Constant Problem Research Articles

UKRAINIAN HISTORIANS IN THE INTERWAR POLAND: PARTICIPATION IN INTERNATIONAL SCIENTIFIC ACTIVITY

The purpose of the article is to comprehensively investigate the forms and directions of international activity of Ukrainian historians of interwar Poland based on the analysis of various historiographical literature. The research methodology relies on the use of an interdisciplinary approach. Based on the principles of objectivity and historicism, the research has d the structural-functional systematic analysis of historiographical facts and the comparative-historical method. The article has used the heuristic possibilities of periodisation, classification and typology methods. The scientific novelty of the article consists in an attempt to comprehensively reconstruct the participation of Ukrainian historians of interwar Poland in international scientific cooperation. Conclusions. Despite the generally repressive cultural policies of the Polish government, Ukrainian historians in the Second Polish Republic generally adapted well to the difficult political and financial circumstances. Giving a proper response to numerous socio-political and cultural challenges, they managed to preserve the traditions formed at the turn of the 19th and 20th centuries. Mainly traditions of international scientific cooperation and, despite constant financial problems, Ukrainian free socio-humanitarianism in foreign forums. In terms of institutions, international scientific cooperation was most actively established by the members of the Shevchenko Scientific Society and the Ukrainian Scientific Institute in Warsaw. This cultural activity gained special national importance in the 1930s of the 20th century, when Ukrainian socio-humanitarianism was subjected to devastating repression under the Soviet occupation. In general, in the conditions of stateless existence at the time, the international scientific cooperation developed by Ukrainian historians in the Second Polish Republic was a kind of cultural diplomacy, realizing the important task of establishing the political subjectivity of Ukrainians.

Cosmology in Minkowski space

Theoretical and observational challenges to standard cosmology such as the cosmological constant problem and tensions between cosmological model parameters inferred from different observations motivate the development and search of new physics. A less radical approach to venturing beyond the standard model is the simple mathematical reformulation of our theoretical frameworks underlying it. While leaving physical measurements unaffected, this can offer a reinterpretation and even solutions of these problems. In this spirit, metric transformations are performed here that cast our Universe into different geometries. Of particular interest thereby is the formulation of cosmology in Minkowski space. Rather than an expansion of space, spatial curvature, and small-scale inhomogeneities and anisotropies, this frame exhibits a variation of mass, length and time scales across spacetime. Alternatively, this may be interpreted as an evolution of fundamental constants. As applications of this reframed cosmological picture, the naturalness of the cosmological constant is reinspected and promising candidates of geometric origin are explored for dark matter, dark energy, inflation and baryogenesis. An immediate observation thereby is the apparent absence of the cosmological constant problem in the Minkowski frame. The formalism is also applied to identify new observable signatures of conformal inhomogeneities, which have been proposed as simultaneous solution of the observational tensions in the Hubble constant, the amplitude of matter fluctuations, and the gravitational lensing amplitude of cosmic microwave background anisotropies. These are found to enhance redshifts to distant galaxy clusters and introduce a mass bias with cluster masses inferred from gravitational lensing exceeding those inferred kinematically or dynamically.

Numerical radius inequalities and estimation of zeros of polynomials

Abstract Let A be a bounded linear operator defined on a complex Hilbert space and let | A | = ( A * ⁢ A ) 1 2 {|A|=(A^{*}A)^{\frac{1}{2}}} . Among other refinements of the well-known numerical radius inequality w 2 ⁢ ( A ) ≤ 1 2 ⁢ ∥ A * ⁢ A + A ⁢ A * ∥ {w^{2}(A)\leq\frac{1}{2}\|A^{*}A+AA^{*}\|} , we show that w 2 ⁢ ( A ) ≤ 1 4 ⁢ w 2 ⁢ ( | A ⁢ | + i | ⁢ A * | ) + 1 8 ⁢ ∥ | A | 2 + | A * | 2 ∥ + 1 4 ⁢ w ⁢ ( | A | ⁢ | A * | ) ≤ 1 2 ⁢ ∥ A * ⁢ A + A ⁢ A * ∥ . w^{2}(A)\leq\frac{1}{4}w^{2}(|A|+{\rm i}|A^{*}|)+\frac{1}{8}\||A|^{2}+|A^{*}|^% {2}\|+\frac{1}{4}w(|A||A^{*}|)\leq\frac{1}{2}\|A^{*}A+AA^{*}\|. Also, we develop inequalities involving the numerical radius and the spectral radius for the sum of the product operators, from which we derive the inequalities w p ⁢ ( A ) ≤ 1 2 ⁢ w ⁢ ( | A | p + i ⁢ | A * | p ) ≤ ∥ A ∥ p w^{p}(A)\leq\frac{1}{\sqrt{2}}w(|A|^{p}+{\rm i}|A^{*}|^{p})\leq\|A\|^{p} for all p ≥ 1 {p\geq 1} . Further, we derive new bounds for the zeros of complex polynomials.

