Occurrence Of Singularities Research Articles

Quaternion-based non-singular nonlinear impact angle guidance for three-dimensional engagements

This paper proposes a three-dimensional impact angle-constrained nonlinear guidance strategy against different types of targets. To avoid the occurrence of singularities, in Euler angle-based approaches, the development of this guidance strategy is solely based on quaternion dynamics. An explicit relationship between the quaternions representing impact orientation and line-of-sight orientation at the time of collision is derived. Based on the obtained relation, a guidance law is derived using a sliding mode control technique to track the desired line-of-sight orientation for target interception. The performance of the proposed guidance strategy is evaluated for constant-speed and different time-varying-speed interceptor models accounting for the effect of varying aerodynamic parameters on interceptor speed. The numerical simulations performed show satisfactory results for all engagements, validating the efficacy and robustness of the proposed guidance law.

First record of the West Atlantic Ariopsis felis (Linnaeus, 1766) (Actinopterygii: Siluriformes: Ariidae) in the Mediterranean Sea

A single individual of Ariidae was captured in 2022 in the Palestinian waters off the Gaza Strip, eastern Mediterranean. A comprehensive description of the morphological and meristic characters of the specimen was conducted. Molecular identification was performed through sequence analysis of the Cytochrome Oxidase subunit I (COI). The specimen was identified as Ariopsis felis, both morphologically and genetically. The natural range of this species is the western Atlantic and, to the best of our knowledge, the species has never been reported before from Mediterranean waters. The singular occurrence of this fish in the basin prompts further discussion, raising questions about the possible vectors that may be responsible for this new introduction in the Mediterranean Sea.

MANAGEMENT OF AORTIC OCCLUSION SYNDROME ASSOCIATED TO GRAVES DISEASE

Background :Leriche syndrome or aortoiliac occlusion disease is caused by atherosclerosis and manifests as a constellation of symptoms that include claudication, erectile dysfunction, and the notable absence of femoral pulses. Graves disease (also known as Basedow) is an autoimmune disorder characterized by excessive thyroid hormone production, leading to hyperthyroidism. It often results in symptoms such as weight loss, rapid heart rate, tremors, and an enlarged thyroid gland (goiter).We present a case study detailing a singular occurrence of Leriche syndrome in a patient concurrently diagnosed with Graves disease, emphasizing the intricate nuances encountered in anesthesia management across both surgical procedures. Case presentation: A 53-year-old North African male with history of smoking presented to the ED with critical limb ischemia. The patient exhibited normal vital signs, except for a sinus tachycardia of 140 beats per minute. Initial blood laboratory tests yielded no abnormalities. However, abdominopelvic computed tomography angiography (CTA) revealed an abdominal aortic aneurysm measuring 46mm in diameter and extending over 107mm. This aneurysm was found to be partially thrombosed above the renal arteries, with complete thrombosis noted at the infrarenal level, extending bilaterally to the iliac arteries. The presence of collateral blood vessels supported the diagnosis of Leriche syndrome. Additionally, further investigation into the sinus tachycardia revealed the patients diagnosis of Graves disease, complicating the vascular surgery. After collegial discussion, a two-stage surgical approach was decided upon. Initially, the patient underwent medical treatment using a rapid thyroid hormone blocking protocol to manage the signs of hyperthyroidism. Following achievement of biochemical and clinical euthyroidism, characterized by stable thyroid hormone levels, the first surgery, total thyroidectomy, was performed. Subsequently, a few days later, the patient underwent a bypass surgery. The postoperative course was marked by successful bypass graft surgery, resulting in improved limb function and absence of further complications. The patient was discharged home 10 days after the second surgery. Conclusion : In this case, the challenge lay in managing both conditions while ensuring controlled heart rate and blood pressure to prevent aneurysm rupture, and concurrently administering anticoagulant therapy to prevent thrombus extension. Our findings suggest that in comparable cases, emphasis on thorough physical examination and medical history is crucial, and interdisciplinary collaboration between different specialties enhances patient survival.

