Orthopaedic biomaterials play a pivotal role in advancing fracture fixation, joint replacement, and dynamic stabilization within orthopaedic applications. Primarily composed of metals, these biomaterials exhibit outstanding properties including high strength, ductility, fracture toughness, hardness, corrosion resistance, durability, and biocompatibility. Despite their versatility, the landscape of orthopaedic implant materials remains dominated by a limited range of metals, ceramics, composites and polymers. However, the durability of these implants is challenged by biological reactions and material degradation caused by wear and electrochemical corrosion. This article examines the developments that have taken place with respect to the biomaterials and their applications in implants in orthopaedic surgery. This encompasses history, types and properties of metals, polymers, ceramics, composite biomaterials, and processes of fabricating them. The characteristics like biocompatibility, mechanical properties, fluid stability, and the ability to induce osseointegration and the relevance of such materials for implants in orthopaedic surgery is also discussed in this article. Special attention is given to the development of novel bioactive metallic materials and their means of improving wear resistance and biocompatibility by changing the surface and applying coats. The scope of the review further covers advanced technologies including smart bio-materials, 3D/4D printing, use of nanotechnology, and prosthetics. Further, the review article discusses the current status and future trends concerning materials for orthopaedic surgery in greater detail.
We analyse soliton stability in discrete waveguides, revealing the impact of waveguide parameters and nonlinearity. Our analysis reveals the impact of waveguide parameters and nonlinearity on soliton stability, identifying design guidelines for stable propagation.
In this paper, we discuss the morphosyntactic properties and the functional contribution of the discourse-structuring element mat in Lithuanian, which was largely overlooked in previous research. We demonstrate that in each function mat is associated with peculiar morphosyntactic behaviour. We argue that it is the construction in which it occurs as a whole that bears meaning, rather than mat as a lexical unit on its own. In our analysis, we invoke insights and some apparatus of Construction Grammar approaches, which fit well with our observations in their focus on non-compositional aspects of linguistic structure.
We report a quantum phase transition in Pauli limited $d$-wave superconductors and give the mean field estimates of the associated quantum critical point. For a population imbalanced $d$-wave superconductor a stable ground state phase viz. quantum breached pair phase has been identified which comprises of spatial coexistence of gapless superconductivity and nonzero magnetization. Based on the thermodynamic and quasiparticle indicators we for the first time analyze this phase, discuss the thermal behavior of Pauli limited $d$-wave superconductor, give accurate estimates of the thermal scales associated with such systems and map out the pseudogap regime. Our work shows that while the Pauli limited superconductors are known to exhibit exotic modulated superconducting phase at large imbalance of fermion populations; in the regime of weak imbalance an intriguing phase of competing orders is realized. We have established that rather than the superconducting pairing field, it is the average magnetization of the system that quantifies this quantum phase transition. Given that the existing Pauli limited superconductors possess unconventional pairing state symmetry of the superconducting order, our work promises to open up new avenues in the experimental research of these materials. We have also demonstrated an alternate scenario wherein the quantum breached pair phase is a natural outcome for a $d$-wave superconductor with unequal effective masses of the fermion species.
In two recent articles (cond-mat/0606177 and arXiv:0804.1615), we have suggested a unified theory of superconductivity based on the real-space spin-parallel electron pairing and superconducting mechanism and have shown that the stable hexagonal and tetragonal vortex lattices (the optimal doping phases) can be expected in the newly discovered LaO{1-x}F{x}FeAs (x0=1/7=0.1428) and SmO{1-x}F{x}FeAs (x0=1/6=0.1667), respectively. In this paper, we present a theoretical study of the effects of hydrostatic and anisotropic pressure on the superconducting transition temperature Tc of the Fe-based layered superconductors based on the above mentioned theory. Our results indicate a strong doping-dependent pressure effects on the Tc of this compound system. Under high hydrostatic pressure, we find that dTc/dP is negative when x>x0 (the so-called overdoped region) and is positive when x<x0 (the so-called underdoped region). Qualitatively, our finding is in good agreement with the existing experimental data in LaO{1-x}F{x}FeAs (x=0.11<1/7) (arXiv:0803.4266) and SmO{1-x}F{x}FeAs (x=0.13<1/6 and x=0.3>1/6) (arXiv:0804.1582). Furthermore, Tc of both overdoped and underdoped samples shows an increase with uniaxial pressure in the charge stripe direction and a decrease with pressure in the direction perpendicular to the stripes. We suggest that the mechanism responsible for the pressure effect is not specific to the iron-based family and it may also be applicable to other superconducting materials.
Joaquin Garcia, Gloria Subias, Javier Blasco
et al.