Total stability of equilibria motivates integral action in discrete-time nonlinear systems

Robustness guarantees are important properties to be looked for during control design. They ensure stability of closed-loop systems in face of uncertainties, unmodeled effects and bounded disturbances. Inspired by the continuous-time literature, in this article we investigate the total stability properties of dynamical discrete-time nonlinear systems. Such a property locally relates phase plots of dynamical systems of the same dimension which are “similar enough”. As a consequence, it enables the analysis of robustness properties via simple model difference in the discrete-time context. First, we study how existence of equilibria for a nominal model transfers to sufficiently similar ones. Then, we provide results on the propagation of stability guarantees to perturbed systems. Finally, we relate such properties to the constant output regulation problem by motivating the use of discrete-time integral action in discrete-time nonlinear systems for model robustness purposes.

On de Sitter spacetime and string theory

We review various aspects of de Sitter spacetime in string theory: its status as an Effective Field Theory spacetime solution, its relation to the vacuum energy problem in string theory, its (global) holographic definition in terms of two entangled and noncanonical conformal field theories as well as a realization of a realistic de Sitter universe endowed with the observed visible matter and the necessary dark sector in order to reproduce the realistic cosmological structure. In particular, based on the new insight regarding the cosmological constant problem in string theory, we argue that in a doubled, [Formula: see text]-duality-symmetric, phase-space-like and noncommutative generalized-geometric formulation, string theory can naturally lead to a small and positive cosmological constant that is radiatively stable and technically natural. Such a formulation is fundamentally based on a quantum spacetime, but in an effective spacetime description of this general formulation of string theory, the curvature of the dual spacetime is the cosmological constant of the observed spacetime, while the size of the dual spacetime is the gravitational constant of the same observed spacetime. Also, the three scales associated with intrinsic noncommutativity of string theory, the cosmological constant scale, the Planck scale as well as the Higgs scale, can be arranged to satisfy various seesaw-like formulae. Along the way, we show that these new features of string theory can be implemented in a particular deformation of cosmic-string-like models.

Emergent Diffeomorphism Invariance in Toy Models

AbstractConceptual difficulties in semiclassical and quantum gravity arise from diffeomorphism invariance of classical general relativity. With a motivation to shed some light on these difficulties, a class of toy models for which one‐dimensional diffeomorphism invariance, namely time‐reparametrization invariance, emerges at the classical level from energy conservation are studied. An attempt to quantize the models while taking the invariance seriously leads to toy versions of the problem of time in quantum gravity, of the cosmological constant problem, and of the black hole firewall problem. Nevertheless, all these problems are easily resolved by taking into account that the invariance emerges only at the classical level, while the fundamental theory that needs to be quantized is not diffeomorphism invariant.

Spacetime as a Complex Network and the Cosmological Constant Problem

We propose a promising model of discrete spacetime based on nonassociative geometry and complex networks. Our approach treats space as a simplicial 3-complex (or complex network), built from “atoms” of spacetime and entangled states forming n-dimensional simplices (n=1,2,3). At large scales, a highly connected network is a coarse, discrete representation of a smooth spacetime. We show that, for high temperatures, the network describes disconnected discrete space. At the Planck temperature, the system experiences phase transition, and for low temperatures, the space becomes a triangulated discrete space. We show that the cosmological constant depends on the Universe’s topology. The “foamy” structure, analogous to Wheeler’s “spacetime foam”, significantly contributes to the effective cosmological constant, which is determined by the Euler characteristic of the Universe.

