bluuebunny/crossref_metadata_2025 huggingface dataset:
A Novel Portable, Mobile MRI: Comparison with an Established Low-Field Intraoperative MRI System
Authors: Bossert Sharon , Unadkat Prashin , Sheth Kevin N. , Sze Gordon , Schulder Michael
Published: September 2023

Background MRI (magnetic resonance imaging) using low-magnet field strength has unique advantages for intraoperative use. We compared a novel, compact, portable MR imaging system to an established intraoperative 0.15 T system to assess potential utility in intracranial neurosurgery.

Methods Brain images were acquired with a 0.15 T intraoperative MRI (iMRI) system and a 0.064 T portable MR system. Five healthy volunteers were scanned. Individual sequences were rated on a 5-point (1 to 5) scale for six categories: contrast, resolution, coverage, noise, artifacts, and geometry.

Results Overall, the 0.064 T images (M = 3.4, SD = 0.1) had statistically higher ratings than the 0.15 T images (M = 2.4, SD = 0.2) (p < 0.01). All comparable sequences (T1, T2, T2 FLAIR and SSFP) were rated significantly higher on the 0.064 T and were rated 1.2 points (SD = 0.3) higher than 0.15 T scanner, with the T2 fluid-attenuated inversion recovery (FLAIR) sequences showing the largest increment on the 0.064 T with an average rating difference of 1.5 points (SD = 0.2). Scanning time for the 0.064 T system obtained images more quickly and encompassed a larger field of view than the 0.15 T system.

Conclusions A novel, portable 0.064 T self-shielding MRI system under ideal conditions provided images of comparable quality or better and faster acquisition times than those provided by the already well-established 0.15 T iMR system. These results suggest that the 0.064 T MRI has the potential to be adapted for intraoperative use for intracranial neurosurgery.
Review: Microbial Therapeutics for Liver Disease
Authors: Philips Cyriac Abby , Augustine Philip
Published: September 2023

The human gut contains many microorganisms, including bacteria, fungi, viruses, and archaea. Patients with liver disorders have altered intestinal flora and disrupted gut barriers. The role of the gut microbiota in the pathophysiology of many liver disorders is apparent from preclinical models and clinical studies. High-quality studies showed that people with acute or chronic liver disorders of various etiologies, such as non–alcohol- and alcohol-related liver disease, chronic hepatitis virus infection, chronic cholestatic liver disease, and liver cirrhosis and related complications, have less diverse gut flora and associated perturbed microbial functional metabolism. In this review, we discuss unique therapeutic strategies for various liver diseases that involve manipulating the gut microbiota using various methods. We provide a summary of the most recent information on untargeted methods for treating liver illnesses, such as probiotics, prebiotics, and postbiotics, fecal microbiota transplantation, and precision microbiome-centered treatments (e.g., engineered microbes). Recent research suggests that altering the gut microbiota in various ways might slow the onset of liver disease and lessen the associated clinical complications. Growing evidence suggests that antimicrobial therapy with rifaximin can beneficially alter the gut microbiome to reduce hepatic encephalopathy, portal hypertension, and systemic inflammation in decompensated cirrhosis. At the same time, a healthy donor stool transplant improves transplant-free survival in severe alcohol-associated hepatitis, prevents hepatic encephalopathy, and reduces incident and intercurrent infections and multidrug resistance in decompensated cirrhosis.
Minimally Invasive Surgery for Managing Grade IV and V Spondylolisthesis
Authors: Ramirez Velandia Felipe , Gomez Cristancho David Camilo , Urrego Nieto Andres , Marquez Isabel , Restrepo Martinez Alejandra , Becerra Ospina Jaime Eduardo , Pérez Rodriguez Juan Carlos
Published: September 2023

Surgical treatment of high-grade spondylolisthesis is controversial and aims at restoring the spinopelvic sagittal balance through complete or partial reduction of the listhesis. Nerve decompression and interbody fusion are necessary for patients presenting with neurological deficit, severe pain, lower limb asymmetry, or deformities. We present the case and the results of a patient with high-grade spondylolisthesis, in whom minimally invasive management was performed. A narrative review in this topic is also provided.

We performed a literature review of high-grade spondylolisthesis to compare our technique to current surgical alternatives. We included articles from PubMed, Embase, Scopus, Ovid, and Science Direct published between 1963 and 2022 that were written in English, German, and Spanish. The terms used were the following: “high grade spondylolisthesis,” “spondyloptosis,” “surgical management,” “interbody fusion,” and “arthrodesis.” In all, 485 articles were displayed, from which we filtered 112 by title and abstract. At the end, 75 references were selected for the review.