In a recent letter, E. Nazarenko et al [Phys. Rev. Lett. 97, 056403 (2006) and cond-mat/0606596] have investigated the low temperature phase of magnetite by means of resonant X-ray scattering. The paper puts forward the quantitative determination of an effective charge ordering (CO) of 0.24 electron among the octahedral iron atoms in the insulating phase. The comment puts in evidence that the analysis performed by Nazarenko et al is wrong and that some of their conclusions are unsupported .
We analyze the phase diagram of superfluidity for two-species fermion mixtures from the Bardeen-Cooper-Schrieffer (BCS) to Bose-Einstein condensation (BEC) limit as a function of scattering parameter, population imbalance and mass anisotropy. We identify regions corresponding to normal, or uniform/non-uniform superfluid phases, and discuss topological quantum phase transitions in the BCS, unitarity and BEC limits. We derive the Ginzburg-Landau equation near the critical temperature, and show that it describes a dilute mixture of paired and unpaired fermions in the BEC limit. We also obtain the zero temperature low frequency and long wavelength collective excitation spectrum, and recover the Bogoliubov relation for weakly interacting dilute bosons in the BEC limit. Lastly, we discuss the effects of harmonic traps and the resulting density profiles in the BEC regime.
K. Alekseev, U. FeodorV.KusmartsevOulu, U. FinlandLoughborough
et al.
We discuss an effect of dc current and dc voltage (stopping bias) generation in a semiconductor superlattice subjected by an ac electric field and its phase-shifted n-th harmonic. In the low field limit, we find a simple dependence of dc voltage on a strength, frequency, and relative phase of mixing harmonics for an arbitrary even value of n. We show that the generated dc voltage has a maximum when a frequency of ac field is of the order of a scattering constant of electrons in a superlattice. This means that for typical semiconductor superlattices at room temperature operating in the THz frequency domain the effect is really observable. We also made a comparison of a recent paper describing an effect of a directed current generation in a semiconductor superlattice subjected by ac field and its second harmonic (n=2) [K.Seeger, Appl.Phys.Lett. 76(2000)82] with our earlier findings describing the same effect [K.Alekseev et al., Europhys. Lett. 47(1999)595; cond-mat/9903092 ]. For the mixing of an ac field and its n-th harmonic with n>=4, we found that additionally to the phase-shift controlling of the dc current, there is a frequency control. This frequency controlling of the dc current direction is absent in the case of n=2. The found effect is that, both the dc current suppression and the dc current reversals exist for some particular values of ac field frequency. For typical semiconductor superlattices such an interesting behavior of the dc current should be observable also in the THz domain. Finally, we briefly review the history of the problem of the dc current generation at mixing of harmonics in semiconductors and semiconductor microstructures.
We reply to a recent comment by H. W. Diehl and M. Shpot (cond-mat/0106502) criticizing our paper J. Phys. A: Math. Gen. 34 (2001) L327-332. We show that the approximation we use for evaluating higher-loop integrals is consistent with homogeneity. A new renormalization group approach is presented in order to compare the two methods with high-precision numerical data concerning the uniaxial case. We stress that the isotropic behaviour cannot be obtained from the anisotropic one.
The symmetry properties of the resistance of mesoscopic samples in the quantum Hall regime are investigated. In addition to the reciprocity relation, our samples obey new symmetries, that relate resistances measured with different contact configurations. Different kinds of symmetries are identified, depending on whether the magnetic field value is such that the system is above, or below, a quantum Hall transition. Related symmetries have recently been reported for macroscopic samples in the quantum Hall regime by Ponomarenko {\it et al.} (Solid State Commun. {\bf 130}, 705 (2004)), and Karmakar {\it et al.} (Preprint cond-mat/0309694).
We show how to simulate numerically both the evolution of 1D quantum systems under dissipation as well as in thermal equilibrium. The method applies to both finite and inhomogeneous systems and it is based on two ideas: (a) a representation for density operators which extends that of matrix product states to mixed states; (b) an algorithm to approximate the evolution (in real or imaginary time) of such states which is variational (and thus optimal) in nature.
A model glass with fast and slow processes is studied. The statics is simple and the facilitated slow dynamics is exactly solvable. The main features of a fragile glass take place: Kauzmann transition, Vogel-Fulcher law, Adam-Gibbs relation and aging. The time evolution can be so slow that a quasi-equilibrium occur at a time dependent effective temperature. The same effective temperature is derived from the Fluctuation-Dissipation ratio, which supports the applicability of out of equilibrium thermodynamics.
Recently Allahverdyan and Nieuwenhuizen (cond-mat/0006404) argued that the second law of thermodynamics may be violated in a quantum system as a "consequence of quantum coherence in the presence of the slightly off-equilibrium nature of the bath." By using a standard result about relative entropy, we prove rigorously that the second law is never violated (and, in particular, a perpetual motion of the second kind can never be realized) in quantum systems no matter how strong ``quantum coherence'' is or no matter how far one goes from equilibrium.
