supramolecular synthon,i.e.R22(7), and form linear `–cation–anion–' ribbons. Through an array of nonclassical C—H...O hydrogen bonds, adjacent ribbons interact to give two-dimensional sheets. These sheets stack to form a layered structureviaπ–π interactions between the H2bipy2+cations of neighbouring layers. The supramolecular isostructurality of compounds (1)–(4) is ascribed to the synergistic effect of multiple interactions in these structures. The balanced strong and weak intermolecular interactions stabilizing this structure type include strong charge-assisted N—H...O hydrogen bonds, C—H...O contacts and π–π interactions.
What’s the right game? Time-to-market vs “coopetition” in the Myanmar mobile market
Authors: Kumar Ashish , Shankar Ravi , Momaya Kirankumar S.
Published: April 2015

Purpose

– The purpose of this paper is to illustrate, from a Myanmar mobile operator’s point of view, the trade-off between trying to trying to get to untapped towns and villages faster than competition (“time-to-market” strategy) and cooperating with competition through network sharing to reduce costs (“coopetition” strategy).

Design/methodology/approach

– The system dynamics (SD) model shows the business results of a Myanmar mobile operator under two different scenarios, one in which the focus is on time-to-market, and the other in which the focus is on coopetition.

Findings

– An operator motivated by time-to-market advantage expects better margins by capturing market share ahead of competition. However, when every operator follows this individual agenda, its time-to-market benefit depends on whether it is actually faster than competition. In contrast, coopetition eliminates costs by design and provides assured margin improvements.

Practical implications

– The paper establishes that coopetition has a clear economic rationale. Adopting coopetition improves the business case of the mobile operator and helps it to contribute to the socio-economic development of Myanmar.

Originality/value

– The paper applies SD modelling, which is under-represented in marketing, to a study on coopetition in the mobile industry, in the context of Myanmar, a market which is rarely studied in marketing research.
Factors influencing sport tourists’ revisit intentions
Authors: Allameh Sayyed Mohsen , Khazaei Pool Javad , Jaberi Akbar , Salehzadeh Reza , Asadi Hassan
Published: April 2015

Purpose

– The purpose of this paper is to investigate the relationships among destination image, perceived quality, perceived value, satisfaction and revisit intention of sport tourism in Iran.

Design/methodology/approach

– Statistical population of this research consisted of those tourists who traveled to Mazandaran province in Iran as a sport tourism destination in 2012. A random sample of 1,250 tourists was asked to respond to questionnaires from which 886 accurate questionnaires were used for analysing data. Structural equation modeling (SEM) was used to explore the relationships among the research variables.

Findings

– The results showed that sport tourists’ perception of destination image, perceived quality and perceived value influenced their satisfaction and revisit intention positively.

Originality/value

– The results of this research help to better understand the behavioral intentions, which can be an acceptable basis to increase sport tourists’ visit and revisit of a sport destination.
Benchmarking academics through sustainable assessment criteria: an Indian case study
Authors: Singh Bikram Jit , Joshi Rakesh
Published: April 2015

Purpose

– The purpose of this paper is to primarily emphasize on improvement of student’s academic excellence through devising and implementing a competent Internal Assessment Criteria that indirectly improves their results and passing rates in exams.

Design/methodology/approach

– In present system, Internal Assessment Criteria has evolved as critical factor having lot of margin for bringing improvement in student’s academics by redesigning or editing the existing one, appropriately. Assessment criteria are re-optimized by strategic implementation of well proved Six Sigma’s DMAIC approach.

Findings

– It is a one of rarely seen effort to transform Assessment Criteria by identifying the statistical relations between internal marks and external marks secured by students in an end semester university exams. The proposed framework and its validation through an Indian case study, ignites the application of this structured Six Sigma approach in higher education for necessary excellence.

Research limitations/implications

– The whole work revolves around the Indian engineering environments, moreover the case has been restricted and elaborate facts for only unaided (private) engineering universities.

Practical implications

– The paper can be utilized to stimulate thinking about the fine tuning of Assessment Criteria through proven Six Sigma methodology in current Indian academic settings and further safeguarding the interests of managements, students and society, simultaneously.

Originality/value

– The formulation of upcoming challenges before Indian engineering system are outcome of intense literature survey. Focussing on always neglected “Assessment Criteria” and its re-optimization by statistical approach of Six Sigma is hard to found and has immense scope in future for reaching at desired academic hikes.