Presence Of Transition Research Articles

Resilience of the superradiant phase against A2 effects in the quantum Rabi dimer

We explore the quantum criticality of a two-site model combining quantum Rabi models with hopping interaction. Through a combination of analytical and numerical approaches, we find that the model allows the appearance of a superradiant quantum phase transition (QPT) even in the presence of strong $\mathbf{A}^2$ terms, preventing single-site superradiance. In the two-site model the effect of $\mathbf{A}^2$ terms can be surmounted by the photon delocalization from hopping, and a reversed superradiant QPT occurs as a consequence of the competition between $\mathbf{A}^2$ terms and the hopping interaction. We characterize the phase diagram and scaling functions, and extract the critical exponents in the vicinity of the critical point, thus establishing the universal behavior of the second-order phase transition. Remarkably the effective hopping strength will be enhanced if more cavities are cascaded. We also prove that the multi-qubit counterpart of the quantum Rabi dimer, i.e., the Dicke dimer, has the same properties in beating the $\mathbf{A}^2$ effect. Our work provides a way to the study of phase transitions in presence of the $\mathbf{A}^2$ terms and offers the prospect of investigating quantum-criticality physics and quantum devices in many-body systems.

Conformational dynamics of p53 N-terminal TAD2 region under different solvent conditions

Although the mystery molecule p53 has been studied extensively, still several unknown mechanisms need to be elucidated. Being a central hub of cellular signaling pathways, the function of p53 is precisely executed synergistically by its intrinsically disordered and structural domains. The disordered N-terminal region further modulates p53 function by undergoing promiscuous binding and folding with several partners with the help of TAD1 and TAD2 motifs. Among these regions, a significant contribution is made by TAD2 in terms of binding affinities. This heterogeneity in p53 TAD region motivates to employ a reductionist approach to understand the folding behavior of TAD2 region independently under a broad range of different pH, temperature and solvent conditions. Since the intracellular environment is complex and crowded with a variety of molecules providing different type of surfaces from polar to hydrophobic, it is mandatory to characterize the conformational heterogeneity of disordered proteins to completely understand their function. Different types of alcohols were used to estimate the structure forming capabilities of the TAD2 peptides using circular dichroism, fluorescence and lifetime spectroscopy. The alcohols ethanol, TFE and HFIP were previously known to induce increasing levels of hydrophobic environments in water-alcohol mixtures respectively. Our results have shown that TAD2 peptide undergoes a dehydration dependent induction of hydrophobic interactions leading towards structural transitions in presence of organic solvents. This study is highlighting the importance of hydrophobic surfaces playing a crucial role in TAD2 interaction and conformational transitions.

The critical behaviors and the scaling functions of a coalescence equation* * Partially supported by NSFC grant Nos. 11771286 and 11531001.

We show that a coalescence equation exhibits a variety of critical behaviors, depending on the initial condition. This equation was introduced a few years ago to understand a toy model studied by Derrida and Retaux to mimic the depinning transition in presence of disorder. It was shown recently that this toy model exhibits the same critical behaviors as the equation studied in the present work. Here we find several families of exact solutions of this coalescence equation, in particular a family of scaling functions which are closely related to the different possible critical behaviors. These scaling functions lead to new conjectures, in particular on the shapes of the critical trees, that we have checked numerically.

Numerical Methods for Antiferromagnets

Compared with ferromagnetic counterparts, antiferromagnetic materials are considered as the future of spintronic applications since these materials are robust against the magnetic perturbation, produce no stray field, and display ultrafast dynamics. There are (at least) two sets of magnetic moments in antiferromagnets (with magnetization of the same magnitude but antiparallel directions) and ferrimagnets (with magnetization of the different magnitude). The coupled dynamics for the bipartite collinear antiferromagnets is modeled by a coupled system of Landau-Lifshitz-Gilbert equations with an additional term originated from the antiferromagnetic exchange, which leads to femtosecond magnetization dynamics. In this paper, we develop three Gauss-Seidel projection methods for micromagnetics simulation in antiferromagnets and ferrimagnets. They are first-order accurate in time and second-order in space, and only solve linear systems of equations with constant coefficients at each step. Femtosecond dynamics, N\'{e}el wall structure, and phase transition in presence of an external magnetic field for antiferromagnets are provided with the femtosecond stepsize.

