Background Solution Research Articles

Mimicking Wormholes in Born–Infeld Electrodynamics

We compute the evolution of linear perturbations on top of a background solution of a general nonlinear electromagnetic theory. This evolution can be described in terms of two effective metrics, and we analyze under what conditions they are conformally related so that they can be regarded as analog models of non-trivial gravitational fields in the eikonal approximation. This is the case in Born–Infeld theory. For the background created by a static point electric charge in the Born–Infeld theory, the effective metric describes a wormhole geometry for light rays. Depending on the impact parameter, incoming light rays are either scattered to infinity or approach the wormhole slowing down their pace until they hit the charge at vanishing speed. The same effective wormhole geometry is obtained for a magnetic monopole and a dyon and we relate it to the duality invariance of Born–Infeld electromagnetism. Finally, we analyze the scalar Dirac–Born–Infeld theory and show that the effective wormhole geometry is not generated by a particle with scalar charge.

Gauge theory meets cosmology

We reconsider linear perturbations around general Friedmann-Lemaitre-Robertson-Walker (FLRW) cosmological backgrounds. Exploiting gauge freedom involving only time reparametrizations, we write down classical background solutions analytically, for an arbitrary number of fluid components. We then show that the time evolution of scalar and tensor adiabatic perturbations are governed by Schrödinger-like differential equations of generalized Heun type. After recovering known analytic results for a single-component fluid, we discuss more general situations with two and three different fluid components, with special attention to the combination of radiation, matter and vacuum energy, which is supposed to describe the ΛCDM model. The evolution of linear perturbations of a flat ΛCDM universe is described by a two-transient model, where the transitions from radiation to matter and matter to vacuum energy are governed by a Heun equation and a Hypergeometric equation, respectively. We discuss an analytic approach to the study of the general case, involving generalized Heun equations, that makes use of (quantum) Seiberg-Witten curves for 𝒩 = 2 supersymmetric gauge theories and has proven to be very effective in the analysis of Black-Hole, fuzzball and ECO perturbations.

Tracking autonomic nervous system activity using surface ECG: Personalized, multiparametric evaluation

We present a concise review of the background, pitfalls, and potential solutions for the noninvasive evaluation and continuous tracking of cardiac autonomic nervous system activity (ANSA), using surface-ECG-accessible parameters, including heart rate (HR), heart-rate variability (HRV), and cardiac repolarization. These parameters have provided insights into the dynamics of cardiac ANSA in controlled experiments and have proved useful in risk assessment with respect to sudden cardiac death and all-cause mortality in some patient populations, as well as in implantable device programming. Yet attempts to translate these parameters from the laboratory environment to ambulatory settings have been hampered by the presence of multiple uncontrolled factors, including changes in blood pressure, body position, physical activity, and respiration frequency. We show that a single-parameter-based, simplified cardiac ANSA evaluation in an uncontrolled ambulatory setting could be inaccurate, and we discuss several approaches to improve accuracy. Discerning cardiac ANSA effects in uncontrolled ambulatory environments requires tracking multiple physiological processes, preferably using multisensor, multiparametric monitoring and controlling some physiological variables (e.g., respiration frequency); data fusion and machine-learning-based analytics are instrumental for developing more accurate personalized ANSA evaluation.

Estimation of the adaptogenic potential of melatonin on salinity resistance of spring wheat seeds and sprouts