Recently, Schmidt et al. proved that the energy spectrum of a Heisenberg spin system (HSS) is bounded by two parabolas, i.e. lines which depend on the total spin quantum number S as S(S+1). The prove holds for homonuclear HSSs which fulfill a weak homogenity condition. Moreover, the extremal values of the exact spectrum of various HSS which were studied numerically were found to lie on approximate parabolas, named rotational bands, which could be obtained by a shift of the boundary parabolas. In view of this, it has been claimed that the rotational band structure (RBS) of the energy spectrum is a general behavior of HSSs. Furthermore, since the approximate parabolas are very close to the true boundaries of the spectrum for the examples discussed, it has been claimed that the methods allow to predict the detailed shape of the spectrum and related properties for a general HSS. In this comment I will show by means of examples that the RBS hypothesis is not valid for general HSSs. In particular, weak homogenity is neither a necessary nor a sufficient condition for a HSS to exhibit a spectrum with RBS.
We study surface modes of the condensate in the presence of a rotating thermal cloud in an axisymmetric trap. By considering collisions that transfer atoms between the condensate and noncondensate, we find that modes which rotate in the same sense as the thermal cloud damp less strongly than counter-rotating modes. We show that above a critical angular rotation frequency, equivalent to the Landau stability criterion, the co-rotating mode becomes dynamically unstable, leading to the possibility of vortex nucleation. This kind of mechanism is proposed as a natural explanation for the formation of vortices observed recently in the experiment of Haljan \emph{et al} {[}P. C. Haljan \emph{et al.}, cond-mat/0106362{]}. We also generalize our stability analysis to treat the case where the stationary state of the condensate already possesses a single vortex.
This note summarizes some recently published results, that are reported in cond-mat today. Its aim is twofold. First, I believe that it is worthwhile to clarify the theoretical interpretation of a series of x-ray scattering experimental results, whose implications are apparently not well-known in the recent literature. A comment about K edge linear dichroism experiments is also provided. In second place, I would like to add a personal opinion about the role of non-local correlations in the insulating ground-state of V$_2$O$_3$.
There has been a corporative absence of understanding of Hall anomaly data in the mixed state in terms of vortex many-body effect and pinning, because of the dominant theoretical influence. Now D'Anna et al. [ Phys. Rev. Lett. 81, 2530 (1998) (cond-mat/9808164)] are brave enough to announce the prominent role played by vortex many-body effect and pinning in their interpretation of their own data. Here I wish to point out: (1) Indeed the data of D'Anna et al. can be explained within an existing Hall anomaly theory based on vortex many-body considerations; (2) It is not surprising that their data are not consistent with available microscopic Hall anomaly theories, because those theories are mathematically incorrect; and (3) The courage of D'Anna et al. should be appreciated.
The issue of non-analytic corrections to the Fermi-liquid behavior is revisited. Previous studies have indicated that the corrections to the Fermi-liquid forms of the specific heat and the static spin susceptibility scale as $T^{D}$ and $T^{D-1}$, respectively (with extra logarithms for $D=1,3$). In addition, the non-uniform spin susceptibility is expected to depend on the bosonic momentum $Q$ in a non-analytic way, i.e., as $Q^{D-1}$ (again with extra logarithms for $D=1,3$). It is shown that these non-analytic corrections originate from the universal singularities in the dynamical bosonic response functions of a generic Fermi liquid. In contrast to the leading, Fermi-liquid forms which depend on the interaction averaged over the Fermi surface, the non-analytic corrections are parameterized by only two coupling constants, which are the components of the interaction potential at momentum transfers $q=0$ and $q=2k_F$. For 3D systems, a recent result of Belitz, Kirkpatrick and Vojta for the spin susceptibility is reproduced and the issue why a non-analytic momentum dependence of the non-uniform spin susceptibility ($Q^{2}\ln |Q|$) is \emph{not}paralleled by a non-analyticity in the $T-$ dependence ($T^2$) is clarified. For the case of a 2D system with a finite-range interaction, explicit forms of the corrections to the specific heat ($\propto T^2$), uniform ($\propto T$) and non-uniform ($\propto |Q|$) spin susceptibilities are obtained. It is shown that previous calculations of the temperature dependences of these quantities in 2D were incomplete. Some of the results and conclusions of this paper have recently been announced in a short communication [A. V. Chubukov and D. L. Maslov, cond-mat/0304381].
We study the partition functions of quantum impurity problems in the domain of complex applied bias for its relation to the non-equilibrium current suggested by Fendley, Lesage and Saleur (cond-mat/9510055). The problem is reformulated as a certain generalization of the linear response theory that accomodates an additional complex variable. It is shown that the mentioned relation holds in a rather generic case in the linear response limit, or under certain condition out of equilibrium. This condition is trivially satisfied by the quadratic Hamiltonians and is rather restrictive for the interacting models. An example is given when the condition is violated.