4f–4f Spectral Analysis and Solvent Effect for the Interaction of Pr(III) with l-Tryptophan Using Different Aquated Solvents in the Presence and Absence of Zn(II)

In this study, the absorption spectra due to the interaction between Pr(III) and l-tryptophan system exhibiting 4f–4f transitions in presence and absence of Zn(II) using different aquated organic solvents such as methanol, dioxane, acetonitrile and N,N-dimethylformamide (DMF) were investigated and the same were also analyzed for the equimolar mixtures (1:1) of two different solvents. The energy parameters such as Slater–Condon (FK) factor, Lande spin–orbit coupling constant ($$\xi_{4f}$$), Nephelauxetic ratio ($$\beta )$$, bonding parameter (b1/2) and percent covalency ($$\delta )$$, are also calculated and the observed variation in these parameters with the change of solvents indicates the nature of bond formed between Pr(III) and l-tryptophan. The oscillator strength (P) and Judd–Ofelt parameters Tλ (λ = 2, 4, 6) have also been determined for the four transitions namely 3H4 to 3P2, 3P1, 3P0 and 1D2.The solvent DMF has the most effective for the promotion of 4f–4f electric dipole intensity. Comparative absorption spectra of Pr(III):l-Tryptophan in different solvents.

The role of isoaspartate in fibrillation and its prevention by Protein-L-isoaspartyl methyltransferase

BackgroundIsomerization of aspartate to isoaspartate (isoAsp) on aging causes protein damage and malfunction. Protein-L-isoaspartyl methyltransferase (PIMT) performs a neuroprotective role by repairing such residues. A hexapeptide, Val-Tyr-Pro-(isoAsp)-His-Ala (VA6), a substrate of PIMT, is shown to form fibrils, while the normal Asp-containing peptide does not. Considering the role of PIMT against epileptic seizure, the combined effect of PIMT and two antiepileptic drugs (AEDs) (valproic acid and stiripentol) was investigated for anti-fibrillation activity. MethodsStructural/functional modulations due to the binding of AEDs to PIMT were investigated using biophysical techniques. Thioflavin T (ThT) fluorescence assay and microscopic methods were employed to study fibril formation by VA6. In vitro experiments with PC12 cells were carried out with PIMT/AEDs. ResultsThT assay indicated reduction of fibrillation of VA6 by PIMT. AEDs stabilize PIMT, bind close to the cofactor binding site, possibly exerting allosteric effect, increase the enzymatic activity, and anti-fibrillation efficacy. Furthermore, Aβ42, implicated in Alzheimer's disease, undergoes β-sheet to α-helix transition in presence of PIMT. Studies with PC12 derived neurons showed that PIMT and PIMT/AEDs exerted neuroprotective effect against anti-NGF induced neurotoxicity. This was further validated against neurotoxicity induced by Aβ42 in primary rat cortical neurons. ConclusionsThe study provides a new perspective to the role isoAsp in protein fibrillation, PIMT in its prevention and AEDs in enhancing the activity of the enzyme. General significanceIsoAsp, with an additional C atom in the main-chain of polypeptide chain, may make it more susceptible to fibrillation. PIMT alone, or in association with AEDs prevents this.

Sequence-specific B-to-Z transition in self-assembled DNA: A biophysical and thermodynamic study

The most remarkable conformational transition in nature is the B-to-Z transition of DNA which not only contributes for epigenetic regulation but also is exploited to create several advanced nanomaterials for sensing and nanomechanics. The present communication focuses on the intrinsic factors that control the La3+/Ce3+-induced B-to-Z transition in self-assembled branched DNA (bDNA) nanostructures. The transition is sensitive even to two nucleotide change in the loop length and overhang sequences. Predominantly, bDNA structures having 3 T loop length are more sensitive towards helical switching than the 5 T bearing structures. Particularly, bDNA US-17, US-19 and US-23 having 3 T in the loop are showing B-Z transition in presence of LaCl3. Interestingly, with ‘GATC’ overhangs both La3+/Ce3+-induced B-to-Z transition was noticed in bDNA structures US-21 and US-22 (having 3 T and 5 T in the loop, respectively). The lanthanide-induced B-Z transition in bDNA is reversed with treatment of EDTA. Isothermal titration calorimetry (ITC) experiments show that the binding mode of lanthanide salts to bDNA followed an entropically and enthalpically favorable process. Further, for the first time ITC data suggests the B-to-Z transition in bDNA is a cooperative shift from exothermic to endothermic.