How to deal with missing data? Multiple imputation by chained equations: recommendations and explanations for clinical practice

The presence of missing data, a constant problem in medical research, has several consequences: systematic loss of power, associated or not with a reduction in the representativeness of the sample analyzed. There are three types of missing data: 1) missing completely at random (MCAR); 2) missing at random (MAR); 3) missing not at random (MNAR). Multiple imputation by chained equations allows for the correct handling of missing data under the MCAR and MAR assumptions. It allows to simulate for each missing data j, a number m of simulated values which seem plausible with regard to the other variables. A random effect is included in this simulation to express the uncertainty. Several data sets are thus created and analyzed individually, in an identical way. Then the estimators of each data set are combined to obtain a global estimator. Multiple imputation increases power, corrects for some biases and has the advantage of being applicable to many types of variables. Complete case analysis should no longer be the norm. The objective of this guide is to help the reader in conducting an analysis with multiple imputed data. We cover the following points: the different types of missing data, the different historical approaches to handling them, and then we detail the multiple imputation method using chained equations. We provide a code example for the mice package of R®.

3D Content Encryption Using Multi-Level Chaotic Maps

Nowadays, 3D content is becoming an essential part of multimedia applications, when the 3D content is not protected, hackers may attack and steal it. This paper introduces a proposed scheme that provides high protection for 3D content by implementing multiple levels of security with preserving the original size using weight factor (w). First level of security is implemented by encrypting the texture map based on a 2D Logistic chaotic map. Second level is implemented by shuffling vertices (confusion) based on a 1D Tent chaotic map. Third level is implemented by modifying the vertices values (diffusion) based on a 3D Lorenz chaotic map. Results illustrate that the proposed scheme is completely deform the entire 3D content according to Hausdorff Distance (HD) approximately around 100 after the encryption process. It provides a high security against brute force attack because it has large key space equal to 10165 and secret key sensitivity using NPCR near 99:6% and UACI near 33:4%. The histogram and HD indicate the decrypted 3D content is identical to the origin where HD values approximate zero.

Why there is something rather than nothing: A proposal for the cosmological constant problem

This work is based on the idea that the observed cosmological constant is preferred for a stable vacuum, where a running gravitational coupling is considered. The most probable value of the cosmological constant is determined by the minimum of the vacuum energy density, and it is just proportional to the matter density. When the cosmological constant is connected with a modified dispersion relation (MDR) via an effective Newton constant, it may impose a constraint on the latter: the exponent of the leading correction should be n = 3.

Mingling of the infrared and ultraviolet and the “cosmological constant” for interacting QFT in 2d

We propose a proper definition of the vacuum expectation value of the stress energy tensor 〈0| Tμν| 0〉 for integrable quantum field theories in two spacetime dimensions, which is the analog of the cosmological constant in 4d. For a wide variety of models, massive or massless, we show {rho}_{textrm{vac}}=-{m}^2/2mathfrak{g} exactly, where mathfrak{g} is a generalized coupling which we compute and m is a basic mass scale. The kinds of models we consider are the massive sinh-Gordon and sine-Gordon theories and perturbations of the Yang-Lee and 3-state Potts models, pure Toverline{T} perturbations of infra-red QFT’s, and UV completions of the latter which are massless flows between UV and IR fixed points. In the massive case m is the physical mass of the lightest particle and mathfrak{g} is related to parameters in the 2-body S-matrix. In some examples ρvac = 0 due to a fractional supersymmetry. For massless cases, m can be a scale of spontaneous symmetry breaking. The “cosmological constant problem” generically arises in the free field limit mathfrak{g} → 0, thus interactions can potentially resolve the problem at least for most cases considered in this paper. We speculate on extensions of these results to 4 spacetime dimensions and propose {rho}_{textrm{vac}}={m}^4/2mathfrak{g} , however without integrability we cannot yet propose a precise manner in which to calculate mathfrak{g} . Nevertheless, based on cosmological data on ρvac, if mathfrak{g} ~ 1 then it is worth pointing out that the lightest mass particle is on the order of experimental values of proposed neutrino masses.