Different interbody fusion techniques can be used to correct the lumbosacral kyphosis and restore the spinopelvic parameters. A complete reduction of the listhesis is not always required. The surgical procedure carried out in our patient corresponds to the first known case of minimally invasive circumferential arthrodesis with iliac screws and sacral fixation in a high-grade dysplastic spondylolisthesis. This approach guarantees the correction of the lumbosacral kyphosis and a complete reduction of the listhesis. Further studies are required to determine whether the results of this case can be extrapolated to other patients with high-grade spondylolisthesis.
Pulse Pressure Variance (PPV)-Guided Fluid Management in Adult Patients Undergoing Supratentorial Tumor Surgeries: A Randomized Controlled Trial
Authors: Gopal Janani , Srivastava Shashi , Singh Nidhi , Haldar Rudrashish , Verma Ruchi , Gupta Devendra , Mishra Prabhakar
Published: September 2023

Objective Appropriate fluid management in neurosurgery is critical due to the risk of secondary brain injury. Determination of volume status is challenging with static variables being unreliable. Goal-directed fluid therapy with dynamic variables allows reliable determination of fluid responsiveness and promises better outcomes. We aimed to compare the intraoperative fluid requirement between conventional central venous pressure (CVP)-guided and pulse pressure variance (PPV)-guided fluid management in supratentorial tumor surgeries.

Materials and Methods This prospective, randomized, double-blind, single-center trial was conducted with 72 adults undergoing supratentorial tumor surgery in a supine position. Patients were divided into two groups of 36 patients each receiving CVP- and PPV-guided fluid therapy. The CVP-guided group received boluses to target CVP greater than 8 mm Hg along with hourly replacement of intraoperative losses and maintenance fluids. The PPV-guided group received boluses to target PPV less than 13% in addition to maintenance fluids. Total intraoperative fluids administered and the incidence of hypotension was recorded along with the brain relaxation score. Postoperatively, serum lactate levels, periorbital and conjunctival edema, as well as postoperative nausea and vomiting were assessed.

Statistical Analyses All statistical analyses were performed with Statistical Package for Social Sciences, version-20 (SPSS-20, IBM, Chicago, Illinois, United States). To compare the means between the two groups (CVP vs. PPV), independent samples t-test was used for normal distribution data and Mann–Whitney U test for nonnormal distribution data. The chi-square test or Fischer's exact test was used for categorical variables.

Results The CVP group received significantly more intraoperative fluids than the PPV group (4,340 ± 1,010 vs. 3,540 ± 740 mL, p < 0.01). Incidence of hypotension was lower in the PPV group (4 [11.1%] vs. 0 [0%], p = 0.04). Brain relaxation scores, serum lactate levels, periorbital and conjunctival edema, and incidence of postoperative nausea and vomiting were comparable between the groups.

Conclusion The requirement for intraoperative fluids was less in PPV-guided fluid management with better hemodynamic stability, adequate brain conditions, and no compromise of perfusion.
Emergence Patterns from General Anesthesia after Epilepsy Surgery: An Observational Pilot Study
Authors: Venkatraghavan Lashmi , Bhardwaj Suparna , Banik Sujoy , Chowdhury Tumul , McAndrews Mary Pat , Valiante Taufik
Published: September 2023

Objective Emergence from anesthesia starts from the limbic structures and then spreads outwards to brainstem, reticular activating systems, and then to the cortex. Epilepsy surgery often involves resection of limbic structures and hence may disrupt the pattern of emergence. The aim of this study was to explore the pattern of emergence from anesthesia following epilepsy surgery and to determine associated variables affecting the emergence pattern.

Setting and Design Tertiary care center, prospective observational study.

Materials and Methods We conducted a prospective observation pilot study on adult patients undergoing anterior temporal lobectomy and amygdalohippocampectomy for epilepsy. Anesthesia management was standardized in all patients, and they were allowed to wake up with “no touch” technique. Primary outcome of the study was the pattern of emergence (normal emergence, agitated emergence, or slow emergence) from anesthesia. Secondary outcomes were to explore the differences in preoperative neuropsychological profile and limbic structure volumes between the different patterns of emergence. Quantitative variables were analyzed using Student's t-test. Qualitative variables were analyzed using chi-square test.

Results Twenty-nine patients completed the study: 9 patients (31%) had agitated emergence, and 20 patients had normal emergence. Among the agitated emergence, 2 patients had Riker scale of 7 indicating violent emergence. Patient demographics, anesthetic used, neuropsychological profile, and limbic structure volumes were similar between normal emergence and agitated emergence groups. However, two patients who had severe agitation (Riker scale of 7) had the lowest intelligence quotient.

Conclusion Our pilot study showed that emergence agitation is not uncommon in patients undergoing epilepsy surgery. However, due to smaller sample size, the role of preoperative neuropsychologic profile and hippocampal volumes in predicting the pattern of emergence is inconclusive.
Association between MIS-C and Functional Gastrointestinal Disorders in Children: A Cross-Sectional Study
Authors: Uygun Hatice , Yavuz Sibel , Şahin Tarık , Erdem Nurettin , Turgut Mehmet
Published: September 2023

Objective Multisystem inflammatory syndrome in children (MIS-C) is a serious complication of coronavirus disease 2019 which causes a hyperinflammatory syndrome that can affect all organ systems. Functional gastrointestinal disorders (FGIDs) are a heterogeneous disease spectrum with unclear etiology. Today, it is known that low-grade inflammation can cause FGIDs. Our aim in this study was to investigate whether there is a higher frequency of FGID in children diagnosed with MIS-C.