A priori estimates in Sobolev spaces for a class of hyperbolic operators in presence of transition

We establish several a priori estimates of local or global nature in Sobolev spaces with general exponent [Formula: see text] for a class of second-order hyperbolic operators with double characteristics in presence of a transition in a domain of the Euclidian space [Formula: see text].

Criterion for the occurrence of many-body localization in the presence of a single-particle mobility edge

Non-interacting fermions in one dimension can undergo a localization-delocalization transition in the presence of a quasi-periodic potential as a function of that potential. In the presence of interactions, this transition transforms into a Many-Body Localization (MBL) transition. Recent studies have suggested that this type of transition can also occur in models with quasi-periodic potentials that possess single particle mobility edges. Two such models were studied in PRL 115,230401(2015) but only one was found to exhibit an MBL transition in the presence of interactions while the other one did not. In this work we investigate the occurrence of MBL in the presence of weak interactions in five different models with single particle mobility edges in one dimension with a view to obtaining a criterion for the same. We find that not all such models undergo a thermal-MBL phase transition in presence of weak interactions. We propose a criterion to determine whether MBL is likely to occur in presence of interaction based only on the properties of the non-interacting models. The relevant quantity $\epsilon$ is a measure of how localized the localized states are relative to how delocalized the delocalized states are in the non-interacting model. We also study various other features of the non-interacting models such as the divergence of the localization length at the mobility edge and the presence or absence of `ergodicity' and localization in their many-body eigenstates. However, we find that these features cannot be used to predict the occurrence of MBL upon the introduction of weak interactions.

Comparison of Gabay–Toulouse and de Almeida–Thouless instabilities for the spin-glass XY model in a field on sparse random graphs

Vector spin glasses are known to show two different kinds of phase transitions in presence of an external field: the so-called de Almeida-Thouless and Gabay-Toulouse lines. While the former has been studied to some extent on several topologies (fully connected, random graphs, finite-dimensional lattices, chains with long-range interactions), the latter has been studied only in fully connected models, which however are known to show some unphysical behaviors (e.g. the divergence of these critical lines in the zero-temperature limit). Here we compute analytically both these critical lines for XY spin glasses on random regular graphs. We discuss the different nature of these phase transitions and the dependence of the critical behavior on the field distribution. We also study the crossover between the two different critical behaviors, by suitably tuning the field distribution.

Utilizing a non-equilibrium phase transition for one-step synthesis of metal nano-crystals

One-step synthesis of nanocrystals with tunable morphology is an area of both basic and technological interest, the former due to the lack of our understanding regarding the pre-conditions and the mechanism through which entropy is reduced spontaneously and the free energy becomes enthalpy-driven, while the latter stems from the need to grow nanocrystals reproducibly and without external adducts for seeding. Here we will present and discuss results of using the liquid crystalline material MBBA (N-(4-methoxybenzylidene)-4-butylaniline) as a matrix for the synthesis of Au and Ag nanocrystals of tunable morphology. MBBA lacks the smectic phase in its phase diagram and has only the nematic and isotropic phases as equilibrium phases while the other phases are non-equilibrium or glassy phases. We have proved that even the nematic-isotropic phase transition is a non-equilibrium transition that can, however, be turned into an equilibrium transition in presence of enthalpic forces. Using this self-organizing property and the fact that the imine group in MBBA is a reducing agent, we have grown Au and Ag nanocrystals, as also Au-Ag core-shell nanocrystals, of a number of shapes that can be tuned by the temperature and the time of growth. The principle behind the method can be utilized for one-step nanocrystal synthesis in general. In particular, the simultaneous growth of the core and the shell in the highly miscible metals shows that the non-equilibrium conditions set a differential in the growth rates of Au and Ag, causing phase segregation.

Conformational transition of κ-casein in micellar environment: Insight from the tryptophan fluorescence

Intrinsically disordered proteins (IDPs) are under intense analysis due to their structural flexibility and importance in biological functions. Minuscule modulation in the microenvironment induces significant conformational changes in IDPs, and these non-native conformations of the IDPs often induce aggregation and cause cell death. Changes in the membrane composition often change the microenvironment, which promote conformational change and aggregation of IDPs. κ-Casein, an important milk protein, belongs to the class of IDPs containing net negative charges. In this present work, we have studied the interaction of κ-casein with cetyltrimethyl ammonium bromide (CTAB), a positively charged surfactant, utilizing various steady state fluorescence, time-resolved fluorescence and circular dichroism spectroscopy. Our results clearly indicate that κ-casein undergoes at least two conformational transitions in presence of various concentrations of CTAB. The intrinsically disordered κ-casein assumes a partially folded conformation at lower concentration of CTAB, which adopts an unstructured conformation at higher concentration of CTAB. The partially folded conformation of κ-casein at a lower CTAB concentration might be induced by the favorable electrostatic interaction between the positively charged surfactant headgroup and net negative charges of the protein, whereas surfactant nature of CTAB is being pronounced at higher concentration of CTAB.