The current paper is devoted to the study of melatonin as an adaptogen capable of increasing wheat tolerance to stress caused by excess levels of easily soluble salts in the environment. The purpose of the study was to evaluate, within the framework of a laboratory model experiment, the ability of melatonin to increase seed germination and stimulate growth processes in wheat sprouts against the background of salinity. The study was conduc ted at the FSBI All-Russian Scientific Research Institute of Agrochemistry named after D.N. Pryanishnikov in 2024. The study objects were seeds of the spring wheat variety ‘Darya’. Before the experiment, the seeds were treated with aqueous solutions of melatonin in concentrations of 0; 0.01; 0.1; 1 and 10 mg/l using the priming method. Distilled water and a 150 mM sodium chloride solution were used as background solutions for germination. As a result, there has been shown that within the framework of the experiment, there is an increase in seed germination against the background of treatment with melatonin solutions in concentrations from 0.1 to 10 mg/l against a saline background. Seed treatment with melatonin has demonstrated a pronounced growth-stimulating effect on wheat sprouts, especially in relation to the root system. However, the strength of this effect was somewhat reduced on a saline background compared to control conditions. There was a maximum growth-stimulating effect of melatonin on both backgrounds when using a solution with a concentration of 1 mg/l. There was also established that priming seeds with melatonin promoted water retention in seedling root cells, which may be one of the mechanisms for increasing plant resistance to salinity.

Meso-inflationary Peccei–Quinn Symmetry Breaking with Nonminimal Coupling

We study a realization of the inflationary scenario where the Peccei–Quinn (PQ) symmetry is spontaneously broken during inflation, facilitated by its nonminimal coupling to gravity. This results in, effectively, a two-field inflation: the early stage is driven by an inflaton field with the PQ symmetry intact, and the later stage is driven by the PQ scalar after its effective mass becomes tachyonic, causing destabilization from the origin. The nonminimal coupling serves the dual purpose of restoring the PQ symmetry during early inflation and flattening the PQ potential posttachyonic shift, allowing for continued slow-roll. We analyze the inflationary background solutions and scalar perturbations, which are amplified at small scales via significant isocurvature perturbations generated near the symmetry-breaking epoch. These perturbations lead to second-order gravitational waves, detectable by next-generation space-based experiments.

On the lifespan of nonzero background solutions to a class of focusing nonlinear Schrödinger equations

The global solvability in time and the potential for blow-up of solutions to non-integrable focusing nonlinear Schrödinger equations with nonzero boundary conditions at infinity present challenges that are less explored and understood compared to the case of zero boundary conditions. In this work, we address these questions by establishing estimates on the lifespan of solutions to non-integrable equations involving a general class of nonlinearities. These estimates depend on the size of the initial data, the growth of the nonlinearity, and relevant quantities associated with the amplitude of the background. The estimates provide quantified upper bounds for the minimum guaranteed lifespan of solutions. Qualitatively, for small initial data and background, these upper bounds suggest long survival times consistent with global existence of solutions. On the other hand, for larger initial data and background, the estimates indicate the potential for the intriguing phenomenon of instantaneous collapse in finite time. These qualitative theoretical results are illustrated via numerical simulations. Furthermore, importantly, the numerical findings motivate the proof of improved theoretical upper bounds that provide excellent quantitative agreement with the order of the numerically identified lifespan of solutions.

On the stability of electrovacuum space-times in scalar–tensor gravity

We study the behavior of static, spherically symmetric solutions to the field equations of scalar–tensor theories (STT) of gravity belonging to the Bergmann–Wagoner–Nordtvedt class, in the presence of an electric and/or magnetic charge. This class of theories includes the Brans–Dicke, Barker and Schwinger STT as well as nonminimally coupled scalar fields with an arbitrary parameter ξ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\xi $$\\end{document}. The study is restricted to canonical (nonphantom) versions of the theories and scalar fields without a self-interaction potential. Only radial (monopole) perturbations are considered as the most likely ones to cause an instability. The static background solutions contain naked singularities, but we formulate the boundary conditions in such a way that would preserve their meaning if a singularity is smoothed, for example, due to quantum gravity effects. These boundary conditions look more physical than those used by other authors. Since the solutions of all STT under study are related by conformal transformations, the stability problem for all of them reduces to the same wave equation, but the boundary conditions for perturbations (and sometimes the boundaries themselves) are different in different STT, which affects the stability results. The stability or instability conclusions are obtained for different branches of solutions in the theories under consideration and are presented in a table form.