Сценарная метонимия глаголов движения в русском языке

The aim of the study is to identify, based on motion verbs, the linguocognitive mechanism of scenario metonymy, the conditions of its realization in discourse, the potential of this metonymic model in representing human activities, and the trends of its development. The scientific novelty of the work lies in establishing, justifying, and describing the systematic nature of the scenario metonymy distinguished for the first time using motion verbs, which most consistently develops this type of secondary meaning. By conducting an analysis of typical utterances, the study is the first to determine the mechanism of forming metonymically derived meanings from verbs with the initial semantics of motion. This mechanism involves the following: in speech, these verbs become a way to denote complex, multi-act scenario-based events, whether they are everyday, singular occurrences, or significant periods of human activities. The metonymic representation of the most common multi-act events in speech is demonstrated. Additionally, the main constructions embodying the semantics of scenario metonymy, the characteristics of their lexical content, the systematic expansion of construction composition and the collocability of motion verbs within these constructions are identified for the first time.

Cold dark matter and holographic dark energy in f(R,T) theory of gravity

In this study, we have examined the cosmological model of the locally rotationally symmetric (LRS) Bianchi Type-I universe within the framework of the [Formula: see text] theory of gravity. The [Formula: see text] theory incorporates the Ricci scalar (R) and the trace of the energy–momentum tensor (T) in its formulation. Our investigation focuses on the cold dark matter (CDM) and holographic dark energy (DE) cosmological models, particularly in relation to the occurrence of a big rip singularity. To solve the field equation, we have assumed a specific relationship between the parameters, [Formula: see text] and [Formula: see text], where [Formula: see text] is proportional to [Formula: see text] and m is held constant. We have examined the existence of both the Big Bang and Big Rip singularities within this cosmological model. Additionally, we have analysed the state-finder parameter, which provides insights into the dynamics and evolution of the universe. Furthermore, we have discussed the physical and geometrical parameters of the universe in this context. These parameters help characterize and describe the behavior of the universe, shedding light on its underlying properties and dynamics. Through our investigation, we aim to deepen our understanding of the LRS Bianchi Type-I cosmological model within the [Formula: see text] theory of gravity, exploring the interplay between CDM, holographic DE, singularities, and the various parameters that contribute to the understanding of the universe.

Clinical differences between transient epileptic amnesia (TEA) and recurrent transient global amnesia (r-TGA)

Both transient epileptic amnesia (TEA) and transient global amnesia (TGA) are clinically characterized by temporary amnesic symptoms. TEA involves recurring amnesic episodes, while TGA typically manifests as a singular occurrence. TGA rarely occurs repeatedly, known as recurrent TGA (r-TGA), which complicates differentiation, and raises the possibility of overlap between two disorders. Given the effectiveness of suitable antiseizure medications (ASMs) in treating TEA, accurate diagnosis of the initial event is crucial. In this study, We retrospectively analyzed cases of sudden-onset amnesia at Juntendo University Hospital over the past 14 years. Our investigation identified a total of 17 patients with TEA who met the criteria established by Zeman, along with a total of 9 patients with r-TGA meeting Hodges’ criteria.Compared to r-TGA, TEA exhibited a higher recurrent rate, shorter symptoms, more additional symptoms, and increased structural abnormalities on head magnetic resonance imaging (MRI), and more abnormalities electroencephalography (EEG).Moreover, individual amnestic episode duration varied in both TEA and r-TGA. Our study reveals that TGA retains key features in recurrent cases and demonstrates distinctions from TEA. Nevertheless, distinguishing between the two conditions based solely on initial episodes remains challenging.

Evolution of coherence singularities in polarization singular beams.

The evolution of correlation singularities in partially coherent polarization singular beams (PC-PSBs) is investigated. Since PSBs are the superposition of two orthogonally polarized vortex beams, the occurrence of coherence singularities in PC-PSBs is strongly governed by the topological charge of the component vortex beams and the spatial coherence length. Coherence singularities appear in the form of ring dislocations in the modulus of the spectral degree of coherence (SDoC) profile, and the number of ring dislocations is equal to the higher value of the topological charge of the superposing vortex beam. Furthermore, the SDoC phase profile can be used to determine the polarity of a PC-PSB. The findings of the study could be valuable in various applications that rely on the spatial coherence of beams, such as free-space communication and imaging.

The Nameless Son of Wyryzmæg

In the Nart sagas, the story “The Nameless Son of Wyryzmæg” holds a unique position. In this tale, Barastyr, the lord of the dead, allows Wyryzmæg’s son to briefly leave his realm to persuade his father to make a yearly funerary offering in his name, following Ossetian tradition. The father, who unintentionally caused his son’s death, has completely repressed the tragic event to overcome grief and continue living as if it never happened. The opportunity to leave the Land of the Dead is a singular occurrence in the entire Nart cycle and stands in stark contrast to the story “Soslan in the Land of the Dead,” in which an Ossetian hero enters the afterlife while still alive and manages to return among the living.”