Influence of graphene growth temperature by chemical vapour deposition on the hydrogen response of palladium–graphene junction

The hydrogen sensing by palladium-graphene junction was dependent on the atmospheric pressure chemical vapour deposition growth temperature of the graphene films. The growth temperature window adopted in this study was 900–1000 °C, and the hydrogen sensor performance of the palladium–graphene junction (0.5–2.0% H2 in air) was studied in the temperature range 30–150 °C. Raman spectroscopy study with the as grown graphene films revealed the multilayer nature and the Pd–graphene planar structure showed a temperature dependent n- to p-type conductivity change in presence of hydrogen. Such a conductivity transition in presence of a reducing gas like hydrogen was experimentally studied in detail, and the hydrogen sensor results were correlated with the multilayer character of the graphene thin film, which induces hydrogen intercalation between the graphene layers.

Anatase-to-rutile transition in co-doped TiO2 pigments

In this paper, cobalt-doped titanium dioxide green ceramic pigments were synthesized by the polymeric precursor method. In order to investigate the obtainment of a crystalline rutile phase and particles in nanoscale, a chromophore doping was made with fixed concentrations of 1, 2, and 4 mol%, utilizing a calcination temperature of 600oC. The products were investigated by thermal analysis, X-ray diffraction, diffuse reflectance, scanning and transmission electron microscopies. The titanium dioxide:cobalt crystallite size was about 65–100 nm. A broad reflectance band around 540 nm (green region) was observed for all doped samples, indicating the appearance of a deep green pigment. Furthermore, the results have shown that cobalt-doped titanium dioxide promotes greater phase conversion of anatase to rutile. Samples submitted at a temperature of 600 °C, pure titanium dioxide contains 22% rutile, whereas titanium dioxide: 4% of cobalt contains 78% rutile. The mechanism of phase transition in presence of cobalt is attributed to the lower valences of the dopant (II or III) when compared to the titanium valence (IV). Ionic substitution leads to the generation of oxygen vacancies that promote phase transitions at lower temperatures than expected in pure titanium dioxide.

Displacement crackles within the temporomandibular joint and the quality of abduction and adduction mandible track in functional tests, using Zebris JMA device. Part II

Aim of the study. The aim of the first part of the study was to evaluate the impact of displacement crackles, located within the temporomandibular joint, on the quality of graphic records, free mandible movements, recorded with a Zebris JMA device and to determine the usefulness of instrumental techniques in the analysis of functional diagnosis of disorders within the stomatognathic system.The second part was devoted to determine the validity and application of instrumental techniques in functional analysis in the diagnosis of disorders of the stomatognathic system and the impact assessment of silent jumps in joints on graphic records of abduction and adduction movements of the mandible. Material and methods. The study was conducted in a group of 55 people according to the methodology described in detail in the first part of the article. The results were analysed for the existence of statistical relationship (significance level at p <0.05) using Pearson’s Chi2 test – independence for bipartite tables between two qualitative variables. Results. The compared presence of transitions in the function of the temporomandibular joints with the records of abduction and adduction graphic tracks confirmed a significant correlation between these characteristics. In the group of 41 people showing the presence of these disorders the straight track was registered in only 5 of them, which makes less than 10% of all the surveyed. Conclusions. Electronic devices used to record jaw movements are a valuable instrument for supporting diagnostics, archiving and monitoring of therapy and patient education.

Dynamical quantum phase transitions in presence of a spin bath

We derive an effective time independent Hamiltonian for the transverse Ising model coupled to a spin bath, in the presence of a high frequency AC magnetic field. We show that the spin blocking mechanism that removes the quantum phase transition can be suppressed by the AC field, allowing high tunability of the quantum critical point. Finally, we calculate the phase diagram within the RPA approximation for the case of spin $7/2$ nuclei, appropriate to the $LiHo_{x}Y_{1-x}F_{4}$ system.

