Strong Phase Research Articles

Controllable strain-driven topological phase transition and dominant surface-state transport in HfTe5

The fine-tuning of topologically protected states in quantum materials holds great promise for novel electronic devices. However, there are limited methods that allow for the controlled and efficient modulation of the crystal lattice while simultaneously monitoring the changes in the electronic structure within a single sample. Here, we apply significant and controllable strain to high-quality HfTe5 samples and perform electrical transport measurements to reveal the topological phase transition from a weak topological insulator phase to a strong topological insulator phase. After applying high strain to HfTe5 and converting it into a strong topological insulator, we found that the resistivity of the sample increased by 190,500% and that the electronic transport was dominated by the topological surface states at cryogenic temperatures. Our results demonstrate the suitability of HfTe5 as a material for engineering topological properties, with the potential to generalize this approach to study topological phase transitions in van der Waals materials and heterostructures.

DIFFERENT-SCALE HETEROGENEITIES IN SEGMENTS OF SEISMOGENIC FAULTS AND THEIR INFLUENCE ON SLIP MODES

The paper presents some multidisciplinary research results on the structure of slip surfaces in segmented sections of tectonic faults in the Baikal region and Mongolia. The properties of subsurface (modern) and deep slip planes that came to the earth’s surface as a result of many-kilometer denudation in the upper part of the earth’s crust are studied at different levels-from macroscale to nanocrystals. Other types of heterogeneities characterizing the structure of fault slip zones are also considered. The presented data indicate a heterogeneous structure of tectonic faults. Their slip zones show both low friction in sections where strong mineral phases are replaced by weak minerals, and potentially unstable patches with high frictional resistance. The results obtained in a comprehensive study of geological conditions, under which different-scale heterogeneities emerge in exhumed fault segments, should be taken into account when developing rock mass models suitable for numerical simulation of earthquake preparation processes at the micro-, mesoand macroscales.

Imaging the retinal and choroidal vasculature using Spatio-Temporal Optical Coherence Tomography (STOC-T)

Spatio-Temporal Optical Coherence Tomography (STOC-T) is a novel imaging technique using light with controlled spatial and temporal coherence. Retinal images obtained using the STOC-T system maintain high resolution in all three dimensions, on a sample of about 700 μm, without the need for mechanical scanning. In the present work, we use known data processing algorithms for optical coherence tomography angiography (OCTA) and modify them to improve the rendering of the vasculature in the human retina at different depths by introducing the angio STOC-T method. The algorithms are primarily sensitive to the strong signal phase variance corresponding to the appearance of a wide Doppler band in STOC-T signals obtained for millisecond exposure times. After using STOC-T angiography, we can render high contrast images of the choroid.

All-pass phase shifting achieved by acoustic unidirectional guided resonances

Phase manipulation of sound is an important function for many acoustic applications. Here, we apply temporal coupled mode theory to demonstrate that sound all-pass phase shifting, which means that acoustic waves propagate with unit amplitude but have strong phase changes, can be achieved by utilizing acoustic unidirectional guided resonances (AUGRs). An oblique layered acoustic structure with inversion-symmetry is proposed to realize AUGRs that radiate only to one side of the structure. Full-wave simulations are employed to validate the theoretical analysis. With the strong phase-only resonances, our proposed acoustic structure can find applications in acoustic filtering and sensing.

High Precision Coulometry and Calorimetry Measurements of Side Reactions for Si/NCA and G/NMC811 Cells