New approach to unimodular relativity

A thorough study and analysis on the conceptual foundations of unimodular gravity shows that this theory is essentially general relativity disguised as unimodular relativity in the literature. The main reason for this dilemma is accepting the Einsteinian paradigm: general relativistic framework, covariant divergence law for matter energy-momentum tensor, and cosmological constant as an integration constant, but introducing the artefact of unimodular description absent in Einstein’s work. A new approach is proposed in this paper in which pure unimodular relativity is defined in terms of equi-projective geodesics with the fundamental metric tensor having determinant unity and the geometric tensors constructed from them. Modification of covariant divergence law for the matter energy-momentum tensor is shown to have two new consequences. In the conventional unimodular gravity an effective cosmological term comprising of two variable scalar fields, namely, the unimodular geometric ambiguity and unimodular matter energy ambiguity, is proposed. A radical departure on the cosmological constant problem is possible assuming differing evolution of the two scalars: the Einstein equations emerge when the two ambiguities cancel each other. Secondly, in the case of pure unimodular relativity the gravitational field equations are proposed consistent with the unimodular space-time structure.

Time-symmetric quantization of relativistic fields. 1. Complex fields, massless gauge fields and gravitons

In the standard formulation of quantum field theory (QFT), where there are only positive energy particles and antiparticles, the energy and charge of the vacuum diverge, which, due to the existence of gravity, leads to the inconsistency of the theory (cosmological constant problem). In the article, it is shown that in the Stueckelberg-Feynman (SF) interpretation, where antiparticles are described as negative energy particles moving backward in time, the zero-point energy and zero-point charge of vacuum of complex fields are absent and there is no cosmological constant problem. However, until now it was believed that the SF interpretation leads to negative probabilities and incompatible with QFT. In the article, it is presented a new formulation of QFT on the basis of the SF interpretation in the form of time-symmetric quantization (TSQ), where the probability of states is positive. In TSQ, the consequences of the SF interpretation are taken into account consecutively and it is shown that: a) the negative sign of the norm of states only changes the sign of the wave function, and not the probabilities; b) the expression of backward in time integrals through the forward in time integrals changes sign; c) the time ordering of the operators is symmetric in time and writing them through the usual ordering leads to the standard diagram technique. For this reason, TSQ correctly describes the known observable effects. In TSQ, the results of unification models change, in particular, a) there is no zero-point energy even with broken supersymmetry between complex fields; b) there is no zero-point energy of modes in string theories, which allows to include gravity, but there is no a conformal anomaly and the dimension of space can be arbitrary.

Investment support of the agrarian sector of the economy of Ukraine in the pre-war and post-war periods

The article is devoted to the analysis of trends and shifts in the investment provision of the agrarian sector. The approaches of various scientists regarding the essence of the concept of "investment security" have been analyzed. It is established that it includes not only the forms, methods, levers and tools of investment support, but also their division into tools for investment forecasting, investment attraction and distribution, investment regulation and tools for evaluating the effectiveness/ efficiency of investment implementation. This allows you to reasonably choose the method of resource provision and ensure a comprehensive approach to solving the issue of investing in the agricultural sector. The contribution of the agricultural sector to the creation of the country's gross domestic product was assessed and it was established that the current level is insufficient for achieving strategic goals and solving current problems. An important indicator of the investment process is the gross accumulation of fixed capital in the structure of the national GDP. It was established that Ukraine has a level almost twice as low as this indicator and belongs to the last group of underdeveloped countries. This shows that the deficit of capital investments for the agricultural sector was and is a constant problem. It has been proven that direct investments grew until 2013, and then fell sharply due to the annexation of Crimea and the occupation of Donbas and fluctuated in a "narrow corridor", but at the same time, in primary production - it decreased by half, and in the food industry - it increased by a third. With the transfer of DI reporting from the State Statistics Service to the NBU in 2020, the methodology of their calculation also changed, which made it impossible to analyze the dynamics of direct investment over different periods of time. It was established that the main source of investment in primary production was and is the own funds of enterprises and organizations, which are strengthened by bank loans, and in some years supplemented by funds from the state and local budgets. Regarding the national economy, the list is wider: funds of the population for the construction of their own apartments, loans from foreign banks, funds of foreign investors and domestic investment companies, funds, etc. When investing in material assets, the key positions are occupied by capital investments in machines and equipment (3/5-3/4), but significantly less (1/6-1/4) in the construction and reconstruction of buildings, which allows modernization of production. The division of enterprises into separate groups according to the principle of attracting capital investments more/less than by primary production/food industry is systematized. Different types of enterprises have been obtained, depending on the gaps between their own capabilities and the volume of capital investments financed by them, which are covered by external borrowings. The direct and indirect losses inflicted on the agricultural sector from Russian aggression are generalized and the key risks for its functioning are systematized. The main principles of the Plan for the Revival of Ukraine were revealed and the projects under the "New Agrarian Policy" direction, which have already begun to be implemented, were systematized. It was established that the volume of capital investments for their implementation in the average annual calculation is almost three times higher than the corresponding for the last five reporting years in primary production. Key words: capital and direct investments, primary production, food industry, directions of investment, direct and indirect losses, economic potential of the industry.

