Investigation of formation and applications of high-speed liquid projectiles

The work comprises experimental and numerical studies of generation and application of high-speed liquid projectiles. Numerical models were created for a projectile formation by two kinds of launchers, water extruder and water cannon. In the water extruder the kinetic energy of a fast moving piston is transferred to the water load and extrudes the load at a high speed. By contrast in the water cannon the water load itself accumulates the kinetic energy from the expanding combustion gasses. Then, in the course of water motion through the converging nozzle the energy is redistributed between head and tail of the projectile. This enables us to accelerate the front part of the water load to extremely high velocity which may exceed the speed of sound in the water. Inviscid, quasi-stationary model of water flow in the extruder was applied for investigation of the projectile generation in the water extruder. Unsteady 1 -D compressible and incompressible models of water flow in the water cannon were applied for the process investigation. Comparison of the result of application of compressible and incompressible models demonstrated that fluid compressibility and subsequently wave processes in the fluid do not contribute for the fluid acceleration. Thus, the acceleration is due to redistribution of the fluid momentum between different parts of a projectile. The numerical study also demonstrated the feasibility to attain the supersonic velocity in the course of acceleration in a converging nozzle. Of course this phenomenon is possible only for unsteady processes. An experimental technique was developed and applied for online measurement of the projectile head velocity. The acquired experimental data validated the developed numerical technique. Because the attainment the velocity of 1750m/s was shown experimentally, while the sound speed in the water is 1500m/s, the possibility to reach the supersonic velocity in a converging nozzle was demonstrated experimentally. The constructed numerical model was integrated into the Nelder-Mead simplex search optimization procedure provided by Matlab and used for evaluation of an optimal parameter of a launcher. Particularly, the possibility of the improvement of the nozzle design was shown. Feasibility of material processing and explosive setups neutralization with high-speed liquid projectiles was studied experimentally using a water extruder and a water cannon. The series of experiments were carried out to evaluate peculiarities of deformation of ductile and brittle materials in the course of high-speed liquid impact. It was shown that while the depth of penetration into a ductile material is monotonously decreasing with increase of stand-off distance, the effect of stand-off distance onto penetration of brittle material has an extremal character. A series of experiments were carried out in order to investigate the demolition of brittle, deformation of ductile and neutralization of explosive material by the use of high-speed liquid projectile. The feasibility of the development of novel impact-based construction, manufacturing and demining technology based on the use of high-speed liquid projectiles was demonstrated

External agency: Redefinition of ex ante value in agency relationships

In this dissertation, in response to mixed empirical findings and theoretical criticism of Agency Theory, I raise a broader question: are there agency behaviors that are not considered within traditional renderings of Agency Theory? I argue that, because agents vary in their mobility, human market imperfections and their ex ante costs do not disappear with creation of a contract and cannot be assumed away. These costs are constantly redefined and must be included in the general model of agency that I develop. I define certain behaviors that are ex ante driven to be external agency behaviors.In this dissertation I define five aspects of agent mobility that facilitate ex ante driven external agency: 1) availability of alternative contracts; 2) heterogeneity in general human capital; 3) heterogeneity in social capital; 4) heterogeneity in agent's charisma; and 5) outcome measurability. I develop a theoretical model of how agent mobility moderates the fundamental theoretical relationships in Agency Theory and develop a set of hypotheses to test my arguments.The results of this dissertation provide support for the conceptualization of agent's mobility as a previously unexplored alignment mechanism in the agency relationship that lowers the downside risk of the agent and can enhance the alignment of risk preferences and goals between the agent and the principal. I find support for the existence of ex ante agency costs that are associated with the expansion of market for contracts via diversification. The results also provide evidence to the costs of agent's mobility in terms of higher increases in total compensation for more mobile agents

An Ising model on a 3D honeycomb zigzag-ladder lattice : a solution to the ground-state problem