Side reactions taking place at both anode and cathode can be investigated via different methods. Common methods include the high precision coulometry [1-3] and the isothermal calorimetry [4, 5]. In this study, pure silicon anode (70 wt%) Si/NCA cells and pure graphite G/NMC811 cells are investigated via the methods mentioned above. These measurements include voltage holds and charge and discharge endpoint slippage analysis, which is described in [6]. Glazier et al. [4] already showed that after sufficient time, the heat flow during a voltage hold is equivalent to the side reactions taking place. The aim of this study is to investigate the dependency of side reaction currents and parasitic heat on different voltages and temperatures. In addition, their behaviour during the transient phase caused via relaxation processes and edge effects [7] comparing silicon and graphite materials.The cells voltage was held at different state-of-charge (SOC) conditions, low, medium, and high as well as at different temperatures. At the beginning and at the end of the experiment, check-ups were performed to compare the capacity loss and to analyse the endpoint slippage. During the measurements, the heat flow and the leakage current of the cells were measured simultaneously.The preliminary results show that for the low and for the high SOCs, a strong opposing transient phase is present at the beginning of the voltage hold. The strong transient phase is expected for silicon-based materials due to their high relaxation characteristics, meaning also higher leakage currents for this material. Additionally, it was found that the different pre-histories of the cells influence the amount of leakage current measured. Meaning that the actual side reaction current is only achieved after edge effects and relaxation processes cease, which can take a long time for pure Si anodes, up to 1000 hours at 25°C. Moreover, the transient phase of the thermal and the electrical signals was correlated for the different materials.The study of side reactions for lithium ion cells is investigated in the project “ExZellTUM III”, funded by the German Federal Ministry of Education and Research (BMBF) under grant number 03XP0255. [1] Smith, A.; Burns, J.; Dahn, J.: A high precision study of the coulombic efficiency of Li-ion batteries, In: Electrochemical and Solid-State Letters 13, pp. A177, 2010 [2] Smith, A.; Burns, J.; Xiong, D.; Dahn, J.: Interpreting High Precision Coulometry Results on Li-ion Cells, In: Journal of The Electrochemical Society 158, S. A1136– A1142, 2011 [3] Burns, J. C.; Jain, G.; Smith, A. J.; Eberman, K. W.; Scott, E.; Gardner, J. P.; Dahn, J. R.: Evaluation of effects of additives in wound Li-ion cells through high precision coulometry, In: Journal of The Electrochemical Society, 158 (3), A255-A261, 2011 [4] Glazier, S. L.; Downie, L. E.; Xia, J.; Louli, A. J.; Dahn, J. R.: Effects of fluorinated carbonate solvent blends on high voltage parasitic reactions in lithium ion cells using OCV isothermal microcalorimetry, In: Journal of The Electrochemical Society, 163 (10), A2131-A2138, 2016 [5] Glazier, S. L.; Odom, S. A.; Kaur, A. P.; Dahn, J. R.: Determining parasitic reaction enthalpies in lithium-ion cells using isothermal microcalorimetry, In: Journal of The Electrochemical Society, 165 (14), A3449-A3458, 2018 [6] Streck, L.; Roth, T.; Keil, P.; Strehle, B.; Ludmann, S.; Jossen, A.: A comparison of voltage hold and voltage decay methods for side reactions characterization, In: Journal of The Electrochemical Society, 170, 040520, 2023 [7] Roth, T.; Streck, L.; Graule, A.; Niehoff, P.; Jossen, A.: Relaxation effects in self-discharge measurements of lithium-ion batteries, In: Journal of The Electrochemical Society, 170, 020502, 2023

Design, synthesis, and molecular docking of novel 1,3, 4-triaryl pyrazole derivatives bearing methylsulfonyl moiety with anticancer activity through dual targeting CDK2 and COX-2 enzymes