Methods In this study, 48 pediatric patients diagnosed with MIS-C were evaluated for functional gastrointestinal diseases according to the Rome IV criteria at least 6 months after diagnosis. The control group consisted of 61 pediatric patients without any chronic disease.

Results In our study, the overall prevalence of FGIDs was 54.1% (n = 26) in the patient group and 22.9% (n = 14) in the control group. The difference between the groups was statistically significant (p < 0.001). The frequencies of undiagnosed abdominal pain, irritable bowel syndrome, constipation, and dyspepsia were 41.6% (n = 20), 12.5% (n = 6), 8.3% (n = 4), and 6.2% (n = 3) in the patient group, respectively. In the control group, the corresponding rates were 9.8% (n = 6), 3.2% (n = 2), 4.9% (n = 3), and 4.9% (n = 3), respectively. A significant difference was observed between the patient and control groups in terms of functional abdominal pain (p < 0.001).

Conclusion The overall frequency of FGIDs and the prevalence of functional abdominal pain were higher in MIS-C patients than in control subjects. The data from this study support the hypothesis that FGIDs are more common in patients diagnosed with MIS-C than in healthy controls.
Political economy of COVID-19: windows of opportunities and contestations in East Africa
Authors: Canwat Vincent
Published: September 2023

COVID-19 and its control measures remain contested issues in literature. While some of the literature views COVID-19 and its responses as neutral events serving the common good, other parts of the literature considers them partial events serving personal interests. This study analyses the political economy of COVID-19 in East Africa by assessing how COVID-19 and its control affected public and private policy actors and how the actors responded to them. Based on a systematic review, the study found that the pandemic and its control generated political and economic opportunities and contestations. Politically, COVID-19 and its control measures presented opportunities to suppress and oppress opposition, conduct political campaigns, provide patronage, and conduct selective enforcement. Economically, the pandemic and its responses presented opportunities to generate income and benefits for the government and its employees, businesses, and ordinary citizens. However, these opportunities were exploited to serve personal political and economic interests. COVID-19 responses also generated a lot of discontent, leading to contestations from many policy actors. The actors contested COVID-19 vaccines and science, role allocation during the response, selective enforcement of COVID-19 directives, corruption in relief provision, and the brutality of security forces. The contestations and pursuit of personal political and economic interests compromised the effectiveness of the COVID-19 response.
Collective action improves elite-driven governance in rural development within China
Authors: Li Yurui , Qin Xiaofei , Sullivan Abigail , Chi Guangqing , Lu Zhi , Pan Wei , Liu Yansui
Published: September 2023

Rural areas are at the forefront of achieving sustainable development goals, and elite actors tend to be the most influential local decision-makers in rural development. Nevertheless, improving the effectiveness of governance by elites and avoiding or redressing “elite capture” remain key challenges for sustainable rural development globally. This research integrates a large-scale quantitative dataset consisting of 604 villages in seven counties of Jiangsu province in China with qualitative data from eight villages in three out of the seven counties to examine whether and how collective action mediates the correlation between rural elites and rural development. Our quantitative analysis using multiple regression and path analysis indicates that collective action is a mediator, but it is more influential in linking governing elites than in linking economic elites with rural development. Our case studies with interviews further illuminate that collective action fuels rural development by improving resource reallocation and resource-use efficiency with the participation of both elites and non-elites. Innovative collective action designs that leverage a reputation effect to foster reciprocity norms promote the participation of elites while discouraging elite capture. Additionally, this research contributes to longstanding debates in commons governance about the role of authority interventions: we find evidence justifying the benefits of authority in catalyzing and sustaining collective action while also corroborating the critical role of democratization in improving rural governance by elites.
How does the COVID-19 pandemic influence students’ academic activities? An explorative study in a public university in Bangladesh
Authors: Saha Bijoya , Atiqul Haq Shah Md , Ahmed Khandaker Jafor
Published: September 2023

The global impact of the novel coronavirus (COVID-19) has spared no sector, causing significant socioeconomic, demographic, and particularly noteworthy educational repercussions. Among the areas significantly affected, the education systems worldwide have experienced profound changes, especially in countries like Bangladesh. In this context, numerous educational institutions in Bangladesh decided to temporarily suspend classes in situations where a higher risk of infection was perceived. Nevertheless, the tertiary education sector, including public universities, encountered substantial challenges when establishing and maintaining effective online education systems. This research uses a qualitative approach to explore the ways in which the COVID-19 pandemic has influenced the academic pursuits of students enrolled in public universities in Bangladesh. The study involved the participation of 30 students from a public university, who were interviewed in-depth using semi-structured interviews. Data analysis was conducted using thematic analysis. The findings of this study reveal unforeseen disruptions in students’ learning processes (e.g., the closure of libraries, seminars, and dormitories, and the postponement of academic and administrative activities), highlighting the complications associated with online education, particularly the limitations it presents for practical and laboratory-based learning. Additionally, a decline in both energy levels and study hours has been observed, along with an array of physical, mental, and financial challenges that directly correlate with educational activities. These outcomes emphasize the need for a hybrid academic approach within tertiary educational institutions in Bangladesh and other developing nations facing similar sociocultural and socioeconomic contexts.
Full aperture backscatter diagnostics for characterization of laser plasma instabilities at the extreme light infrastructure (ELI) beamlines
Authors: Wasser F. , Zähter Ş. , Sokol M. , Rivers M. , Atzeni S. , Condamine F. P. , Cristoforetti G. , Fauvel G. , Fischer N. , Gizzi L. A. , Hannasch A. , Hesse M. , Laštovička T. , Lutz P. , Rubovič P. , Schaumann G. , Schott N. , Singh R. L. , Theobald W. , Weber S. , Ditmire T. , Forner T. , Roth M.
Published: September 2023