Effect of high calorie formula on head circumference and body length on young children with stunted due to feeding problems

Background: Feeding is a complex process which requires the coordination of several organ systems. However, special conditions lead to feeding problems which increase risk of nutrition problems and growth retardation, resulting in undernutrition. Objectives: This study was performed to investigate young children's length and head circumference. More specifically, this study investigated children stunted due to feeding problems in their first two years and with over three months of nutritional and medicative intervention. Methods: A cross-sectional study was conducted from January 2019-December 2020 on healthy young children. These children were aged 6 to 24 months and brought in by their parents for nutritional consultations due to constant body weight or feeding problems. Subject numbers were determined using total sampling during the study period. The feeding problem diagnosis and physical examination were done by a pediatrician specialized in nutrition and metabolic syndromes. Results: There were 139 infants and young children recruited, of which 65 were boys and 74 were girls. Their mean age was 15.11, give or take 0.53 months. There were 32 subjects selected based on their experience with at least three months of nutritional intervention and medication. Microcephaly was detected in three subjects (23.08%). Nutritional intervention increased the head circumference-for-age z-score (HCAZ) from -0.77 + 1.19 to -0.27 + 1.05 (p = 0.012). After 90 days of intervention, there was no microcephaly detected despite no significant difference. Nutritional intervention also increased the height-for-age z-score. Conclusion: Feeding problems contributes to constant body weight gain and feeding problems. Nutritional intervention can be done by giving children high calorie formula to prevent growth faltering and restore growth during the first two years of life. Nutritional intervention improved the growth parameters, including head circumference z-scores.

Asymptotic stabilization of a transformed quadrotor model using energy-shaping method: Theory and experiments

This note presents a new passivity-based controller that ensures asymptotic stability for quadrotor position without solving partial differential equations or performing a partial dynamic inversion. After a resourceful change of coordinates, a pre-feedback controller, and a backstepping stage on the yaw angle dynamic, it is possible to identify new quadrotor cyclo passive outputs. Then, a simple proportional-integral controller of these cyclo-passive outputs completes the design. The cyclo-passive outputs allow the construction of an energy-based Lyapunov function that includes five out of six quadrotor degrees of freedom and guarantees asymptotic stability of the desired equilibrium. Moreover, the constant velocity reference tracking problem is solved with a slight modification to the proposed controller. Finally, the approach is validated through simulations and real-time experimental results.

Emergent gravity from the IIB matrix model and cancellation of a cosmological constant

We review a cosmological model where the metric determinant plays a dynamical role and present new numerical results on the cancellation of the vacuum energy density including the contribution of a cosmological constant. The action of this model is only invariant under restricted coordinate transformations with unit Jacobian (the same restriction appears in the well-known unimodular-gravity approach to the cosmological constant problem). As to the possible origin of the nonstandard terms in the matter action of the model, we show that these terms can, in principle, arise from the emergent gravity in the IIB matrix model, a nonperturbative formulation of superstring theory.