A complex, seven-parameter ground-state problem for an Ising model on a 3D honeycomb zigzag-ladder lattice, containing two types of magnetic sites, is considered in the presence of an external field using the method of basic rays and basic sets of cluster configurations. It is shown that the geometrical frustration due to the presence of triangle elements leads to the emergence of a large variety of magnetic phases, the majority of which are highly degenerate. The obtained theoretical results are used to elucidate the sequence of phase transitions in the family of rare-earth oxides with a honeycomb zigzag-ladder lattice. New phases predicted by our model and observed experimentally do not appear in previously considered simpler models for noninteracting zigzag-ladders

Dispersionless spin waves and underlying field-induced magnetic order in gadolinium gallium garnet

We report the results of neutron diffraction and inelastic neutron scattering on a powder sample of Gd3Ga5O12 at high magnetic fields. Analysis of the diffraction data shows that in high fields (B ≳ 1.8 T) the spins are not fully aligned, but are canted slightly as a result of the dipolar interaction. The magnetic phase for fields ≲1.8 T is characterized by antiferromagnetic peaks at (210) and an incommensurate wave vector. The dominant contribution to inelastic scattering at large momentum transfers is from a band of almost dispersionless excitations. We show that these correspond to the spin waves localized on ten site rings, expected on the basis of nearest neighbor exchange interaction, and that the spectrum at high fields B ≳ 1.8 T is well described by a spin wave theory

LiHoF4_4: Cuboidal Demagnetizing Factor in an Ising Ferromagnet

The demagnetizing factor has an important effect on the physics of ferromagnets. For cuboidal samples it depends on susceptibility and the historic problem of determining this function continues to generate theoretical and experimental challenges. To test a recent theory, we measure the magnetic susceptibility of the Ising dipolar ferromagnet LiHoF$_4$, using samples of varying aspect ratio, and we reconsider the demagnetizing transformation necessary to obtain the intrinsic material susceptibility. Our experimental results confirm that the microscopic details of the material significantly affect the transformation, as predicted. In particular, we find that the uniaxial Ising spins require a demagnetizing transformation that differs from the one needed for Heisenberg spins and that use of the wrong demagnetizing transformation would result in unacceptably large errors in the measured physical properties of the system. Our results further shed light on the origin of the mysterious `flat' susceptibility of ordered ferromagnets by demonstrating that the intrinsic susceptibility of the ordered ferromagnetic phase is infinite, regardless of sample shape.Comment: 8 pages, 4 figure

Spin correlations in Ca3Co2O6: A polarised-neutron diffraction and Monte Carlo study

We present polarised-neutron diffraction measurements of the Ising-like spin-chain compound Ca3Co2O6 above and below the magnetic ordering temperature TN. Below TN, a clear evolution from a single-phase spin-density wave (SDW) structure to a mixture of SDW and commensurate antiferromagnet (CAFM) structures is observed on cooling. For a rapidly-cooled sample, the majority phase at low temperature is the SDW, while if the cooling is performed sufficiently slowly, then the SDW and the CAFM structure coexist between 1.5 and 10 K. Above TN, we use Monte Carlo methods to analyse the magnetic diffuse scattering data. We show that both intra- and inter-chain correlations persist above TN, but are essentially decoupled. Intra-chain correlations resemble the ferromagnetic Ising model, while inter-chain correlations resemble the frustrated triangular-lattice antiferromagnet. Using previously-published bulk property measurements and our neutron diffraction data, we obtain values of the ferromagnetic and antiferromagnetic exchange interactions and the single-ion anisotropy.Comment: 10 pages, 7 figure