Exploring the Substantive Significance of Laryngoscopic Observations as Reliable Prognostic Indicators for the Therapeutic Efficacy in Cases of Laryngopharyngeal Reflux.

Laryngopharyngeal reflux (LPR) can be defined as the regurgitation of gastric acid and peptic substances into the laryngeal and hypopharyngeal regions, even in the case of a singular occurrence. A substantial body of recent research underscores the significance of non-acid reflux as a notable contributor to LPR symptoms. This current investigation delves into the assessment of laryngoscopic observations in their predictive capacity regarding the therapeutic outcomes of empirically administered proton pump inhibitor (PPI) therapy in the context of LPR. In this study, 145 patients who had received a clinical diagnosis of laryngopharyngeal reflux (LPR) underwent rigorous laryngoscopic examinations. These patients were subsequently categorized into three distinct groups based on the Belafsky reflux findings score, which included the criteria for normal (scores ranging from 0 to 7), mild to moderate (scores ranging from 8 to 16), and moderate to severe (scores ranging from 17 to 26). Among the participants, 12 individuals from the normal group, 44 from the mild to moderate group, and 31 from the moderate to severe group reported experiencing a noteworthy alleviation of symptoms following a three-month period of proton pump inhibitor (PPI) therapy and lifestyle adjustments. It is important to note that these findings yielded statistically significant results. Preliminary laryngoscopic observations hold significant potential as predictors of favourable treatment outcomes in the context of empirical proton pump inhibitor (PPI) therapy for laryngopharyngeal reflux (LPR).

Neoproterozoic potassic andesitic and lamprophyric rocks in the tupanci area, southernomost Brazil: Petrology and associated mineralization

Au and sulfide mineralizations occur in the Sul-Rio-Grandense Shield, and important occurrences of these metals are reported and attributed to the Lavras do Sul Shoshonitic Association (LSSA). Several authors point to a significant participation of andesitic and lamprophyric rocks in the formation of these deposits. The Tupanci area has the presence of andesites and lamprophyres, stratigraphically correlated to LSSA volcanic rocks (Hilário Formation), representing the northernmost exposures of this magmatism. The LSSA is one of the most complete Neoproterozoic Shoshonitic associations (ca. 592-590 Ma) in southern Brazil, containing plutonic, volcanic and hypabyssal rocks, related to the post-collisional stage of the Brasiliano/Pan-African orogeny. The andesitic rocks of the Tupanci area occur in the form of the lava flows, overlayed by volcanoclastic deposits, product of the reworking of the volcanic unit. Lamprophyres occur in the form of dykes, with N-NW direction, which are intruded in rocks of the metamorphic basement and in andesitic lava flows, being texturally separated and classified as spessartite and lamprophyric lapilli-tuff. The singular occurrence of the lamprophyric lapilli-tuff stands out, is analogous to Kimberley-type pyroclastic kimberlitic intrusions, depicting explosive manifestations linked to LSSA lamprophyres. The andesites and lamprophyres that ocour in Tupanci area show characteristics of high-K calc-alkaline or shoshonitic rocks, evidenced by LILE and LREE enrichment, negative Ti and Nb anomalies, plus positive Pb anomalies and the absence of Eu anomalies. These attributes reinforce the relationship of andesitic and lamprophyric rocks with related LSSA rocks. The presence of Au and Pt grains in the matrix of lamprophyric lapilli-tuff, highlights the economic importance of these rocks for the mineral occurrences in the region, where future studies can better define the metallogenetic potential for the rocks of the Tupanci area.

Particle swarm optimizer for the surface plasmon resonance effect on metal gratings.

In this work, the spectral dependence of optimum parameters of the surface plasmon resonance (SPR) effect on metallized sinusoidal diffraction gratings, under normal incidence, was determined using the particle swarm optimization method. The method was chosen due to its simplicity and effectiveness in providing reliable results, relative to direct search or gradient methods. The Rayleigh's hypothesis, which restricts the analysis to the case of shallow gratings, is used to model the diffracted fields across the interface between the sensing medium and metal. A penalty function was applied to avoid the occurrence of singularities and violation of the validity of the Rayleigh hypothesis. Using this procedure, the optimum values of grating periodicity and amplitude that maximized the sensitivity function for gold, silver, copper, and aluminum-metals that yield high quality factor SPR effects-were determined in a wavelength range between 500 and 1600 nm, for both gaseous and aqueous sensing media.

