Density Modulation Research Articles

Engineering phase and density of Bose–Einstein condensates in curved waveguides with toroidal topology

We investigate the effects of ellipticity-induced curvature on atomic Bose–Einstein condensates confined in quasi-one-dimensional closed-loop waveguides. Our theoretical study reveals intriguing phenomena arising from the interplay between curvature and interactions. Density modulations are observed in regions of high curvature, but these modulations are suppressed by strong repulsive interactions. Additionally, we observe phase accumulation in regions with the lowest curvature when the waveguide with superflow has high eccentricity. Furthermore, waveguides hosting vortices exhibit dynamic transformations between states with different angular momenta. These findings provide insights into the behavior of atomic condensates in curved waveguides, with implications for fundamental physics and quantum technologies. The interplay between curvature and interactions offers opportunities for exploring novel quantum phenomena and engineering quantum states in confined geometries.

Modulation of electronic density in ultrathin g-C3N4 for enhanced photocatalytic hydrogen evolution through an efficient hydrogen spillover pathway

The high recombination of photoinduced electron-hole and deep charge trapping in graphitic carbon nitride (g-C3N4)-based photocatalysts have limited the photocatalytic activity in hydrogen evolution reaction (HER). Here, we proposed the synergistic strategies of electron-deficient boron (B) and electron-rich phosphorus (P) doped g-C3N4 (BPCN) through tuning the electron density for enhanced photocatalytic activity in HER under visible light irradiation. The BPCN exhibited highest photocatalytic activity in HER with the apparent quantum efficiency of 17.4% at 400 nm superior to reported g-C3N4-based photocatalysts. The remarkable activity in HER was attributed to the efficient charge separtion by the shallow charge capture, electron transfer from P to B and the efficient hydrogen spillover pathway occurred by the strong absorption H2O at P sites and then H transferring to B sites. This work paves a new route to changing the electronic density with the tunable band structures through the doping engineering for enhanced photocatalytic activity.

Point-Contact Bonding of Integrated Three-Dimensional Manifold Microchannel Cooling Within Direct Bonded Copper Platform

Abstract A microchannel heat sink integrated with a three-dimensional manifold using direct bonded copper (DBC) is promising for high power density electronics due to the combination of low thermal resistance and reduced pressure drop. However, this requires much progress on the fabrication and high-quality point-contact bonding processes of the microchannel substrate and three-dimensional manifold DBCs. In this study, we have developed processing techniques for surface preparations and high-quality point-contact solder bonding between the two DBC substrates. We utilized chemical polishing followed by electroless plating to prevent excess solder from blocking the microchannels. We performed a parametric study to investigate the impact of bonding time and surface roughness on the tensile strength of the bonding interface. The bonding strength increased from 1.8 MPa to 2.3 MPa as the bonding time increased from 10 to 30 min while reducing the surface roughness from Rz = 0.21 to 0.05 μm, resulting in increasing the bonding strength from 0.16 MPa to 2.07 MPa. We successfully tested the microcooler up to the inlet pressure of 70 kPa and pressure drop of 30 kPa, which translates to the tensile strength at the bonding point contacts, which remains well below the 2.30 MPa. We achieved the junction-to-coolant thermal resistance of 0.2 cm2 K/W at chip heat flux of 590 W/cm2. Thus, our study provides an important proof-of-concept demonstration toward enabling high power density modules for power conversion applications.

Understanding Effects of Alkyl Side-Chain Density on Polaron Formation Via Electrochemical Doping in Thiophene Polymers.

Polarons exist when charges are injected into organic semiconductors due to their strong coupling with the lattice phonons, significantly affecting electronic charge-transport properties. Understanding the formation and (de)localization of polarons is therefore critical for further developing organic semiconductors as a future electronics platform. However, there are very few studies reported in this area. In particular, there is no direct in situ monitoring of polaron formation and identification of its dependence on molecular structure and impact on electrical properties, limiting further advancement in organic electronics. Herein, how a minor modification of side-chain density in thiophene-based conjugated polymers affects the polaron formation via electrochemical doping, changing the polymers' electrical response to the surrounding dielectric environment for gas sensing, is demonstrated. It is found that the reduction in side-chain density results in a multistep polaron formation, leading to an initial formation of localized polarons in thiophene units without side chains. Reduced side-chain density also allows the formation of a high density of polarons with fewer polymer structural changes. More numerous but more localized polarons generate a stronger analyte response but without the selectivity between polar and non-polar solvents, which is different from the more delocalized polarons that show clear selectivity. The results provide important molecular understanding and design rules for the polaron formation and its impact on electrical properties.