Theoretical and Numerical Constant Mean Curvature Surface and Liquid Entry Pressure Calculations for a Combined Pillar–Pore Structure

Modern microfabrication techniques have led to a growing interest in micropillars and pillar–pore structures. Therefore, in this paper a study of the liquid entry pressure of a hydrophobic pillar–pore structure and the corresponding liquid–gas interface shape for the pressurized liquid is presented. We theoretically analysed the constant mean curvature problem for the rotationally symmetric case and determined an analytical expression for the liquid entry pressure of a hydrophobic pillar–pore structure. Furthermore, the shape of the liquid–gas interface as well as a formula for the location of the minimum were derived. The results are useful for designing geometries with specific properties, such as preventing or facilitating liquid intrusion into rough structures. We compared these results to multiphase lattice Boltzmann simulations where equilibrium contact angles in the range of 157∘ to 102∘ were tested. In our further analysis, we compared theoretical findings from previous works to our lattice Boltzmann simulations. The presented cases can serve as a benchmark for the development and validation of numerical multiphase models.

Alleviating the cosmological constant problem from particle production

We explore a toy model mechanism of geometric cancellation, alleviating the (classical) cosmological constant problem. To do so, we assume at primordial times that vacuum energy fuels an inflationary quadratic hilltop potential nonminimally coupled to gravity through a standard Yukawa-like interacting term, whose background lies on a perturbed Friedmann–Robertson–Walker metric. We demonstrate how vacuum energy release transforms into geometric particles, adopting a quasi-de Sitter phase where we compute the expected particle density and mass ranges. Perturbations are introduced by means of the usual external-field approximation, so that the back-reaction of the created particles on the geometry is not considered here. We discuss the limitations of this approach and we also suggest possible refinements. We then propose the most suitable dark matter candidates, showing under which circumstances we can interpret dark matter as constituted by geometric quasiparticles. We confront our predictions with quantum particle production and constraints made using a Higgs portal. In addition, the role of the bare cosmological constant is reinterpreted to speed up the Universe today. Thus, consequences on the standard ΛCDM paradigm are critically highlighted, showing how both coincidence and fine-tuning issues can be healed requiring the Israel–Darmois matching conditions between our involved inhomogeneous and homogeneous phases.

Functional outcome of Hirschsprung's disease in children: A single center study at The Children's Hospital Lahore.

Hirschsprung's disease (HD) is a congenital bowel disorder resulting in functional dysmotility. Advancement in surgical techniques has improved outcomes, but recent studies have identified problems having significant impact on patient's quality of life. The aim of this study is to analyze postoperative functional outcome after definitive surgery for Hirschsprung's disease. A retrospective study was conducted at the Department of Pediatric Surgery, The Children's Hospital Lahore. The record of 64 patients was reviewed from the year 2009 to 2019. Parents were interviewed on phone calls and a predesigned questionnaire was filled. Degree of constipation, incontinence and voluntary bowel movements was analyzed according to Krickenbeck classification. Median age at initial presentation was 11days, with male to female ratio of 3.9:1. Most common presentation was delayed passage of meconium (38%). Diagnosis was made on biopsy in 70.3%, but contrast enema and biopsy in 29.7%. Aganglionosis was limited to short segment in 81.3% and long segment in 14.5%. Decompressing enterostomy was made in 63% at a mean age of 191days. Definitive surgery included Duhamel pull-through in 89.1%. Mean age at follow-up was 10.6 ± 4.19years and alive patients were 95.4%. Postoperative enterocolitis was reported by 27%, while 35.5% reported fecal incontinence and 16.1% complained of constipation.80% could voluntarilyhold bowel movement, among which 5% had a feeling of urge and 15% had the capacity to verbalize. In 25% of thepatients, fecal incontinence was a constant social problem and in 25% of these patients constipation was resistant to diet and laxatives. On long-term follow-up, fecal incontinence was more worrisome, affecting quality of life and requiring help of the bowel management program. Such patients need close follow-up after definitive procedure, so that they have normal stooling habits in their adulthood and lead a normal life.