Novel 3-(4-methylsulfonylphenyl) pyrazole derivatives with different substitutions at position four were designed, synthesized, characterized by spectroscopic techniques, and investigated as potential anticancer agents via inhibition of cyclin-dependent kinase 2 and cyclooxygenase-2 enzymes. All the synthesized compounds were screened against three cancer cell line panels, hepatocellular carcinoma (HepG-2), mammary gland breast cancer (MCF-7), and colorectal carcinoma (HCT-116), to determine their antiproliferative properties by MTT assay. Compounds 5a, 6a, 6c, and 10c exhibited a considerable antiproliferative effect on HepG-2 cell line with IC50 value of 2.88 to 8.57 µM, on HCT-116 cell line with IC50 value of 6.34 to 17.84 µM, and on MCF-7 cell line with IC50 value of 1.75 to 9.58 µM. Compounds 5a, 6a, 6c, and 10c had weak toxicity towards normal HEK-293T, especially 10c displayed the highest IC50 with a value of 101.21 μM against normal cells. Furthermore, mechanistic studies for the antiproliferative activity were performed on the most active compounds 5a, 6a, 6c, and 10c. Compound 6c exhibited significant inhibitory activity against CDK2 enzyme with IC50 value of 0.614 µM compared to R-roscovitine (IC50 = 0.533 µM) as a reference drug. Additionally, compounds 5a, 6a, 6c, and 10c have significant potency and selectivity for the COX-2 enzyme (IC50 = 0.058 – 0.089 µM) over COX-1 enzyme (IC50 = 9.7 – 11.6 µM) compared to celecoxib and indomethacin. Accordingly, compounds 5a and 6c showed potent COX-2 inhibitory activity with IC50 values of 0.058 and 0.075 µM with a selectivity index of 198.27 and 154.66, respectively, in comparison to celecoxib and indomethacin with COX-2 IC50 value of 0.046 and 0.079 µM and a selectivity index of 315.21 and 1.25. compound 6c, with the potent CDK2 and COX-2 inhibitory activity, demonstrated apoptotic activity on HepG-2 cancer cells by inducing a strong G1 phase cell cycle arrest. Also, compound 6c significantly elevated the Bax/Bcl-2 ratio by 14.54 folds compared to the untreated control, which is clearly correlated with its sensitivity to apoptosis. Molecular docking and dynamics simulations were conducted to illustrate the binding modes inside the active sites. Finally, the hit compound 6c was discovered to have antiproliferative activity against HepG-2, MCF-7, and HCT-116 cancer cell lines by inhibiting CDK2 and COX-2 enzymes as proposal mechanisms.

Magnetogenesis in a Collisionless Plasma: From Weibel Instability to Turbulent Dynamo

We report on a first-principles numerical and theoretical study of plasma dynamo in a fully kinetic framework. By applying an external mechanical force to an initially unmagnetized plasma, we develop a self-consistent treatment of the generation of “seed” magnetic fields, the formation of turbulence, and the inductive amplification of fields by the fluctuation dynamo. Driven large-scale motions in an unmagnetized, weakly collisional plasma are subject to strong phase mixing, which leads to the development of thermal pressure anisotropy. This anisotropy triggers the Weibel instability, which produces filamentary “seed” magnetic fields on plasma-kinetic scales. The plasma is thereby magnetized, enabling efficient stretching and folding of the fields by the plasma motions and the development of Larmor-scale kinetic instabilities such as the firehose and mirror. The scattering of particles off the associated microscale magnetic fluctuations provides an effective viscosity, regulating the field morphology and turbulence. During this process, the seed field is further amplified by the fluctuation dynamo until energy equipartition with the turbulent flow is reached. By demonstrating that equipartition magnetic fields can be generated from an initially unmagnetized plasma through large-scale turbulent flows, this work has important implications for the origin and amplification of magnetic fields in the intracluster and intergalactic mediums.

3D tomographic phase retrieval and unwrapping

This paper develops uniqueness theory for 3D phase retrieval with finite, discrete measurement data for strong phase objects and weak phase objects, including: (i) Unique determination of (phase) projections from diffraction patterns—General measurement schemes with coded and uncoded apertures are proposed and shown to ensure unique reduction of diffraction patterns to the phase projection for a strong phase object (respectively, the projection for a weak phase object) in each direction separately without the knowledge of relative orientations and locations. (ii) Uniqueness for 3D phase unwrapping—General conditions for unique determination of a 3D strong phase object from its phase projection data are established, including, but not limited to, random tilt schemes densely sampled from a spherical triangle of vertexes in three orthogonal directions and other deterministic tilt schemes. (iii) Uniqueness for projection tomography—Unique determination of an object of n 3 voxels from generic n projections or n + 1 coded diffraction patterns is proved. This approach of reducing 3D phase retrieval to the problem of (phase) projection tomography has the practical implication of enabling classification and alignment, when relative orientations are unknown, to be carried out in terms of (phase) projections, instead of diffraction patterns. The applications with the measurement schemes such as single-axis tilt, conical tilt, dual-axis tilt, random conical tilt and general random tilt are discussed.