We report on the commissioning of a full aperture backscatter diagnostics station for the kilojoule, nanosecond high repetition rate L4n laser operating at a wavelength of 527 nm at the Extreme Light Infrastructure (ELI) - Beamlines, Dolni Brezany, Czech Republic. Light scattered back from laser–plasma interaction into the cone of the final focusing lens is captured and split into different channels to measure the signatures of laser plasma instabilities from stimulated Brillouin scattering, stimulated Raman scattering, and two plasmon decay with respect to back scattered energy, its spectrum, and its temporal profile. The performance was confirmed in a commissioning experiment with more than 800 shots at laser intensities ranging from 0.5 × 1013 to 1.1 × 1015 W cm−2. These diagnostics are permanently installed at ELI Beamlines, and can be used to understand the details of laser–plasma interactions in experiments with kJ and 527 nm light. The large number of shots that can be collected in an experimental campaign will allow us to study the details of the laser–plasma interaction with a high level of confidence.
Flexible thin film optical solar reflectors with Ta2O5-based multimaterial coatings for space radiative cooling
Authors: Xiao Wei , Dai Peng , Singh H. Johnson , Ajia Idris A. , Yan Xingzhao , Wiecha Peter R. , Huang Ruomeng , de Groot C. H. (Kees) , Muskens Otto L. , Sun Kai
Published: September 2023

Optical Solar Reflectors (OSRs) combine low solar radiation absorption (α) and high broadband infrared emissivity (ε) and are applied to the external surface of spacecraft for its thermal management. Bulk glass OSR tiles are the incumbent, but ultra-lightweight and thin-film flexible OSR coatings are raising considerable interest for both space and terrestrial radiative cooling applications. In this work, a genetic algorithm combined with a transfer matrix method is used for the design and optimization of multimaterial thin-film OSRs for broadband radiative cooling. The algorithm simultaneously optimizes the spectral performance of the OSR at two parts of the wavelength spectrum, solar (0.3–2.5 μm) and thermal infrared (2.5–30 μm). The designed optimized OSR structure consists of 18 alternating layers of three materials, SiN, SiO2, and Ta2O5, on top of an Al mirror backreflector, with a total thickness of only 2.088 μm. The optimized multilayer stack contributes distributed Bragg reflections that reduce the residual solar absorption below that of an uncoated Al mirror. The optimized OSR is demonstrated experimentally on a 150 mm (6 in.) Si wafer and on a flexible polyimide substrate using a production level reactive sputtering tool. The fabricated thin film OSR shows good thermal-optical property with α = 0.11 and ε = 0.75 and achieves a net cooling power of 150.1 W/m2 under conditions of one sun total solar irradiance in space. The ultrathin coating fabricated using hard inorganic materials facilitates its integration onto flexible foils and enables large-scale manufacture of low-cost OSRs for broadband radiative cooling applications.
Period-doubling bifurcation in surface radio-frequency trap: Transition to chaos through Feigenbaum scenario
Authors: Rudyi S. S. , Rybin V. V. , Semynin M. S. , Shcherbinin D. P. , Rozhdestvensky Yu. V. , Ivanov A. V.
Published: September 2023

We have numerically investigated the dynamics of charged microparticles in a “five-wire” surface radio-frequency trap. The period-doubling bifurcation conditions have been shown to depend on the particle, the trap, and the alternating voltage parameters. For a comprehensive study of the dynamics chaotization through a cascade of period doubling, we have used Fourier analysis of a particle trajectory as well as the calculations of a non-trivial Lyapunov exponent map. We have demonstrated that the period-doubling bifurcation is consistent with a Feigenbaum scenario. A new approach to particle property determination can, thus, be based on observing a period-doubling bifurcation.
Flow pattern diagram of compressible non-equilibrium gas flow around a circular cylinder
Authors: Chen Fang , Liu Kun , Li Ping , Ji Lucheng
Published: September 2023

