A possible new phase of antagonistic nematogens in a disorienting field

A simple model is proposed for nematogenic molecules that favor perpendicular orientations as well as parallel ones. (Charged rods, for example, show this antagonistic tendency.) When a small disorienting field is applied along $z$, a low density phase $N_-$ of nematic order parameter $S_z<0$ coexists with a dense biaxial nematic $N_b$. (At zero field, $N_-$ becomes isotropic and $N_b$ uniaxial.) But at stronger fields, a new phase $N_{+4}$, invariant under $\pi/2$ rotations around the field axis, appears in between $N_-$ and $N_b$. Prospects for finding the $N_{+4}$ phase experimentally are briefly discussed.Comment: 4 pages, 2 figures. Accepted for publication in PR

Физика экологии сознания

It is considered the human health and the environment state in context of their mutual influence, interconnection and correspondence to the general natural laws.Рассматривается здоровье человека и состояние его среды обитания в контексте их взаимного влияния, взаимозависимости и соответствия общим законам природы

Annihilation of edge dislocations in smectic A liquid crystals

This paper presents a theoretical study of the annihilation of edge dislocations in the same smectic plane in a bulk smectic-A phase. We use a time-dependent Landau-Ginzburg approach where the smectic ordering is described by the complex order parameter psi( r--&gt; ,t) =eta e(iphi) . This quantity allows both the degree of layering and the position of the layers to be monitored. We are able to follow both precollision and postcollision regimes, and distinguish different early and late behaviors within these regimes. The early precollision regime is driven by changes in the phi ( r--&gt; ) configuration. The relative velocity of the defects is approximately inversely proportional to the interdefect separation distance. In the late precollision regime the symmetry changes within the cores of defects also become influential. Following the defect collision, in the early postcollision stage, bulk layer order is approached exponentially in time. At very late times, however, there seems to be a long-time power-law tail in the order parameter fluctuation relaxation

Topological Defects and Interactions in Nematic Emulsions

Inverse nematic emulsions in which surfactant-coated water droplets are dispersed in a nematic host fluid have distinctive properties that set them apart from dispersions of two isotropic fluids or of nematic droplets in an isotropic fluid. We present a comprehensive theoretical study of the distortions produced in the nematic host by the dispersed droplets and of solvent mediated dipolar interactions between droplets that lead to their experimentally observed chaining. A single droplet in a nematic host acts like a macroscopic hedgehog defect. Global boundary conditions force the nucleation of compensating topological defects in the nematic host. Using variational techniques, we show that in the lowest energy configuration, a single water droplet draws a single hedgehog out of the nematic host to form a tightly bound dipole. Configurations in which the water droplet is encircled by a disclination ring have higher energy. The droplet-dipole induces distortions in the nematic host that lead to an effective dipole-dipole interaction between droplets and hence to chaining.Comment: 17 double column pages prepared by RevTex, 15 eps figures included in text, 2 gif figures for Fig. 1

Parity Breaking in Nematic Tactoids

We theoretically investigate under what conditions the director field in a spindle-shaped nematic droplet or tactoid obtains a twisted, parity-broken structure. By minimizing the sum of the bulk elastic and surface energies, we show that a twisted director field is stable if the twist and bend elastic constants are small enough compared to the splay elastic constant, but only if the droplet volume is larger than some minimum value. We furthermore show that the transition from an untwisted to a twisted director-field structure is a sharp function of the various control parameters. We predict that suspensions of rigid, rod-like particles cannot support droplets with a parity broken structure, whereas they could possibly occur in those of semi-flexible, worm-like particles.Comment: 20 pages, 9 figures, submitted to Journal of Physics: Condensed Matte

Topology by Design in Magnetic nano-Materials: Artificial Spin Ice

Artificial Spin Ices are two dimensional arrays of magnetic, interacting nano-structures whose geometry can be chosen at will, and whose elementary degrees of freedom can be characterized directly. They were introduced at first to study frustration in a controllable setting, to mimic the behavior of spin ice rare earth pyrochlores, but at more useful temperature and field ranges and with direct characterization, and to provide practical implementation to celebrated, exactly solvable models of statistical mechanics previously devised to gain an understanding of degenerate ensembles with residual entropy. With the evolution of nano--fabrication and of experimental protocols it is now possible to characterize the material in real-time, real-space, and to realize virtually any geometry, for direct control over the collective dynamics. This has recently opened a path toward the deliberate design of novel, exotic states, not found in natural materials, and often characterized by topological properties. Without any pretense of exhaustiveness, we will provide an introduction to the material, the early works, and then, by reporting on more recent results, we will proceed to describe the new direction, which includes the design of desired topological states and their implications to kinetics.Comment: 29 pages, 13 figures, 116 references, Book Chapte

Endoskeletal structure in Cheirolepis (Osteichthyes, Actinopterygii), An early ray-finned fish