Synergistic formulation approach for developing pea protein and guar gum enriched olive oil-in-water emulsion gels as solid fat substitutes: Formulation optimization, characterization, and molecular simulation

This study aimed to optimize the formulation of olive oil-in-water (O/W) emulsion gels by incorporating Pea Protein (PP) and Guar Gum (GG) as alternative options for solid fats. The optimum rheological (consistency index, apparent viscosity, recovery) and texture (firmness) properties of the emulsion gels were obtained using a mixture of 2 % PP, 1 % GG, 60 % Olive Oil (OO), and 37 % Water (W). The blend of PP2/GG1 showed the highest results for recovery and firmness, 111.27 % and 33.89 g, respectively. PP/GG blend emulsion gels exhibited higher absolute ζ-potential values, ranging between −72.3 and −77.4 mV. The polydispersity index (PDI) ranged from 0.185 to 0.535, with the most uniform distributions found in the PP/GG blend emulsion gels. Strong phase separation resistance indicated strong stability of PP-GG complex emulsion gels. Higher PP concentrations decreased emulsion oxidation. FTIR and XRD research showed that PP and GG interact strongly, indicating good compatibility. The free binding energy of the most stable configuration of the molecules was −6.8 kcal mol−1, indicating a high affinity. PP interacted with GG through 9 amino acid residues, with notable residues being Asp 224, Thr 235, Ala 332, Ile 334, and Arg 336, and their respective interaction distances ranged between 2.69 Å and 3.87 Å.

Novel refractory high-entropy metal-ceramic composites with superior mechanical properties

A new concept of refractory high-entropy metal-ceramic composites (HEMCC) has been proposed that combines the outstanding physical properties of both high-entropy alloy (HEA) and high-entropy ceramic (HEC). As the first HEMCC system, to the best of our knowledge, TiTaNbZr-(TiTaNbZr)C, has been developed by a powder metallurgy process. The HEA and HEC phases exhibit body-centered cubic (BCC) and rock-salt B1 crystal structures, respectively, and both phases have non-equimolar chemical compositions. With the increase of the HEC phase in HEMCC, the hardness is enhanced while the density and fracture toughness are decreased. HEA50C sintered from 50 vol% HEA and 50 vol% HEC precursor powders shows a favorable combination of flexural strength (541 ± 48 MPa) and fracture toughness (6.93 ± 0.27 MPa·m1/2) at room temperature and a high compressive strength at 1300 °C (275 MPa). The optimized mechanical performance of HEMCC might be attributed to the combination of the ductile HEA and strong HEC phases, smaller grain size, and crack arrest at HEC/HEA interfaces.

Experimental Determination of the Ionospheric Effects and Cycle Slip Phenomena for Galileo and GPS in the Arctic

The ionosphere can impair the accuracy, availability and reliability of satellite-based positioning, navigation and timing. The Arctic region is particularly affected by strong ionospheric gradients and phase scintillation, posing a safety issue for critical infrastructure and operations. Ionospheric warning and impact maps can provide support to Arctic operations, but to produce such maps threshold values have to be determined. This study investigates how such thresholds can be derived from the GPS and Galileo satellite signals. Rapid changes in total electron content (TEC) or scintillation-induced receiver tracking errors could result in cycle slips or even loss of lock. Cycle slips and data outages are used as a measure of impact on the receiver in this paper. For Galileo, 73.6% of the impacts were cycle slips and 26.4% were outages, while for GPS, 29.3% of the impacts were cycle slips and 70.7% were outages. Considering the sum of cycle slips and outages, it is worth noting that the sum of impacts for Galileo signals is larger than for GPS. A range of possible explanations have been examined through hardware-in-the-loop simulations. The simulations showed that the GPS L2 signal was not adequately tracked during rapid TEC changes and TEC changes were underestimated, thus the GPS cycle slips, derived from L1 and L2 derived TEC changes, were not all registered. These results are important in designing threshold values for TEC and for scintillation impact maps as well as for the operation of GNSS equipment in the Arctic. In particular, the results show that ionospheric changes could be underestimated if GPS L1 and L2 were used in isolation from other dual frequency combinations. It is the first time this analysis has been made for Greenland and the first time that the dual frequency derivation of ionospheric delay using GPS L1 and L2 has been shown to underestimate large TEC gradients. This has important implications for informing GNSS operations that rely on GPS to provide reliable estimates of the ionosphere.