An investigation into the non-equilibrium gas flow around a circular cylinder within the Knudsen number (Kn) range of 0.001–1 and the free-stream Mach number (Ma) range of 0.01–6 is presented using the unstructured grid unified gas kinetic scheme. The primary objective is to examine the impact of Kn and Ma on flow patterns. The flow pattern diagram illustrating seven flow patterns in the Ma-Kn space is provided, including the transition boundary between bow shock-wave with laminar flow (BS+L) and bow shock-wave with vortex flow (BS+V). The relationships between Re-Kn and Ma-Re both follow the power function: y=eβxα, where α and β are constants. The study also provides a more precise critical curve of vortex shedding in subsonic inflow, the boundary of tailing shock-wave, and the boundary of vortex shedding in a transonic inflow. The flow pattern diagram indicates that the variation of flow separation with Kn is non-monotonic across the entire Ma range but is monotonic at Ma>1. In the subsonic inflow, the critical Re of flow separation (Rec) increases with Ma, while Rec initially increases and then decreases with Kn. The critical Ma at the turning point is about 0.72. In supersonic inflow, the critical Re associated with the onset of flow separation either increases or decreases with the increase in Ma or Kn. The critical Re of vortex shedding is non-monotonic with Kn. The critical Re of the trailing shock-wave decreases with both Kn and Ma. In the transonic inflow, the critical Re and critical Ma of vortex shedding decrease with Kn. As rarefaction increases, the type of flow patterns decreases. The flow pattern diagram provides a visual representation of the impact of rarefaction and compressibility effects on flow pattern transitions and assists in determining the applicable range of the drag coefficient model.
Stacking order, charge doping, and strain-induced switching between AFM and FM in bilayer GdI2
Authors: Li Shujing , Hou Yuefei , Zhou Mei , Li Menglei , Zheng Fawei , Shao Xiaohong , Zhang Ping
Published: September 2023

GdI2 monolayer is a promising material for spintronics applications due to its robust room-temperature ferromagnetism and sizable valley polarization. In two-dimensional van der Waals magnets, interlayer magnetic coupling plays a crucial role in device applications. The performance of these devices can be effectively tuned by adjusting the stacking order, charge doping, and strain. By performing first-principles calculations, we have demonstrated that the interlayer magnetic coupling in bilayer GdI2 is highly dependent on the stacking order, which can be tuned between ferromagnetic (FM) and antiferromagnetic orders through lateral shifting. Furthermore, the interlayer magnetic coupling can also be tuned by charge doping and strain, where both electron and hole doping can enhance the FM coupling interaction between layers, and the interlayer FM coupling can be strengthened with increasing biaxial tensile strain. These results show that bilayer GdI2 has rich tunable interlayer magnetic interactions, which can be used in designing interesting spin tunnel field-effect transistor devices.
Direct determination of 2D momentum space from 2D spatial coherence of light using a modified Michelson interferometer
Authors: Vedhanth S. V. U. , Datta Shouvik
Published: September 2023

Momentum space distribution of photons coming out of any light emitting material/device provides critical information about their underlying physical origin. Conventional methods of determining such properties impose specific instrumentational difficulties for probing samples kept within a low temperature cryostat. There were past studies to measure a one-dimensional coherence function, which could then be used for extracting momentum space information, as well as reports of measurements of just a two-dimensional (2D) coherence function. However, all of those are associated with additional experimental complexities. So, here we propose a simpler, modified Michelson interferometer based optical setup that is kept at room temperature and placed outside the low temperature cryostat at a distance away from it. We initially measure the 2D coherence function of emitted light, which can then be used to directly estimate the 2D in-plane momentum space distribution by calculating its fast Fourier transform. We also discuss how this experimental method can overcome instrumentational difficulties encountered in the past. Similar instrumentations can also be extended for momentum space resolved astronomical studies and telecommunications involving distant light sources.
Parameter estimation in ultrafast spectroscopy using probability theory
Authors: Harel Elad
Published: September 2023

Ultrafast spectroscopy is a powerful technique that utilizes short pulses on the femtosecond time scale to generate and probe coherent responses in molecular systems. While the specific ultrafast methodologies vary, the most common data analysis tools rely on discrete Fourier transformation for recovering coherences that report on electronic or vibrational states and multi-exponential fitting for probing population dynamics, such as excited-state relaxation. These analysis tools are widely used due to their perceived reliability in estimating frequencies and decay rates. Here, we demonstrate that such “black box” methods for parameter estimation often lead to inaccurate results even in the absence of noise. To address this issue, we propose an alternative approach based on Bayes probability theory that simultaneously accounts for both population and coherence contributions to the signal. This Bayesian inference method offers accurate parameter estimations across a broad range of experimental conditions, including scenarios with high noise and data truncation. In contrast to traditional methods, Bayesian inference incorporates prior information about the measured signal and noise, leading to improved accuracy. Moreover, it provides estimator error bounds, enabling a systematic statistical framework for interpreting confidence in the results. By employing Bayesian inference, all parameters of a realistic model system may be accurately recovered, even in extremely challenging scenarios where Fourier and multi-exponential fitting methods fail. This approach offers a more reliable and comprehensive analysis tool for time-resolved coherent spectroscopy, enhancing our understanding of molecular systems and enabling a better interpretation of experimental data.
To guess or not to guess excited state amplitudes during optimization and dynamics
Authors: Cofer-Shabica D. Vale , Athavale Vishikh , Subotnik Joseph E.
Published: September 2023