Field-induced magnetic states in holmium tetraboride

A study of the zero field and field induced magnetic states of the frustrated rare earth tetraboride HoB4 has been carried out using single crystal neutron diffraction complemented by magnetization measurements. In zero field, HoB4 shows magnetic phase transitions at TN1 = 7.1 K to an incommensurate state with a propagation vector (delta, delta, delta'), where delta = 0.02 and delta' = 0.43 and at TN2 = 5.7 K to a noncollinear commensurate antiferromagnetic structure. Polarized neutron diffraction measurements in zero field have revealed that the incommensurate reflections, albeit much reduced in intensity, persist down to 1.5 K despite antiferromagnetic ordering at 5.7 K. At lower temperatures, application of a magnetic field along the c axis initially re-establishes the incommensurate phase as the dominant magnetic state in a narrow field range, just prior to HoB4 ordering with an up-up-down ferrimagnetic structure characterized by the (h k 1/3)-type reflections between 18 and 24 kOe. This field range is marked by the previously reported M/M-sat = 1 3 magnetization plateau, which we also see in our magnetization measurements. The region between 21 and 33 kOe is characterized by the increase in the intensity of the antiferromagnetic reflections, such as (100), the maximum of which coincides with the appearance of the narrow magnetization plateau with M/M-sat approximate to 3/5. Further increase of the magnetic field results in the stabilization of a polarized state above 33 kOe, while the incommensurate reflections are clearly present in all fields up to 59 kOe. We propose the H-T phase diagram of HoB4 for the H parallel to c containing both stationary and transitionary magnetic phases which overlap and show significant history dependence

Колективна травма населення України: реалії, перспективи та можливість дослідження трансгенераційного аспекту