Quantum phase transition in NbN superconducting thin films

We systematically investigated the low-temperature transport properties of a series of NbN epitaxial films with thickness $t$ ranging from $\sim$2.0 to $\sim$4.0 nm. The films undergo a superconductor-insulator transition (SIT) with decreasing film thickness, and the critical sheet resistance for the SIT is close to the quantum resistance of Cooper pairs $h/4e^2$ (6.45 k$\Omega$). Besides the Berezinski-Koterlitz-Thouless transition, a magnetic-field-driven SIT is observed in those two-dimensional (2D) superconducting films (2.6 nm $\lesssim t \lesssim 4.0$ nm). Interestingly, it is found that the low-temperature magnetoresistance isotherms do not cross at a single fixed point but at a well-distinguished region for these superconducting films. The dynamical critical exponent obtained by analyzing these magnetoresistance isotherms is divergent as the quantum critical point is being approached. The behavior of the dynamical critical exponent, originating from quenched disorder at ultralow temperatures, provides direct evidence for the occurrence of quantum Griffiths singularity in the quantum phase transition process of the films. The field-driven anomalous metal (quantum metal) state does not appear in these films. Our results suggest that the quantum Griffiths singularity not only occurs in the highly crystalline 2D superconductors with superconductor-metal transition but also in those with SIT.

Heel-strike and toe-off walking of humanoid robot using quadratic programming considering the foot contact states

Heel-strike and toe-off (heel-toe) walking has been studied to increase step length, reduce the torque of the leg joints, or make robots walk similarly to humans. To realize heel-toe walking, it is necessary to determine the foot angle and ensure contact between the ground and the heel and toe. The foot angle for heel-toe walking can be analytically calculated considering the position of the center of mass (CoM) before the foot lands or rises. Therefore, the trajectory of the CoM of one cycle of walking must be known in advance. However, this method cannot be easily incorporated with model predictive control (MPC) to generate the trajectory of CoM in real time. This paper proposes a heel-toe walking method that can be used with the CoM trajectory generated using the MPC scheme. The CoM trajectory generation method that reduced the velocity fluctuation using MPC, which was proposed in a previous study, was used. The stability of the MPC scheme is proved in this paper. The quadratic programming is used to generate the heel-toe walking by considering the foot contact states as the constraints. The increase in step length and the decrease in singularity occurrence due to heel-toe walking were compared and analyzed in the simulation. The experiment verified the proposed heel-toe method.

Sharp Interface Methods for Simulation and Analysis of Free Surface Flows with Singularities: Breakup and Coalescence

A common feature of many free surface flows—drop/bubble breakup or coalescence and film/sheet rupture—is the occurrence of hydrodynamic singularities. Accurately computing such flows with continuum mechanical, multidimensional free surface flow algorithms is a challenging task given these problems’ multiscale nature, which necessitates capturing dynamics occurring over disparate length scales across 5–6 orders of magnitude. In drop breakup, the thinning of fluid threads that form and eventually pinch-off must be simulated until the thread's radius is about 10 nm. When two drops approach one another, the thickness of the fluid film separating them must fall below 10 nm before coalescence is said to have occurred. If the initial drop radii are 1 mm, simulations must remain faithful to the physics as thread radius or film thickness falls from 10−3 m to below 10−8 m. Here we review significant findings in interfacial flows with hydrodynamic singularities spearheaded by sharp interface algorithms. These multidimensional algorithms can achieve resolution that to date has only been possible with the use of simple 1D evolution equations.

The evolution of area-preserving and length-preserving inverse curvature flows for immersed locally convex closed plane curves

In this paper, we study an area-preserving inverse curvature flow and a length-preserving inverse curvature flow for immersed locally convex closed plane curves with rotation number m∈N+. The global-in-time flows are shown to converge smoothly to m-fold round circles as time goes to infinity. The sufficient conditions on initial curve are also found to guarantee the occurrence of the flow's singularity at finite time.

Generic naked singularities in Vaidya spacetimes

We investigate the occurrence of naked singularities, local and global, in the incoming Vaidya spacetimes with zero initial mass. While it is well-known that these spacetimes admit locally and globally naked singularities, we demonstrate that globally naked singularities are significantly more common than is stressed in the literature, being generic in a natural topology on this collection of spacetimes. A heuristic consequence of the results is that the slow accumulation of mass is both necessary and sufficient for both types of naked singularity in these spacetimes. We demonstrate that the naked singularity, as long as it exists, always has divergent curvature (Kretschmann scalar) associated to it along emerging null curves, regardless of the form of the mass function. In particular, a consequence is that the curvature strength of the singularity cannot be smoothed away.