We report robust initial guesses for the amplitudes and z-vectors in a configuration interaction singles or Tamm–Dancoff approximation calculation that consistently reduce the total number of iterations required for an excited state calculation often by over 50%. The end result of these guesses is that the practicing chemist can expect to generate excited state optimized structures with a total wall time reduced by as much as 30% in the future without any approximations—simply by using information gathered at one geometry and applying it to another geometry.
Learned mappings for targeted free energy perturbation between peptide conformations
Authors: Willow Soohaeng Yoo , Kang Lulu , Minh David D. L.
Published: September 2023

Targeted free energy perturbation uses an invertible mapping to promote configuration space overlap and the convergence of free energy estimates. However, developing suitable mappings can be challenging. Wirnsberger et al. [J. Chem. Phys. 153, 144112 (2020)] demonstrated the use of machine learning to train deep neural networks that map between Boltzmann distributions for different thermodynamic states. Here, we adapt their approach to the free energy differences of a flexible bonded molecule, deca-alanine, with harmonic biases and different spring centers. When the neural network is trained until “early stopping”—when the loss value of the test set increases—we calculate accurate free energy differences between thermodynamic states with spring centers separated by 1 Å and sometimes 2 Å. For more distant thermodynamic states, the mapping does not produce structures representative of the target state, and the method does not reproduce reference calculations.
Deformation transients of confined droplets within interacting electric and magnetic field environment
Authors: Gupta Pulak , Dhar Purbarun , Samanta Devranjan
Published: September 2023

A theoretical exploration and an analytical model for the electro-magneto-hydrodynamics (EMHD) of leaky dielectric liquid droplets suspended in an immiscible confined fluid domain have been presented. The analytical solution for the system, under small deformation approximation in the creeping flow regime, has been put forward. The study of droplet deformation suggests that its temporal evolution is exponential and dependent on the electric and magnetic field interaction. Furthermore, the direction of the applied magnetic field relative to the electric field determines whether the magnetic force opposes or facilitates the interfacial net electrical force caused by the electric field. Validation of the proposed model at the asymptotic limits of vanishing magnetic field shows that the model accurately reduces to the case of the transient electrohydrodynamic model. We also propose a magnetic discriminating function (ϕM) to quantify the steady-state droplet deformation in the presence of interacting electric and magnetic fields. The change of droplets from a spherical shape to prolate and oblate spheroids corresponds to ϕM> 0 and < 0 regimes, respectively. It is shown that a substantial augmentation in the deformation parameter and the associated EMHD circulation within and around the droplet is achieved when aided by a low-magnitude magnetic field. The analysis also reveals the deformation lag and specific critical parameters that aid or suppress this lag behavior, discussed in terms of relevant non-dimensional parameters.
Nonlinear intensity dependence of ratchet currents induced by terahertz laser radiation in bilayer graphene with asymmetric periodic grating gates
Authors: Mönch E. , Hubmann S. , Yahniuk I. , Schweiss S. , Bel’kov V. V. , Golub L. E. , Huber R. , Eroms J. , Watanabe K. , Taniguchi T. , Weiss D. , Ganichev S. D.
Published: September 2023

We report on the observation of a nonlinear intensity dependence of the terahertz radiation-induced ratchet effects in bilayer graphene with asymmetric dual-grating gate lateral lattices. These nonlinear ratchet currents are studied in structures of two designs with dual-grating gates fabricated on top of boron nitride encapsulated bilayer graphene and beneath it. The strength and sign of the photocurrent can be controllably varied by changing the bias voltages applied to individual dual-grating subgates and the back gate. The current consists of contributions insensitive to the radiation’s polarization state, defined by the orientation of the radiation electric field vector with respect to the dual-grating gate metal stripes, and the circular ratchet sensitive to the radiation helicity. We show that intense terahertz radiation results in a nonlinear intensity dependence caused by electron gas heating. At room temperature, the ratchet current saturates at high intensities of the order of hundreds to several hundreds of kW cm−2. At T=4 K, the nonlinearity manifests itself at intensities that are one or two orders of magnitude lower; moreover, the photoresponse exhibits a complex dependence on the intensity, including a saturation and even a change of sign with increasing intensity. This complexity is attributed to the interplay of the Seebeck ratchet and the dynamic carrier-density redistribution, which feature different intensity dependencies and nonlinear behavior of the sample’s conductivity induced by electron gas heating. The latter is demonstrated by studying the THz photoconductivity. Our study demonstrates that graphene-based asymmetric dual-grating gate devices can be used as terahertz detectors at room temperature over a wide dynamic range, spanning many orders of magnitude of terahertz radiation power. Therefore, their integration together with current-driven read-out electronics is attractive for the operation with high-power pulsed sources.
Time series prediction of ship course keeping in waves using higher order dynamic mode decomposition
Authors: Chen Chang-Zhe , Zou Zao-Jian , Zou Lu , Zou Ming , Kou Jia-Qing
Published: September 2023