Сорбционно-структурные свойства аэрогельных материалов на основе биополимеров

Nowadays aerogel materials (AM) are successfully used as entero- and applicative sorbents to eliminate excessive amounts of heavy metals and toxins from living organisms. Natural biopolymers alginate and chitosan, as well as various lignin derivatives are an inexhaustible raw material base for the creation of AM. A significant number of sorption materials and wound coatings of various types have been developed on their basis, which is associated not only with a wide range of physicochemical properties of these polymers and their already proven biomedical activity, but also with the prevalence and renewability of raw material sources for the production of these polymers, ease of extraction, the possibility of achieving a high degree of purification and relatively low price. The key stage in the AM synthesis is the formation of a strong hydrogel which is the AM framework. One of the technological methods is to obtain interpolyelectrolyte solid hydrogel. The paper proposes two different packaging models for the formation of the structure of interpolyelectrolyte complexes (IPEC) based on biopolymers pairs: sodium alginate (ALNa)–chitosan (CT) and sodium lignosulfonate (LSNa)–CT. The first model is a block model, in which the structure is formed due to ionic bonds between the carboxyl groups of ALNa and amino groups of CT, as well as a cooperative system of hydrogen bonds and dispersion interactions. The second model is an aggregation-tubular model, the structure of which is formed through ionic bonds between sulfogroups (within the rod-shaped supramolecular structures of LSNa) and amino groups of CT, as well as hydrogen bonds and dispersion interactions. Upon the process of IPEC drying under supercritical (SC-) conditions, strong phase contacts are formed, and the changes in the gel structure become irreversible. As a result, hydrophobic micro- and mesoporous two-component AMs differing in internal structure were obtained. AM ALNa–CT are characterized by fibrillar structure, and LSNa–CT – by structural elements of spherical shape. The obtained AM ALNa–CT and LSNa–CT have high sorption activity towards water and a wide range of heavy metals and low molecular weight toxins. The purpose of the work is to study the structural and sorption properties of AM based on biopolymers of various structural organization. A significant increase in the sorption activity of AM ALNa–CT in comparison with LSNa–CT is apparently due to their different supramolecular structure. There is a combination of several sorption mechanisms such as wetting, absorption, diffusion, osmotic phenomena and chemical interaction due to the highly porous structure of AM and the presence of sorption-active centers. For citation: Brovko O.S., Palamarchuk I.A., Gorshkova N.A., Bogdanovich N.I., Ivakhnov A.D. Sorption and Structural Properties of Aerogel Materials Based on Biopolymers. Lesnoy Zhurnal = Russian Forestry Journal, 2023, no. 6, pp. 190–203. (In Russ.). https://doi.org/10.37482/0536-1036-2023-6-190-203

High-Q and modulation-depth PIT-like effect through the phase coupling between guided modes and Tamm state in a hybrid Tamm plasmon system

High-quality (high-Q) resonators play a crucial role in optical-wave manipulation. It is challenging to excite guide modes in 1-D photonic crystals (PhC guided modes (PCGMs)) because of their high Q factors and complex patterns. To address this, a hybrid cavity Tamm plasmon (HCTP) structure composed of a metal film, cavity, and 1-D photonic crystal (1-D PhC) was designed. Subsequently, a grating was incorporated into the HCTP structure to diffract the electric fields of the HCTP resonance mode. This efficiently excited the PCGMs. When the detuning between the PCGM and HCTP modes approached zero, a plasmon-induced transparency (PIT)-like effect occurred. Under normal incidence, the PIT-like effect exhibited an impressively high Q factor (5015.5). The physical properties of the PIT-like effect were analyzed using the coupling mode theory. The results show that there is a strong phase coupling between PCGM and HCTP modes. This resulted in a modulation depth of 97.4 %. Under an oblique incidence, the degenerated PCGMs split into two modes. Both these were coupled with the HCTP mode. This resulted in a double PIT-like effect with a high modulation depth. The Q factor was enhanced further to 8957.7. Active modulation of the PIT-like spectra was achieved by modifying the incident or polarization angle. The coupling also exhibited slow-light properties, with a group delay of 17.54 ps under inclined incidence. The strong coupling between PCGM and HCTP resulted in the generation of high-Q and deep-modulation PIT-like effect. These hold high potential for various applications such as nanosensing, slow-light devices, nanolasers, and angle detectors.