Rogue waves and nonzero background solutions for the Gross–Pitaevskii equation with a parabolic potential

In this paper an integrable Gross–Pitaevskii equation with a parabolic potential and a gain term is investigated. Its solutions with a nonzero background are derived. These solutions are constructed by using biliearization reduction approach and connections between the nonlinear Schrödinger equation and the Gross–Pitaevskii equation. The solutions are presented in double-Wronskian form and are classified in terms of canonical forms of a certain matrix. Various breathers and rogue waves are analyzed and illustrated.

Biosurfactant-mediated transport of tetracycline antibiotics in saturated porous media: Combined effects of the chemical properties of contaminants and solution chemistry conditions

The mobility of tetracycline antibiotics (TCs) in saturated aquifers is possibly affected by the presence of biosurfactants, which are widespread in the aquatic/soil environments. This study investigated the mobility characteristics of various tetracyclines—specifically tetracycline (TC), oxytetracycline (OTC), and chlortetracycline (CTC)—within quartz sand columns in the presence of rhamnolipid, a common biosurfactant. Exogenous rhamnolipid significantly inhibited the transport of the three TCs over the pH range of 5.0–9.0 (e.g., the mass of retained TC, OTC, and CTC increased from 32.6 %, 26.9 %, and 39.2 % (in the absence rhamnolipid) to 39.4 %, 38.9 %, and 51.7 % (in the presence of rhamnolipid), respectively). This observation could be attributed to the bridging effects of this biosurfactant. Specifically, the hydrophilic head of rhamnolipid molecules is likely associated with the surfaces of sand grains through surface complexation and/or hydrogen bonding interactions. Accordingly, the hydrophobic moieties of the deposited rhamnolipid molecules (i.e., the aliphatic chains) interact with the hydrophobic groups of TCs molecules via hydrophobic interactions. Interestingly, the extent of the inhibitory effect on CTC mobility was greater than that on OTC and TC, which was related to the different hydrophobic characteristics of the three antibiotics. Furthermore, the inhibitory effect of rhamnolipid on the transport of TCs diminished as the pH of the background solution increased. This observation was attributed to the weakened bridging effects, resulting from the reduced deposition of the biosurfactant on the sand surfaces. Additionally, the cation-bridging mechanism involved in the retention of TCs in the addition of rhamnolipid when the background electrolyte was Ca2+ (i.e., Ca2+ ions served as bridging agents between the deposited rhamnolipid molecules and TCs). The insightful findings enhance our understanding of the critical roles of biosurfactants in influencing the environmental dynamics and ultimate fate of conventional antibiotic pollutants within groundwater systems.

Assessing Adsorption Behavior of Molybdenum in Soils: An Emerging Metal Contaminant

Molybdenum (Mo) is an essential micronutrient for most living organisms but also an emerging contaminant in the environment. A narrow range exists between critical requirements for plants (0.5 mg kg-1) and threshold toxicity of molybdenum (10 mg kg-1) to ruminants, considered as “molybdenosis”. Adsorption is one of the most important chemical processes in soils that affect the mobility of metals/contaminants in soil. To evaluate the sorption behaviour of molybdenum in soils, twenty bulk surface soil samples (0–15 cm) with diverse physical and chemical properties were collected from different parts of India. A laboratory experiment was conducted to study the sorption behaviour of Mo in soil under two temperature (20 and 30○ C) conditions. Five graded Mo concentrations (1, 2, 5, 10, 20, and 50 mg L-1) were prepared using (NH4 ) 6 Mo7 O24 in a 0.005 M Ca(NO3 ) 2 background solution. Maximum adsorption of Mo was observed in the soils where pH ranges from 4-5, while in alkaline soils (pH > 8) negative adsorption phenomena were found. Freundlich isotherm fitted better than Langmuir isotherm in a wide range of soil’s pH. A highly significant negative correlation was observed between soil pH and adsorption parameters, while a significant positive correlation was found between SOC and adsorption parameters. The thermodynamic parameters i.e., free energy (∆G○ ), enthalpy (∆H○ ), and entropy (∆S○ ) were determined using sorption data in two different temperature conditions. It was observed that molybdenum sorption in soil is a spontaneous endothermic reaction. This study highlighted the role sorption mechanism in the evaluation of mobility and availability of molybdenum in different soil chemical environments.