A novel reduced-order model (ROM) based on higher order dynamic mode decomposition (HODMD) is proposed for the time series prediction of ship course-keeping motion in waves. The proposed ROM is validated by using the data of course-keeping tests of an ONR tumblehome ship model. First, modes are decomposed from the model test data by standard DMD and HODMD, and the dominant modes are selected according to the energy index. Then, the decomposed dominant modes are used to reconstruct and predict the dynamics of ship motion. The dynamic characteristics in the dynamical systems are revealed according to the energy index, growth rates, and frequencies of the decomposed modes. In addition, the effects of the tunable parameter in HODMD on prediction accuracy and computational times are analyzed by a parametric study. The prediction results by HODMD show better agreement with the model test data than those by standard DMD.
Radio frequency electrical resistance measurement under destructive pulsed magnetic fields
Authors: Shitaokoshi T. , Kawachi S. , Nomura T. , Balakirev F. F. , Kohama Y.
Published: September 2023

We developed a resistance measurement using radio frequency reflection to investigate the electrical transport characteristics under destructive pulsed magnetic fields above 100 T. A sample stage consisting of a homemade flexible printed circuit reduced the noise caused by the induced voltage from the pulsed magnetic fields, improving the accuracy of the measurements of the reflected waves. From the obtained reflectance data, the absolute value of the magnetoresistance was successfully determined by analyzing the phase with admittance charts. These developments enable more accurate and comprehensive measurements of electrical resistance in pulsed magnetic fields.
Analysis of an innovative compact point absorber wave energy converter concept suitable for small-scale power applications
Authors: Vijayasankar Vishnu , Kumar Suman , Samad Abdus , Zuo Lei
Published: September 2023

In response to the need for efficient, small-scale power sources for applications such as ocean observation and navigation, this paper presents the design, modeling, fabrication, testing, and analysis of a compact point-absorber wave energy converter (PAWEC) equipped with a mechanical direct-drive power takeoff (PTO) mechanism. The motivation is to address the mismatch between the natural frequencies of conventional PAWECs and dominant ocean wave frequencies, which limits energy capture. The primary objective is to enhance the efficiency of small-scale wave energy converters (WEC) without increasing the buoy size. To achieve this, we introduce a novel design element: an added mass plate (AMP) attached to the buoy. The AMP is devised to increase the WEC added mass and natural period, thereby aligning its natural frequency with dominant ocean wave frequencies. In our case study of a scaled model (1:2.2), the AMP effectively doubled the added mass of the WEC and increased its natural period by 32%. The WEC incorporates a rack and pinion mechanical motion rectifier-type PTO to convert the heave oscillations of the buoy into unidirectional rotation. The scaled model was tested in a wave basin facility with regular waves at zero angle of incidence. The WEC with AMP achieved a maximum root mean square power of 9.34 W, a nearly 30% increase compared to the conventional configuration without AMP, which produced 7.12 W under similar wave conditions. Numerical analysis using the boundary element method in the frequency domain for regular waves confirmed these findings. Finally, it has been derived that the proposed WEC, equipped with an AMP, offers enhanced efficiency in longer wave periods without the need for a larger buoy, establishing its viability as a power source for navigational buoys. This paper also offers a comprehensive guide to experimental techniques for characterizing a PAWEC in a laboratory setting, contributing valuable insights into the wave energy community.
Horizontal to perpendicular transition of lamellar and cylinder phases in block copolymer films induced by interface segregation of single-chain nanoparticles during solvent evaporation
Authors: Qian Zhao , Shi Rui , Lu Zhong-Yuan , Qian Hu-Jun
Published: September 2023

How to fabricate perpendicularly oriented domains (PODs) of lamellar and cylinder phases in block copolymer thin films remains a major challenge. In this work, via a coarse-grained molecular dynamics simulation study, we report a solvent evaporation strategy starting from a mixed solution of A-b-B-type diblock copolymers (DBCs) and single-chain nanoparticles (SCNPs) with the same composition, which is capable of spontaneously generating PODs in drying DBC films induced by the interface segregation of SCNPs. The latter occurs at both the free surface and substrate and, consequently, neutralizes the interface selectivity of distinct blocks in DBCs, leading to spontaneous formation of PODs at both interfaces. The interface segregation of SCNPs is related to the weak solvophilicity of the internal cross-linker units. A mean-field theory calculation demonstrates that the increase in the chemical potential of SCNPs in the bulk region drives their interface segregation along with solvent evaporation. We believe that such a strategy can be useful in regulating the PODs of DBC films in practical applications.
Temperature/laser dependence of N3 optical centers in natural type Ia diamonds through photoluminescence spectroscopy
Authors: Jia Gangyuan , Zhang Yufei , Song Zhonghua , Wang Kaiyue , Huangfu Chenyang , Hao Jinchen , Wang Liang , Bai Hao
Published: September 2023

In this work, low-temperature photoluminescence spectroscopy was employed to investigate the N3 optical color center in natural type Ia diamond. The optical properties of the N3 center with regular changes in testing temperature and laser power were studied, and the energy level transition was also discussed. The results showed that the PL intensity of the N3 center enhanced sub-linearly with laser power increased, indicating that the electron transition of the N3 center was mainly radiative recombination with weak Auger recombination participation. In addition, the physical model was employed to analyze the change in the zero phonon line with the increase in the test temperature; it obtained thermal quenching activation energy (25.2 meV), bond softening, and strong interaction with acoustical phonons of the N3 center. The theoretical analysis of the broadening parameters revealed that the longitudinal optical phonon energy was 55.1 meV, and the electron–optic phonon coupling strength was 2.3 meV.
A deep learning framework for solving forward and inverse problems of power-law fluids
Authors: Zhai Ruizhi , Yin Deshun , Pang Guofei
Published: September 2023