Effect of post-treatment on photocatalytic activity of anodic titania photonic crystals

One of the possible ways to enhance photocatalytic activity is the use of photonic band gap (PBG) materials. Anodic titania photonic crystals (PhCs) are promising PBG structures, whose structure can be tuned easily by anodizing conditions. However, the effect of various doping approaches on the photocatalytic activity of anodic titania PhCs has never been studied before. Here anodic titania PhCs were synthesized by cycling anodizing of titanium with voltage versus charge density modulation followed by annealing at 450 °C in air. The PhCs were post-treated by electrochemical reduction in 0.1 M Na2SO4, annealing in H2/Ar mixture or NH3. The phase composition and structure of titania PhCs were studied by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, and electron paramagnetic resonance spectroscopy. Photocatalytic activity of PhCs in the degradation of the methylene blue dye decreases after electrochemical reduction and annealing in NH3, whereas the annealing in H2/Ar at 600 °C for 2 h leads to an increase in the degradation rate constant by 60%.

Friedel oscillation in non-Fermi liquid: lesson from exactly solvable Hatsugai–Kohmoto model

When non-magnetic impurity immerses in Fermi sea, a regular modulation of charge density around impurity will appear and such phenomena is called Friedel oscillation (FO). Although both Luttinger liquid and Landau Fermi liquid show such characteristic oscillation, FO in generic non-Fermi liquid (NFL) phase is still largely unknown. Here, we show that FO indeed exists in NFL state of an exactly solvable model, i.e. the Hatsugai–Kohmoto model which has been intensively explored in recent years. Combining T-matrix approximation and linear-response-theory, an interesting picture emerges, if two interaction-induced quasi-particles bands in NFL are partially occupied, FO in this situation is determined by a novel structure in momentum space, i.e. the ‘average Fermi surface’ (average over two quasi-particle Fermi surface), which highlights the inter-band particle-hole excitation. We hope our study here provides a counterintuitive example in which FO with Fermi surface coexists with NFL quasi-particle, and it may be useful to detect hidden ‘average Fermi surface’ structure in other correlated electron systems.

Suppressing thermal runaway propagation of nickel-rich Lithium-ion battery modules using silica aerogel sheets

Suppressing thermal runaway (TR) propagation within Lithium-ion battery (LIB) modules/packs/systems is one of the key factors to ensure the safety utilization of electric vehicles and energy storage systems. This contribution aims at introducing Silica Aerogel Sheets (SAS) into high energy density modules to suppress the TR propagation. The SAS, synthesized via a sol-gel process followed by supercritical fluid drying, possess almost an ideal thermal insulator characteristic due to the low thermal conductivity of 0.020 W/(m·K) at room temperature. The SAS are inserted between two adjacent pouch cells (LiNi0.86Co0.07Mn0.07O2/graphite, 320 Wh.kg−1) to assemble high energy density modules. A single pouch cell, subjected to the TR test with an Accelerating Rate Calorimetry, releases a huge amount of heat energy (1083 kJ/kg) with the maximum temperature beyond 800 °C. In the open area test site for TR propagation experiments, it can be observed that violent jet and flame burst from the cell, which is designed to undergo TR first and trigger the TR propagation of the modules. The results show that only one single layer of SAS cannot stop the TR propagation or fire spreading. However, more layers of SAS (three in the experiments) can successfully suppress the TR propagation and block fire progression. The temperature of the adjacent cell only reaches 105.4 °C. Therefore, the SAS with acceptable thickness can suppress the TR propagation successfully to improve the safety of the LIB modules.

Two decades of carbon dynamics in an actively-managed, naturally-regenerated longleaf/slash pine forest

Naturally regenerated pine ecosystems cover 11.7 Mha of the southeastern United States, comprising 13.8% of the forested land, and represent an important component in the carbon balance for the region. These forests are exposed to strong climatic variability from extreme multiyear droughts to above average precipitation years, many are actively managed with prescribed fire and some modification of tree density by cutting. This study is unique in assessing the effects of management and climatic variability for two decades on the carbon (C) dynamics and long-term net ecosystem C balance (NECB) for an actively-managed naturally regenerated pine ecosystem. We used 21 years of eddy covariance estimates of net ecosystem C production (NEP), combined with periodic tree inventories, understory biomass and forest floor assessments. Forest management included six prescribed fire cycles on a three-year rotation beginning in the third year of the study, and a preparatory cut which reduced basal area by 20% from 17.05 ± 0.66 m2/ha during the spring of 2016. The mean annual NEP was 3.32 ± 1.37 Mg C/ha yr−1, with a range of 5.35 Mg C/ha (1.30 to 6.65 Mg C ha/yr), was not significantly affected by fire and was mainly controlled by water availability. A combination of aboveground C assessments (tree and understory) and NEP indicates that C stored belowground accounted for 23% of NEP, with part of this used to support aboveground understory growth after fire. Net ecosystem carbon balance (NECB, integrated NEP and C losses from management) fluctuated in a range of 15.5 Mg Cha−1 (6.7 to −8.8 Mg C ha -1) and was sensitive to management. However, a higher NECB during the second decade than in the first (15.3 Mg C/ha vs. 2.7 Mg C/ha) reflected increased NEP (40 Mg C/ha vs. 25.4 Mg C/ha) as it responded to a greater water availability, despite similar amounts of C lost from management activities during both decades. At the end of the 21 years study, the ecosystem had incorporated 22.6 Mg C ha -1, indicating that actively managed naturally regenerated pine ecosystems in the region can mitigate C dioxide emissions under a broad range of climatic conditions, reduce wildfire risks, while providing numerous ecosystem services.