Scalar perturbations from inflation in the presence of gauge fields

We study how Abelian-gauge-field production during inflation affects scalar perturbations in the case when the gauge field interacts with the inflaton directly (by means of generic kinetic and axial couplings) and via gravity. The homogeneous background solution is defined by self-consistently taking into account the backreaction of the gauge field on the evolution of the inflaton and the scale factor. For the perturbations on top of this background, all possible scalar contributions coming from the inflaton, the metric, and the gauge field are considered. We derive a second-order differential equation for the curvature perturbation, ζ, capturing the impact of the gauge field, both on the background dynamics and on the evolution of scalar perturbations. The latter is described by a source term in the ζ equation, which is quadratic in the gauge-field operators and leads to non-Gaussianities in the curvature perturbations. We derive general expressions for the induced scalar power spectrum and bispectrum. Finally, we apply our formalism to the well-known case of axion inflation without backreaction. Numerical results show that, in this example, the effect of including metric perturbations is small for values of the gauge-field production parameter ξ>3. This is in agreement with the previous results in the literature. However, in the region of smaller values, ξ≲2, our new results exhibit order-of-unity deviations when compared to previous results. Published by the American Physical Society 2024

Axialgravisolitons at infinite corner

Abstract Gravitational solitons (gravisolitons) are particular exact solutions of Einstein field equation in vacuum build on a given background solution. Their interpretation is not yet fully clear but they contain many of the physically relevant solutions low N-solitons solutions. 
However, a systematic study and characterization of gravisolitons solution for every N is lacking and their relevance in a theory of quantum gravity is not fully understood. This work aims to investigate and characterize some properties of N-axialsoliton solutions such as their asymptotically behaviour and asymptotic symmetries given minimal assumptions on the background metric. We develop an explicit systematic asymptotically expansion for the N-axialsoliton solution and we compute the leading order of the asymptotic killing vectors. Moreover, in the perspective to better understand the role of gravisolitons in quantum gravity we make a link, and a one of the first explicit test, to the corner symmetry proposal deriving which subalgebra of the universal corner symmetry algebra is generated by the asymptotic Killing vectors of N-axialsoliton solution. In the spirit of the corner proposal, the axialgravisoliton corner symmetry algebra (agcsa) can be useful for the quantization of the non-asymptotically flat sector of gravity while, in the spirit of IR triangle, new soft theorems and memory effects could emerge.

More on spin-2 operators in holographic quantum mechanics

We study the spectrum, unitarity bound and holographic central charge of spin-2 operators in a warped AdS2 × S2 × T4 × Iψ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {\\mathcal{I}}_{\\psi } $$\\end{document} × Iρ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {\\mathcal{I}}_{\\rho } $$\\end{document} background in the Type IIB theory. We were able to identify a class of solutions that is completely independent of the functions that define the background solution. We comment on the relation of our results to the previous ones in the literature.