Bounce Universe with Finite-Time Singularity

This work explains how the presence of a Type-IV singularity (a mild singularity) can influence the dynamics of a bouncing universe. In particular, we examine the bounce cosmology that appears with a Type-IV singularity in the context of a ghost-free Gauss–Bonnet theory of gravity. Depending on the time of occurrence of the Type-IV singularity, three different cases may arise—when the singularity occurs before the bounce, after the bounce, or at the instant of the bounce. However, in all of these cases, we find that in the case when the singularity “globally” affects the spacetime, the scalar power spectrum becomes red-tilted, and the tensor-to-scalar ratio is too large to be consistent with the observational data. Based on these findings, we investigate a different bouncing scenario which also appears with a Type-IV singularity, and wherein the singularity affects the spacetime “locally” around the time when it occurs. As a result, and unlike the previous scenario, the perturbation modes in the second bouncing scenario are likely to be generated far away from the bounce in the deep contracting phase. This finally results in the simultaneous compatibility of the observable quantities with the Planck data and ensures the viability of the bounce model where the Type-IV singularity has local effects on the spacetime around the time of the singularity.

Modified theories of gravity: Why, how and what?

General Relativity (GR) was proven via the direct detection of gravitational waves from the mergers of the binary black holes and binary neutron stars by the Advanced LIGO and Advanced Virgo detectors. These detections confirmed the prediction of GR and provided the first direct evidence of the existence of stellar-mass black holes (BHs). However, the occurrence of singularities at the centers of BHs suggests that GR is inapplicable because of the breakdown of the equivalence principle at the singularities. The fact that these singularities exist indicates that GR cannot be a universal theory of space-time. In the low-energy limit, the theoretical and observational challenges faced by the $\Lambda$CDM model also indicate that we might have to look beyond GR as the underlying theory of gravity. Unlike GR, whose field equations contain only up to second-order derivatives, the modified theories with higher derivative Ricci/Riemann tensor gravity models include higher derivatives. Therefore, one expects significant differences between GR and modified theories. Since there are many ways of modifying GR in the strong-gravity and cosmological distances, each model has unique features. This leads to the following crucial question: Are there a set of unique signatures that distinguish GR from modified gravity (MG) theories? This review discusses three aspects of MG theories: (1) Why do we need to consider MG theories? (2) How to modify GR? and (3) What are the observational consequences? The review is written in a pedagogical style with the expectation that it will serve as a useful reference for theorists and observers and those interested in bridging the divide between theory and observations.

The Motion Formalism for Flexible Multibody Systems

Abstract This paper describes a finite element approach to the analysis of flexible multibody systems. It is based on the motion formalism that (1) uses configuration and motion to describe the kinematics of flexible multibody systems, (2) recognizes that these are members of the special Euclidean group thereby coupling their displacement and rotation components, and (3) resolves all tensors components in local frames. The goal of this review paper is not to provide an in-depth derivation of all the elements found in typical multibody codes but rather to demonstrate how the motion formalism (1) provides a theoretical framework that unifies the formulation of all structural elements, (2) leads to governing equations of motion that are objective, intrinsic, and present a reduced order of nonlinearity, (3) improves the efficiency of the solution process, and (4) prevents the occurrence of singularities.

THE AFFIRMATION OF DEATH

Finitude as an affirmative moment is what stands at the center of this paper. While death cannot be represented or conceptualized, it is present in events of death in the life of an individual and of a society. Here we look at formations split between the presencing of death and death’s denial or deferral as ways of symbolizing death as imminently present and certain for those who live. Death is affirmed as what cannot be known, represented, or imagined. Based on the Freudian death drive and its interpretation, I look into poetic and philosophical instances of this idea of affirmation: from Freud’s dreams of dead people who return to the scene of the living, through inventive modes of recounting death in its singular occurrence, to modes of presencing death in war, mourning, melancholia, and tragedy as well as in philosophical ideas regarding the necessary, irreducible presence of death in language or culture. All these work as symbolic formations that enact the presence of death in the form of denial. The disruptive presence of death in the life of a culture and of singular life, the presence of what is necessary yet cannot be known or represented, attests to the irreducible inclination of the human psyche toward its ownmost death.