Phenazine Methosulphate Modulating the Expression of Genes Involved in Yeast to Hyphal Form Signal Transduction in <i>Candida albicans</i>

Candida albicans has ability to switch from yeast to hyphal form which is an important virulence factor. The objective of the research is to study the effect of Phenazine Methosulphate (PMS) on virulence factors and to study expression profile in yeast to hyphal form transition in C. albicans. Phenazine Methosulphate (PMS) acted as an inhibitor of yeast to hyphal form transition, adhesion and biofilm formation in C. albicans. RTPCR study demonstrated that PMS Modulate the expression of genes involved in Ras1-cAMP-Efg1 and Cek1-MAPK signal transduction pathways. Cell cycle of C. albicans was arrested at S phase on treatment of PMS. Hyphal suppressor genes like Tup1, Mig1 and Nrg1 were upregulated by PMS. Based on our data on expression of genes during yeast to hyphal form transition in presence and absence of PMS, we hypothesize that inhibition of hyphal formation may be due to the overexpression of negative regulators of hyphal growth. Targeting of hyphal specific genes involved in these pathways may be a promising strategy for anti-candida drug development.

In Ukrainian

The impact of electromagnetic fields on biological objects of various organization levels attracts specialists of different disciplines. At formation of the biological response to external physical effects, cell membranes play crucial role due to their ability to regulate biochemical processes in the cell, the possibility to change the rate of diffusion of ions and substrates and electronic structure of free radicals, orientation and other biological macromolecules. Citric acid is present in every act of microorganism’s vital activity as a key element of the cycle of tricarboxylic acids, and therefore plays an important role in the metabolism of living cells that use oxygen, and acts as accelerating and braking regulator of certain enzymatic processes of primary metabolism depending on the concentration. The active acidity significantly affects the vital activity in yeast. The purpose – to identify the patterns of influence of citric acid on yeast in suspension in the concentration range of 0–4 mg/ml, on vital processes of cells following the exposure of low electromagnetic radiation of millimeter range. The results of studies on the effect of citric acid (pH of the slurry) with different concentrations on exogenous and endogenous metabolism with the control of gas and heat during the life of yeast Saccharomyces cerevisiae, previously irradiated with low-intensity electromagnetic radiation of different frequencies of millimeters range are presented. It has been shown that low concentrations of citric acid (up to 2 mg/ml) inhibit the enzymatic process only at an initial stage and activate the processes of cell metabolism as both irradiated and nonirradiated. A substantial increase in the duration and thermal effect due to fermentation in the presence of citric acid indicates more complete assimilation of carbohydrates. The changing of the behavior of the relaxation curves for the systems containing citric acid indicates the presence of transition between stages of flooding and fermentation of such suspensions, which may be due to the restructuring plasmolemma of the cellular organism in self-defense against excessive concentration of citric acid in cells cytoplasm. The restructuring of the protein structural organization of plasmolemma requires additional energy costs and is recorded in the form of excess heat.

Floquet topological phases coupled to environments and the induced photocurrent

We consider the fate of a helical edge state of a spin Hall insulator and its topological transition in presence of a circularly polarized light when coupled to various forms of environments. A Lindblad type equation is developed to determine the fermion occupation of the Floquet bands. We find by using analytical and numerical methods that non-secular terms, corresponding to 2-photon transitions, lead to a mixing of the band occupations, hence the light induced photocurrent is in general not perfectly quantized in the presence of finite coupling to the environment, although deviations are small in the adiabatic limit. Sharp crossovers are identified at frequencies $\Omega$ and $\frac{1}{2}\Omega$ ($\Omega$ is the strength of light-matter coupling) with the former resembling to a phase transition.

Cholesterol–based Bisamides on Biphenyl Backbone: A Case of Selective Visual Sensing of F− and H2PO4− through Breaking and Making of Gels

AbstractCholesterol linked bisamides 1–3 on biphenyl spacers have been designed and synthesized. Compound 1 forms gel in CHCl3 – n‐hexane (1:6, v/v) solvent and the gel is selectively collapsed into sol in presence of F− with a color change from yellowish white to greenish yellow. Presence of pyridinium amides in 2 and 3 showed different gelation behaviours. While the chloride salt 2 displayed gelation in CHCl3 in presence of H2PO4−, compound 3 formed gel in DMSO: H2O (1:2, v/v) without having any assistance of externally added anion. The gel derived from 3 underwent rapid gel to sol transition in presence of H2PO4− and F− anions and validated their visual sensing.