Kinetic aspects of salinity stability of layer-by-layer polyelectrolyte nanofiltration membranes: Impact of soaking time, types of ions and crosslinking

Recent discovery of very high selectivity of Layer-by-Layer (LBL) nanofiltration (NF) membranes for mono/bivalent ions has attracted significant attention, especially for extraction of lithium from salt lake brines. Besides the exceptionally high selectivity, the salinity stability in highly saline solutions (HSS) that often occurred during NF has been largely neglected. Intuitively, because the LBL membranes are assembled in a saline background solution, the assembly disassembles in highly saline environments. To verify above argument, we reported here a comprehensive study on the performance of polystyrene sulfonate (PSS)/poly(diallyldimethylammonium chloride) (PDADMAC) and PSS/poly(allylamine) hydrochloride (PAH) LBL NF membranes in HSS by short/long term immersion and dynamic filtration. Greater binding strength of (PSS/PAH)2.5 corresponded to better salinity stability than (PSS/PDADMAC)2.5. Adsorption bridging of divalent Mg2+ with PSS altered PSS conformation and narrowing the pore size distribution. Compared to static immersion, dynamic filtration accelerated the loss of PEs from (PSS/PAH)2.5 at cLiCl = 2 mol/L, but membrane stability was improved by chemical crosslinking. This research highlighted the kinetic aspects in salinity stability and the chemical-physical behavior of polyelectrolyte complexes (PECs) in HSS. The results offer valuable insights for development of LBL NF membranes for ion separation and resource recovery.

Selection of structure-induced aptamer targeting small molecule based on capillary sieving electrophoresis.

In this study, a structure-induced aptamer targeting small molecules was selected using capillary sieving electrophoresis (CSE). CSE was conducted using a capillary filled with a background solution containing hydroxypropyl cellulose as a sieving matrix to separate the aptamer candidates by changing their structures via complexation. Before aptamer selection, the original random-sequence DNA library was used to create structure-not-preorganized DNA sub-library containing straight-chain-like structures using CSE. Next, a structure-induced aptamer targeting L-tyrosinamide was selected from the prepared sub-library. Six aptamer candidates were selected, one of which showed a binding ability comparable to that of the reported L-tyrosinamide aptamer and selectivity toward the analogs. These results indicated that the proposed method can be applied to select structure-induced aptamers that target small molecules.

#2784 Deep learning algorithm predicts individual ultrafiltration trajectories for patients on automated peritoneal dialysis 12 weeks ahead

Abstract Background and Aims Adequate small solute clearance and ultrafiltration (UF) are the main requirements for fluid and salt homeostasis on peritoneal dialysis (PD). New automated peritoneal dialysis (APD) systems that allow remote patient monitoring in terms of PD treatment analysis have the potential to improve clinical outcomes. UF on APD although dependent on PD prescription, i.e. fill volumes and glucose concentration, exhibits substantial intra- and interindividual variation, even day-by-day. As conventional statistical methods are not able to assess these complex non-linear relationships adequately, we aimed to build a deep learning algorithm to predict ultrafiltration trajectories of individual patients 12 weeks ahead. Method Data on daily UF and PD prescriptions (i.e., glucose concentration, fill volumes) was extracted from the APD cycler management software (PD Link, Baxter, IL, USA) and patient charts at the Medical University of Vienna, for a secondary analysis of this cohort. The Keras high-level API for TensorFlow in R software (R Core Team 2023) was used to create a Long Short-Term Memory (LSTM) recurrent neural network based on historic prescription and gcUF data of 26 weeks (after the first 90 days of APD) to predict individual UF trajectories for the following 12 weeks. Results APD machine readouts from a total of 123 patients, with a mean time on PD of 117 (±73) days, were retrieved. The final recurrent neural network consisted of four LSTM layers with 64 cells each, sigmoid activation. The final model was fit using 30 epochs, 49 steps per epoch, and recurrent dropout to avoid overfitting. A 40-40-20% data split was used to train, validate, and test the model adequately. This deep learning algorithm was able to predict individual UF values, for each day of the upcoming 12 weeks, with an accuracy of at mean 201ml. Upon visual inspection, predicted individual UF trajectories smoothly resemble the overall day-by-day trajectory of the patient but fail to account for extreme spikes in either direction. Conclusion In conclusion, historic daily APD cycler and prescription data in coalescence with respective daily measurements of membrane function (i.e., gcUF) can be used to predict individual daily ultrafiltration values and trajectories of APD patients 12 weeks ahead using a deep learning algorithm. Therefore, continuous collection of PD prescription data and UF measurements may be used to monitor peritoneal membrane function of patients on APD and alert clinical teams upon detection of relevant changes of UF trajectories already 12 weeks ahead to facilitate early intervention. In contrast to current “screening” methods on PD, i.e., Peritoneal Equilibrium Test, these methods could reduce treatment burden.

