Spin polaron in the J1-J2 Heisenberg model

We have studied the validity of the spin polaron picture in the frustrated J1-J2 Heisenberg model. For this purpose, we have computed the hole spectral functions for the Neel, collinear, and disordered phases of this model, by means of the self-consistent Born approximation and Lanczos exact diagonalization on finite-size clusters. We have found that the spin polaron quasiparticle excitation is always well defined for the magnetically ordered Neel and collinear phases, even in the vicinity of the magnetic quantum critical points, where the local magnetization vanishes. As a general feature, the effect of frustration is to increase the amplitude of the multimagnon states that build up the spin polaron wave function, leading to the reduction of the quasiparticle coherence. Based on Lanczos results, we discuss the validity of the spin polaron picture in the disordered phase.Comment: 9 pages, 12 figure

An antibody raised against a pathogenic serpin variant induces mutant-like behaviour in the wild-type protein.

A monoclonal antibody (mAb) that binds to a transient intermediate may act as a catalyst for the corresponding reaction; here we show this principle can extend on a macro-molecular scale to the induction of mutant-like oligomerisation in a wild-type protein. Using the common, pathogenic Glu342Lys (Z) variant of α1-antitrypsin as antigen - whose native state is susceptible to the formation of a proto-oligomeric intermediate - we have produced a mAb (5E3) that increases the rate of oligomerisation of the wild-type (M) variant. Employing ELISA, gel shift, thermal stability and FRET time-course experiments, we show that mAb5E3 does not bind to the native state of α1-antitrypsin, but recognises a cryptic epitope in the vicinity of the post-helix A loop and strand 4C that is revealed upon transition to the polymerisation intermediate, and which persists in the ensuing oligomer. This epitope is not shared by loop-inserted monomeric conformations. We show the increased amenity to polymerisation by either the pathogenic Glu342Lys mutation or the binding of mAb5E3 occurs without affecting energetic barrier to polymerisation. As mAb5E3 also does not alter the relative stability of the monomer to intermediate, it acts in a manner similar to the Glu342Lys mutation, by facilitating the conformational interchange between these two states

Low-energy singlet and triplet excitations in the spin-liquid phase of the two-dimensional J1-J2 model

We analyze the stability of the spontaneously dimerized spin-liquid phase of the frustrated Heisenberg antiferromagnet - the J1-J2 model. The lowest triplet excitation, corresponding to breaking of a singlet bond, is found to be stable in the region 0.38 < J2/J1 < 0.62. In addition we find a stable low-energy collective singlet mode, which is closely related to the spontaneous violation of the discrete symmetry. Both modes are gapped in the quantum disordered phase and become gapless at the transition point to the Neel ordered phase (J2/J1=0.38). The spontaneous dimerization vanishes at the transition and we argue that the disappearance of dimer order is related to the vanishing of the singlet gap. We also present exact diagonalization data on a small (4x4) cluster which indeed show a structure of the spectrum, consistent with that of a system with a four-fold degenerate (spontaneously dimerized) ground state.Comment: 4 pages, 4 figures, small changes, published versio

A study of the temperature dependence of bienzyme systems and enzymatic chains

It is known that most enzyme-facilitated reactions are highly temperature dependent processes. In general, the temperature coefficient, Q10, of a simple reaction reaches 2.0-3.0. Nevertheless, some enzyme-controlled processes have much lower Q10 (about 1.0), which implies that the process is almost temperature independent, even if individual reactions involved in the process are themselves highly temperature dependent. In this work, we investigate a possible mechanism for this apparent temperature compensation: simple mathematical models are used to study how varying types of enzyme reactions are affected by temperature. We show that some bienzyme-controlled processes may be almost temperature independent if the modules involved in the reaction have similar temperature dependencies, even if individually, these modules are strongly temperature dependent. Further, we show that in non-reversible enzyme chains the stationary concentrations of metabolites are dependent only on the relationship between the temperature dependencies of the first and last modules, whilst in reversible reactions, there is a dependence on every module. Our findings suggest a mechanism by which the metabolic processes taking place within living organisms may be regulated, despite strong variation in temperature