Introduction. Ukraine is experiencing a great upheaval - a large-scale war. This distressing situation affects the entire population of the country, therefore, beyond any doubt, the term "collective traumatization" can be used for today's situation in Ukraine. Modern research and study of the impact of collective trauma in Ukraine refers to the analysis of its negative consequences on various spheres of life, including the sphere of mental health: identification of the level of anxiety, psychological consequences, symptoms of posttraumatic stress disorders. Although, the study of the impact of a powerful collective trauma on future generations Ukrainians needs timely planning and preparation. The aim of study: to conduct a theoretical analysis of approaches to the study of the concept of "collective trauma", to study the concept of memory in the understanding of collective trauma, to analyze the peredictors and preventors of transgenerational transmission of collective trauma, to consider the epigenetic mechanisms of collective trauma, to investigate the research psychometric tools on the transmission of transgenerational trauma between generations, to investigate the specifics of the collective trauma of the population of Ukraine. Method. A literature search was conducted in the scientific databases of Web of Science, Scopus, Pub Med, Google Scholar using the keywords "collective trauma", "traumatic memory", "transgenerational trauma", "cultural trauma", "multigenerational legacies of trauma" in the period from 2002 to 2023. 17,720 sources were identified. Inclusion criteria were: (a) controlled randomized research (b) on preventors and predictors of transmission of collective trauma (c) to subsequent generations. The results. 46 international publications were included in the literature review, and predictors and preventers of the transmission of trauma through generations were analyzed from the standpoint of attachment theory, family systems, and epigenetics. Most authors note the presence of a link between the parents' trauma and the mental health of the offspring, the greater intensity of the reparative adaptive styles the greater is the risk of developing affective or anxiety disorders in the offspring. The studies of epigenetic mechanisms of the transgenerational impact of trauma have shown the presence of changes in the methylation of the FKMB-5 gene in Holocaust survivors and their descendants. The collective trauma experienced by the people of Ukraine at the times of war has its own specificity, which distinguishes it from other collective traumas, including those experienced directly by the Ukrainian people in the past (the Holodomor, the Second World War, the Holocaust, the disaster at the Chernobyl Nuclear Power Plant). In order to further conduct research and study the transmission of war trauma in Ukraine through subsequent generations and to identify possible factors of resistance, the "Danieli Inventory of Multigenerational legacies of trauma" was adapted for the Ukrainian context of war (Appendix 1). Conclusions. Research on a topic of multigenerational legacies of collective trauma is a debatable issue. Research on factors of transgenetic changes in large groups in Ukraine is needed. Research on the next generations should include (a) large-scale genetic studies, (b) analysis on plevalence and distribution of mental health disorders in children of war veterans and the survivors of collective trauma, (c) changes in social behavior of the new generations. Вступ. Україна переживає велике потрясіння під назвою широкомасштабна війна. Ця дистресова ситуація впливає на все населення країни, тому поза всяким сумнівом до сьогоднішньої ситуації в Україні можна вживати термін «колективна травматизація». Сучасні дослідження та вивчення впливу колективної травми в Україні відносяться до аналізу її негативних наслідків на різні сфери життя, в тому числі і  сферу психічного здоров’я: визначення рівня тривоги, психологічних наслідків, ознак постстресових розладів, проте дослідження впливу потужної колективної травми на наступні покоління українців потребує вчасного планування та підготовки. Мета: здійснити теоретичний аналіз підходів до дослідження поняття «колективна травма», вивчити концепції пам’яті в розумінні колективної травми, проаналізувати предиктори та превентори трансгенераційної передачі колективної травми, розглянути епігенетичні механізми колективної травми, дослідити та адаптувати інструментарій дослідження передачі трансгенераційної травми між поколіннями, дослідити специфіку колективної травми населення України. Метод. Був проведений пошук літератури у наукометричних базах пошуку Web of Science, Scopus, Pub Med, Google Scholar за ключовими словами  «колективна травна», «травматична пам’ять», «collective trauma», «transgenerational trauma», «cultural trauma», «multigenerational legacies of trauma». В період з 2002 по 2023 рік. Було виявлено 17720 джерел, до огляду літератури були включені публікації, що містили інформацію про (а) контрольовані дослідження  (б) превенторів та предикторів передачі колективної травми  (в) наступним поколінням.  Результати. В огляд літератури було включено 46 міжнародних публікацій, були проаналізовані предиктори та превентори передачі травми крізь покоління з позиції теорії прив’язаності, сімейних систем та епігенетики. Більшість авторів відмічають наявність зв’язку між травмою батьків та психічним здоров’ям нащадків, більша інтенсивність репаративних адаптаційних впливів батьків підвищує ризик розвитку афективних або тривожних розладів в нащадків. Доказовим стало вивчення епігенетичних механізмів трансгенераційного впливу травми, дослідженнями показали наявність змін метилування гену FKMB-5 у виживших Голокосту та їх нащадків. Колективна травма, яку переживає в цей час народ України, має свою специфіку, що відрізняє її від інших колективних травм, в тому числі і пережитих безпосередньо українським народом раніше (наприклад: Голодомор, Друга світова війна, Голокост, катастрофа на Чорнобильській Атомній Станції).З метою подальшого проведення дослідження та вивчення передачі травми війни в Україні крізь наступні покоління та виявлення можливих факторів стійкості була адаптована «Анкета Я. Данієлі: Передача травматичного досвіду крізь покоління» (Додаток 1). Висновки. Колективна травма, а зокрема, її трансгенераційна передача, є дискусійним та актуальним питанням у сучасному світі. В Україні потребують подальшого дослідження фактори трансгенетичних змін великих груп людей. Дослідження в наступних поколіннях повинні включати (а) широкомасштабні генетичні дослідження, (б) аналіз захворюваності дітей ветеранів війни та населення, яке пережило колективні травми, (в) особливості соціальної поведінки нового покоління. &nbsp

Reducing Disorder in Artificial Kagome Ice

Artificial spin ice has become a valuable tool for understanding magnetic interactions on a microscopic level. The strength in the approach lies in the ability of a synthetic array of nanoscale magnets to mimic crystalline materials, composed of atomic magnetic moments. Unfortunately, these nanoscale magnets, patterned from metal alloys, can show substantial variation in relevant quantities such as coercive field, with deviations up to 6%. By carefully studying the reversal process of artificial kagome ice, we can directly measure the distribution of coercivities, and by switching from disconnected islands to a connected structure, we find that the coercivity distribution can achieve a deviation of only 3.3%. These narrow deviations should allow the observation of behavior that mimics canonical spin-ice materials more closely