Higher orders for cosmological phase transitions: a global study in a Yukawa model

We perform a state-of-the-art global study of the cosmological thermal histories of a simple Yukawa model, and find higher perturbative orders to be important for determining both the presence and strength of strong first-order phase transitions. Using high-temperature effective field theory, we calculate the free energy density of the model up to O\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\mathcal{O} $$\\end{document}(y5T4), where y is the Yukawa coupling and T is the temperature. The locations of phase transitions are found using the results of lattice Monte-Carlo simulations, and the strength of first-order transitions are evaluated within perturbation theory, to 3-loop order. This is the first global study of any model at this order. Compared to a vanilla 1-loop analysis, accurate to O\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\mathcal{O} $$\\end{document}(y2T4), reaching such accuracy enables on average a five-fold reduction in the relative uncertainty in the predicted critical temperature Tc, and an additional ∼ 50% strong first-order transitions with latent heat L/Tc4\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ L/{T}_c^4 $$\\end{document}> 0.1 to be identified in our scan.

Probing electroweak phase transition in the singlet Standard Model via bbγγ and 4l channels

We investigate the prospects for resonant di-Higgs and heavy Higgs production searches at the 14 TeV HL-LHC in the combination of bbγγ and 4l channels, as a probe of a possible first order electroweak phase transition in real singlet scalar extension of the Standard Model. Event selection follows those utilized in the bbγγ and 4l searches by the ATLAS Collaboration, applied to simulation using benchmark parameters that realize a strong first order electroweak phase transition. The output of discriminant analysis is implemented by numerical calculation, optimised by the joint restriction from the two channels. The prospective reach for bbγγ/4l channel could be more competitive in probing the electroweak phase transition at lower/higher resonance masses. With 3 ab−1 integrated luminosity, the combination of the bbγγ and 4l channels can discover/exclude a significant portion of the viable parameter space that realizes a strong first order phase transition when the resonance mass is heavier than 500 GeV.

Demonstrating more than 2π phase modulation in non-Hermitian asymmetric multilayers

Phase modulation has come to be recognized as a fundamental paradigm for optical device design in applications involving the spatiotemporal control of optical wavefronts. Here, the cavities use a combination of absorptive and lossless layers with ideal conductive metal to control reflection and phase shift, similar to the Fabry–Pérot system, which has zero reflection and perfect transmission. Multilayers with different sequences and composed of several stack layers were examined for reflectivity when activated in a prism-coupled layout. The layer’s different arrangements, resulting in open and closed asymmetric multilayers, display reflectance spectra with distinct features as well as phase and shifts. In the open configuration, there is a strong coupling between the hybridized resonance mode and the exciton from the red dye. As a result, energy-based topological considerations identify a correlation between exciton/polariton strong coupling, topological darkness, and phase tuning, and they motivate the phase shift range.

Stellar-wind variability in Cygnus X-1 from high-resolution excess variance spectroscopy with Chandra

Context. Stellar winds of massive stars are known to be driven by line absorption of UV photons, a mechanism that is prone to instabilities, causing the wind to be clumpy. The clumpy structure hampers wind mass-loss estimates, limiting our understanding of massive star evolution. The wind structure also impacts accretion in high-mass X-ray binary (HMXB) systems. Aims. We aim to analyse the wavelength-dependent variability of X-ray absorption in the wind to study its structure. Such an approach is possible in HMXBs, where the compact object serves as an X-ray backlight. We probe different parts of the wind by analysing data taken at superior and inferior conjunctions. Methods. We applied excess variance spectroscopy to study the wavelength-dependent soft (2–14 Å) X-ray variability of the HMXB Cygnus X-1 in the hard spectral state. Excess variance spectroscopy quantifies the variability of an object above the statistical noise as a function of wavelength, which allows us to study the variability of individual spectral lines. This technique was applied to high-resolution gratings spectra provided by Chandra, accounting for various systematic effects. The frequency dependence is investigated by changing the time binning. Results. The strong orbital phase dependence we observe in the excess variance is consistent with column-density variations predicted by a simple model for a clumpy wind. We identify spikes of increased variability with spectral features found by previous spectroscopic analyses of the same data set, most notably from silicon in over-dense clumps in the wind. In the silicon line region, the variability power is redistributed towards lower frequencies, hinting at increased line variability in large clumps. In prospect of the microcalorimetry missions that are scheduled to launch within the next decade, excess variance spectra present a promising approach to constraining the wind structure, especially if accompanied by models that consider changing ionisation.