Magnetic Impurity in the two-dimensional Heisenberg Antiferromagnet

We analyze the ground state properties of the two-dimensional quantum antiferromagnet with a S=1/2 Kondo impurity. Perturbation theory around the strong Kondo coupling limit is developed and the results compared with studies, based on exact diagonalization of small clusters. We find that at intermediate coupling the impurity is partially screened and the magnetization locally suppressed. A local singlet between the impurity and the host spin is formed asymptotically.Comment: 12 REVTex pages, 4 Postscript figure

At the Origins of the Latvian Orthodox Church: from the “Russian Faith” to Autocephalous Tendencies

The issue of the genesis of the national movement among the Latvian Orthodox population is considered. On the example of the fate of the leaders of the movement for Latvian church independence from Russian Orthodoxy - priest Janis Namnieks and prominent lawyer Janis Davis - the reasons for the appearance of this movement are established, the reasons for the failure of its supporters in 1920 are revealed. It was established that, contrary to popular belief, supporters of an early separation from the Russian Orthodox Church quickly moved from supporting the imperial authorities to the maximum displacement of the “Russian factor” from the life of the Orthodox in the new state - Latvia. It is emphasized that the lack of consolidated support of the secular authorities, the influence of the bishop who came from Russia, the ethnic Latvian John (Pommers), postponed this process for 15 years, and therefore, Latvian Orthodoxy did not go along the beaten path of their Estonian brothers. The attention to the emergence of a historiographic tradition of studying autocephalous tendencies among Latvian Orthodox parishes is paid. A comparison is made of the source base, which was used by researchers to build their own concepts. In addition to research papers and published sources, the article is based on materials from Latvian and Russian archives

Features of Political Transit in the Post-Soviet Space (on the Example of the Pridnestrovian Moldavian Republic and the Donetsk People’s Republic)

The collapse of the USSR led not only to the formation of 15 independent states in the place of the former Soviet republics, but also to the strengthening of secessionism and the emergence of de facto states in the post-Soviet. The emergence, formation and transit of states of this type have many, both common and specific features associated with the peculiarities of their birth.Aim. A comparative analysis of the formation and transit of the Pridnestrovian Moldavian Republic (PMR) and the Donetsk People’s Republic (DPR) as de facto states of the Russian world and a comparative analysis of the formation of industrial models of the economy of the unrecognized states and their management systems.Tasks. Development of models of management systems for the development of the economy of the self-proclaimed republics. Drawing up and substantiation of medium-term forecasts for the development of the PMR and the DPR: 1) integration into a new union state; 2) return to their “mother states” (Moldova and Ukraine); 3) joining Russia, 4) partial international recognition; 5) continuation of existence in the form of a “gray zone” of the economy and politics. Other options are possible, the most tragic of which is the end of support from Russia, which means the end of the existence of these de facto states.Methods. Methods of system analysis, short- and medium-term forecasting, comparative analysis were used.Conclusions. At the heart of any political system is the economy. It is the quality of the constructed economic model that determines the level and duration of the political independence of the state. This connection is especially evident in the construction of the statehood of territorial neoplasms, in which the creation of an economic system is built according to the patterns and principles of the economic system of the patron stateareas”, the shortcomings of the patron state system of the same name, from which the economic model and management mechanisms were “written off”, a comprehensive consideration of the features of secessionism in the specific historical conditions of the emergence of unrecogni zed states is necessary

Excitation spectrum and ground state properties of the S=1/2 Heisenberg ladder with staggered dimerization

We have studied the excitation spectrum of the $S=1/2$ quantum spin ladder with staggered dimerization by dimer series expansions, diagrammatic analysis of an effective interacting Bose gas of local triplets, and exact diagonalization of small clusters. We find that the model has two massive phases, with predominant inter-chain (rung) or intra-chain correlations. The transition from the rung dimer into the intra-chain dimer phase is characterized by softening of the triplet spectrum at $k=\pi$. The excitation spectrum as well as the spin correlations away from and close to the critical line are calculated. The location of the phase boundary is also determined.Comment: 13 pages, 7 figure