As the sister lineage of all other actinopterygians, the Middle to Late Devonian (Eifelian–Frasnian) Cheirolepis occupies a pivotal position in vertebrate phylogeny. Although the dermal skeleton of this taxon has been exhaustively described, very little of its endoskeleton is known, leaving questions of neurocranial and fin evolution in early ray‐finned fishes unresolved. The model for early actinopterygian anatomy has instead been based largely on the Late Devonian (Frasnian) Mimipiscis, preserved in stunning detail from the Gogo Formation of Australia. Here, we present re‐examinations of existing museum specimens through the use of high‐resolution laboratory‐ and synchrotron‐based computed tomography scanning, revealing new details of the neuro‐cranium, hyomandibula and pectoral fin endoskeleton for the Eifelian Cheirolepis trailli. These new data highlight traits considered uncharacteristic of early actinopterygians, including an uninvested dorsal aorta and imperforate propterygium, and corroborate the early divergence of Cheirolepis within actinopterygian phylogeny. These traits represent conspicuous differences between the endoskeletal structure of Cheirolepis and Mimipiscis. Additionally, we describe new aspects of the parasphenoid, vomer and scales, most notably that the scales display peg‐and‐socket articulation and a distinct neck. Collectively, these new data help clarify primitive conditions within ray‐finned fishes, which in turn have important implications for understanding features likely present in the last common ancestor of living osteichthyans

Sustainable Ecology of the Metropolis and a Local Green Frame Involving Beneficial Insects on the Example of St. Petersburg

The article describes the results of design studies aimed at increasing the sustainability of the environment by attracting beneficial insects in the structure of the formation of a green frame. The work was carried out in 2021-2023, the vector of design research was formed on the basis of the St. Petersburg State University of Architecture and Civil Engineering (SPbGASU) undergraduate program and continues in the format of networking, including with the participation of Sevastopol State University (SevSU) undergraduate program ” directions “Landscape architecture”. The article describes both landscape and ideological practices that help attract beneficial insects to the territory of landscape objects, and also describes specific solutions on the example of the territory of the Petrogradsky and Kirovsky districts of the city of St. Petersburg, made with the participation of residents and the Improvement Committee. The importance of insects in the urban green network is described, the possibility of integrating special landscape zones into green infrastructure for this, the problem of creating a single ecological frame of the metropolis and a local green frame at the district level is considered. The author’s design methodology is presented in terms of the transition from the urban and town-planning level to specific design solutions at the masterplan level and, further, to the development of specific landscape niches with the landscaping species composition

Annihilation of edge dislocations in smectic A liquid crystals

This paper presents a theoretical study of the annihilation of edge dislocations in the same smectic plane in a bulk smectic-A phase. We use a time-dependent Landau-Ginzburg approach where the smectic ordering is described by the complex order parameter psi( r--&gt; ,t) =eta e(iphi) . This quantity allows both the degree of layering and the position of the layers to be monitored. We are able to follow both precollision and postcollision regimes, and distinguish different early and late behaviors within these regimes. The early precollision regime is driven by changes in the phi ( r--&gt; ) configuration. The relative velocity of the defects is approximately inversely proportional to the interdefect separation distance. In the late precollision regime the symmetry changes within the cores of defects also become influential. Following the defect collision, in the early postcollision stage, bulk layer order is approached exponentially in time. At very late times, however, there seems to be a long-time power-law tail in the order parameter fluctuation relaxation

Морфологічні зміни тканини простати хворих на доброякісну гіперплазію передміхурової залози внаслідок модифікованої вапоризації лазером «Dornier Medilas D UroBeam».

The results of morphological ivestigation of prostate tissue after vaporization prostatectomy by «Dornier Medilas D UroBeam» laser and transurethral prostate resection in patients with benigh prostatic hyperplasia is shown. We found that the successive use laser «Dornier Medilas D Urobeam» at power 175-250 W and transurethral resectionof prostate provides diminishing of area of coagulative necrosis which prevents formation of massive scab. At the same time the photoselective to haemoglobin as a result of vaporization draws coagulative necrosis of content of vessels in areas with unchanged stroma and prevents bleeding.Представлены результаты морфологического исследования тканей простаты, полученных при использовании комбинации двух методов – вапоризации лазером«DornierMedilasDUroBeam» и трансуретральной резекции простаты – у пациентов с доброкачественной гиперплазией предстательной железы. Установлено, что последовательное использование вапоризации лазером «DornierMedilasDUroBeam» при мощности 175-250 Вт и трансуретральной резекции обеспечивает уменьшение зоны коагуляционного некроза , что препятствует образованию массивного струпа, а фотоселективность лазерного излучения к гемоглобіну вызывает коагуляционный некроз содержимого сосудов в очагах с неизмененной стромой, что препятствует кровотечению.Представлені результати морфологічного дослідження тканин простати, отриманих при використанні комбінації двох методів – вапоризації лазером «Dornier Medilas D UroBeam» і трансуретральної резекції простати у пацієнтів з доброякісною гіперплазією передміхурової залози. Встановлено, що послідовне використання вапоризації лазером «Dornier Medilas D UroBeam» при потужності 175-250 Вт та трансуретральної резекції забезпечує зменшення зони коагуляційного некрозу, що запобігає утворенню масивного струпа, а фотоселективність лазерного випромінювання до гемоглобіну спричиняє коагуляційний некроз вмісту судин у ділянках з незміненою стромою, що запобігає кровотечі