A worldsheet description of flux compactifications

We demonstrate how recent developments in string field theory provide a framework to systematically study type II flux compactifications with non-trivial Ramond-Ramond profiles. We present an explicit example where physical observables can be computed order by order in a small parameter which can be effectively viewed as string coupling constant. We obtain the corresponding background solution of the string field equations of motions up to the second order in the expansion. Along the way, we show how the tadpole cancellations of the string field equations lead to the minimization of the F-term potential of the low energy supergravity description. String field action expanded around the obtained background solution furnishes a “worldsheet” description of the flux compactifications.

Unifying inflationary and reheating solution

The conventional background solution for the evolution of a single canonical inflaton field performs admirably in extreme scenarios such as the slow-roll phase (where the slow-roll parameter is much less than one) and the deep reheating era (where the Hubble parameter is much smaller than the effective mass of the potential and the field oscillates around the minimum of the potential), but fails to accurately depict the dynamics of the Universe around the end of inflation and the initial oscillatory phases. This article proposes a single, unified, model-independent, parametrized analytical solution for such models that bridges the gap between these two extremes, providing a near-accurate comprehensive description of the evolution of the Universe. This novel strategy has the potential to substantially enhance both quantitative and qualitative cosmological observational predictions, and, as a consequence, can further constrain the inflationary models more effectively using future observations.

On the Nonlinear Two- and Three-Dimensional Klein–Gordon Equations Allowing Localized Solutions with Beatings of Coupled Oscillators

Equations for two and three scalar fields, which allow localized solutions with beatings of coupled oscillators, have been presented. The amplitude of oscillations of a localized perturbation for one field decreases periodically gradually to a minimum and the amplitudes of the other scalar fields increase to a maximum; then, the reverse process occurs. In this case, all fields except for one are initially either in the state of a background solution with a small amplitude or equal to zero. Such solutions can be interesting due to analogy with neutrino oscillations. Equations of motion, where the perturbation of one of the components is obligatorily accompanied by the perturbation of the second and third components even in zeroth background state, have also been presented. It has been shown that these equations satisfy the energy conservation law.

The influence of water acidity and alkalinity on the adhesion properties of bitumen-aggregate interface

To examine the influence of water acidity and alkalinity on bitumen-aggregate interfacial adhesion, we measured interaction force between aggregate and bitumen using atomic force microscopy with a 1 mmol/L KCl background solution at pH levels ranging from 2 to 10. Experimental materials included four types of aggregates (basalt, granite, limestone A, and limestone B) and two types of bitumen (Zhenhai 90# matrix and Styrene-Butadiene-Styrene modified). Results showed adhesion rankings: granite < basalt < limestone B < limestone A. Long-range forces increased with higher pH, in line with Derjaguin-Landau-Verwey-Overbeek theory. Acidic conditions reduced repulsive forces between bitumen and aggregates while increasing adhesive forces. Compared with the Zhenhai 90# matrix bitumen, Styrene-Butadiene-Styrene modified bitumen demonstrated superior adhesion. Zeta potential values for bitumen and aggregate consistently decreased with rising pH, reflecting the aggregate-bitumen interaction force, suggesting electrostatic forces' dominance. Boiling water method was used to assess bitumen spalling on different aggregates under varied acid-base conditions, finding a significant correlation between spalling rate and microscopic interaction force. This study offers theoretical support for minimizing water damage in bitumen pavements by shedding light on the adhesion process of bitumen and aggregates in wet settings.