Exploring topological phase transition in Pt2Hg1−xTlxSe3

The transition from trivial to non-trivial phase in two-dimensional materials are called a topological phase transition (TPT). The Berry phase, non-local string order parameter, and edge states define the topological nature of the system. A newly discovered jacutingaite ma- terial Pt2HgSe3 is a layered material which occurs naturally in the form of minerals. The material can be exfoliated and was predicted as a quantum spin Hall insulator. Here, on the basis of density functional theory and tight-binding calculations, we explore Pt2Hg1−xTlxSe3 (x = 0.25, 0.50, 0.75, 1) to understand the electronic and topological properties. We start with the parent material Pt2HgSe3 wherein Hg is replaced partially with x amount of Tl, to tune the topological phases. From the electronic structure calculations, Pt2HgSe3 is found to be a non-trivial semimetal in it’s bulk. Upon electron doping, the material transforms to strong topological metallic phase. The topological Z2 invariant calculation shows TPT in Pt2Hg1−xTlxSe3 with weak topological insulating state (0;001) for x=0, to strong topological metal (1;000) for x=1, respectively.

Efecto de las fluctuaciones del nivel hidrométrico sobre el fitoplancton en tres lagunas isleñas en el área de la confluencia de los ríos Paraná y Paraguay

.The phytoplankton of three island ponds (Los Pájaros, Catay and Turbia) (27°25’S; 58°45’W) in the begening of Paraná river floodplain were studied. These ponds are periodically flooded by the river. Catay pond was in pennanent contact with the riverwhile the other two were flooded during high water periods.Sampling was carried out during 1978-1980. Cell counts were madeby the U termohl method. Population density and diversity and were analyzed. Cell density were comparatively highest (1733, 2084 and 1028 ind. ml4 in Pájaros, Catay and Turbiaponds, respectively) either when hydrometric level was slowly increasing or after small flood phases. On the contrary, cell density were lowest in coincidence with strong flooding phases (83,73 and 57 ind. mi'1, respectively). Catay pond, the one which is in pennanent contact with the river showed highest both population density and diversity. During high water periods strong similarity ainong three ponds were observed.In Pájaros and Catay ponds Chlorophyceae (Monoraphidium, Schroederia and Scenedesmus), Ciyptophyceae (Cryp tomonas spp.) and Diatomophyceae A ulacoseira granúlala) were dominant. In the Turbia pond Euglenophyceae (Traclielomonasvolvocina) and Cryptophyceae (Cryptomonas spp.) were dominant.Nannoplankton represented between 60 and 90% of the total in all the studied ponds.

On structural organisation and crystallisation/vitrification phenomena in low molecular weight glass-forming liquid crystals

ABSTRACT Results of the dielectric spectroscopy, differrential scaning calorimetry, adiabatic calorimetry, X-ray diffraction and infrared spectroscopy studies concerning the formation of glasses with some degrees of long-range order and the cold crystallisation phenomenon in about 15 liquid crystal compounds are discussed. Based on the temperature dependence of molecular dynamics, the liquid-like N, N*, SmC* and SmC*A phases have been identified as the fragile glass formers, while the solid-like SmI*A, SmBcr, SmE and SmG phases and the orientationally disordered and conformationally disordered crystals as the strong ones. Features of cold crystallisation in the fragile and strong glass-forming phases are presented. A comparison of cold and melt crystallisations is made. The role of molecular chains in the stability of liquid crystal phases is emphasised. We also discuss the quasi-binary model of the liquid crystal order in the smectics.