We for the first time leverage deep learning approaches to solve forward and inverse problems of two-dimensional laminar flows for power-law fluids. We propose a deep-learning framework, called Power-Law-Fluid-Net (PL-Net). We develop a surrogate model to solve the forward problems of the power-law fluids, and solve the inverse problems utilizing only a small set of measurement data under the assumption that boundary conditions (BCs) can be partially known. In the design of the methods, we incorporate the hard boundary condition constraints to accelerate the iteration of stochastic gradient descent methods for minimizing loss functions. For the forward problems, by incorporating the constitutive parameters into the input variables of neural networks, the PL-Net serves as a surrogate model for simulating the pressure-driven flows inside pipes having cross sections of varying shapes. We investigate the influences of the BC type, activation function type, and number of collocation points on the accuracy of numerical solutions. For the inverse problems, the PL-Net infers the physical quantities or constitutive parameters from a small number of measurements of flow field variables. The BCs of the inverse problems can even be partially known. We demonstrate the effects of BC type, number of sensors, and noise level on accuracy of inferred quantities. Computational examples indicate the high accuracy of the PL-Net in tackling both the forward and inverse problems of the power-law fluids.
Stochastic cooling notch filter developments for the high-precision spectrometer ring in the high intensity heavy-ion accelerator facility project
Authors: Zhu Guangyu , Wu Junxia , Yin Jia , Wei Yuan , He Peilin , Du Ze , Ma Liyao , Qiu Zishuai , Zhang Zhaolong , Yang Jiancheng
Published: September 2023

Stochastic cooling of the high-precision spectrometer ring (SRing) at the High Intensity Heavy-Ion Accelerator Facility (HIAF) project in China, which is used mainly for experiments with radioactive fragment beams, is applied to speed up the cooling process of a stored ion beam. In this article, a new coaxial-type notch filter with an amplitude equalizer in the long branch and an optical-type notch filter with phase-stabilized optical fiber are discussed and evaluated for the SRing stochastic cooling system. Both prototypes of coaxial and optical notch filters are fabricated and tested. The minimum notch depth of coaxial and optical notch filters reaches to 26 and 40 dB, respectively. The performance of both coaxial notch filter and optical fiber notch filter is presented in this work. These developments will be used not only for the longitudinal stochastic cooling system but also have potential for the beam feedback system.
Anisotropic particle multiphase equilibria in nonuniform fields
Authors: Baron Philippe B. , Hendley Rachel S. , Bevan Michael A.
Published: September 2023

We report a method to predict equilibrium concentration profiles of hard ellipses in nonuniform fields, including multiphase equilibria of fluid, nematic, and crystal phases. Our model is based on a balance of osmotic pressure and field mediated forces by employing the local density approximation. Implementation of this model requires development of accurate equations of state for each phase as a function of hard ellipse aspect ratio in the range k = 1–9. The predicted density profiles display overall good agreement with Monte Carlo simulations for hard ellipse aspect ratios k = 2, 4, and 6 in gravitational and electric fields with fluid–nematic, fluid–crystal, and fluid–nematic–crystal multiphase equilibria. The profiles of local order parameters for positional and orientational order display good agreement with values expected for bulk homogeneous hard ellipses in the same density ranges. Small discrepancies between predictions and simulations are observed at crystal–nematic and crystal–fluid interfaces due to limitations of the local density approximation, finite system sizes, and uniform periodic boundary conditions. The ability of the model to capture multiphase equilibria of hard ellipses in nonuniform fields as a function of particle aspect ratio provides a basis to control anisotropic particle microstructure on interfacial energy landscapes in diverse materials and applications.
Spatial–temporal analysis of magnetohydrodynamics flow and energy flux of power-law nanofluid in a confined domain
Authors: Nishad Surabhi , Bhargava Rama , Nayak Ameeya Kumar , Weigand Bernhard
Published: September 2023

Energy flux analysis of power-law fluid is a novel contribution to recent developments in computational fluid dynamics. The study of the unsteady two-dimensional flow with double diffusive effect inside a complex enclosure exhibits great potential in optimizing the heat transfer rate due to the wavy nature of the side walls. The enclosure is confined with the flow circulation due to the thermal and solutal gradients acting along the left and right wavy walls. The computational time and accuracy in results are estimated and compared by implementing the finite volume method and element-free Galerkin technique. The results are obtained in terms of streamlines, isotherms, isoconcentrations, average Nusselt number, Sherwood number, and total entropy generation due to the effect of conventional parameters, namely, power-law index, Rayleigh number, buoyancy ratio parameter, thermophoresis parameter, Brownian motion parameter, and Lewis number with a fixed Prandtl number throughout the computation. The optimized double-diffusive natural convection analysis is based on entropy generation and a calculated Bejan number. The novelty of this paper lies in the implementation of a mesh-free approach, which may be useful for the further analysis of elliptical/semi-elliptical structures.