Quantum droplets in one-dimensional Bose-Bose mixtures: beyond the Lee-Huang-Yang description

The static and dynamic properties of self-bound quantum droplets in a one-dimensional Bose-Bose mixture are discussed in the spirit of the Hartree–Fock-Bogoliubov theory. This latter enables us to provide beyond the Lee-Huang-Yang (LHY) quantum corrections to the equation of state at both zero and finite temperatures. In the uniform case our results for the ground-state energy and the critical temperature are confirmed through comparison with Quantum Monte-Carlo simulation and with available theoretical results. The density profiles are supported by numerical simulations of the generalized Gross-Pitaevskii equation which selfconsistently includes higher-order terms originating from the normal and anomalous fluctuations under the local density approximation. We show that the density exhibits a dip near its center in the flat-top plateau region for large interspecies interactions. We exemplify the impact of the beyond LHY corrections on the spatiotemporal evolution of the self-bound droplet in the presence of excitation induced by periodic density modulation. It is found that higher-order corrections may lead to the formation of a train of small droplets. We then extend our study for the case of inhomogeneous droplets in quasi one-dimensional Bose mixtures.

Sigma-Delta Modulation on a Three-Phase Four-Leg VSI to Eliminate the Common Mode Voltage and Comply With the Military Standards

This paper demonstrates sigma-delta pulse density modulation (PDM) without common mode voltage on a four-leg voltage source inverter designed as a grid-forming inverter. Using PDM ensures that switching updates occur simultaneously for all phases and sigma-delta modulation is the most advantageous PDM for this application. The converter does not produce common mode voltage in the switching frequency range, thus meeting the conducted electromagnetic interference limits in MIL-STD-461G without the need for a large common mode choke. Further, the proposed common mode elimination method does not degrade the output voltage power quality, which meets the requirements in MIL-STD-1399 section 300 part I for type 1 voltage. The practical implementation of the control system on a Field Programmable Gate Array (FPGA) is presented and compliance with the two military standards is demonstrated on a laboratory prototype built with SiC MOSFETs.

Reduction of Spurious Switching in Direct Vector Quantized Space Vector Pulse Density Modulation Scheme for Multilevel Inverters

A generalized online switching scheme for multi-level inverter based on Direct Vector Quantized Space Vector Pulse Density Modulation (DVQSVPDM) suitable for adjustable speed drive is proposed in this article. The existing DVQSVPDM schemes have spurious switching as the voronoi region is determined from integrated error vector of Sigma Delta Modulator (SDM). This results in high Total Harmonic Distortion (THD) of Common Mode Voltage (CMV) at lower modulation index. In the proposed DVQSVPDM the nearest three space vectors to the reference vector forms the triangular voronoi region. The integrated error vector of SDM is quantized to its nearest space vector in the voronoi region to generate the switching vectors. This reduces spurious switching associated with DVQSVPDM schemes and improves the performance at lower modulation index by reducing THD of CMV. The proposed scheme works for all n-level inverter topologies and the computations required remain same irrespective of level of inverter. Redundant states of switching vectors are not considered for switching which results in the discontinuous nature of proposed scheme. The performance of proposed DVQSVPDM is compared with space vector based modulation schemes and third harmonic injected sine PWM scheme and the results are presented. The proposed scheme is experimentally validated for a 3hp open end winding induction motor fed with three-level inverters on both sides.

Insight into Controlled Surface Passivation of PEDOT:PSS for Defect Density Modulation and Efficient Charge Transport for Perovskite Solar Cells

Insight into Controlled Surface Passivation of PEDOT:PSS for Defect Density Modulation and Efficient Charge Transport for Perovskite Solar Cells

Wide-range and area-selective threshold voltage tunability in ultrathin indium oxide transistors

The scaling of transistors with thinner channel thicknesses has led to a surge in research on two-dimensional (2D) and quasi-2D semiconductors. However, modulating the threshold voltage (VT) in ultrathin transistors is challenging, as traditional doping methods are not readily applicable. In this work, we introduce a optical-thermal method, combining ultraviolet (UV) illumination and oxygen annealing, to achieve broad-range VT tunability in ultrathin In2O3. This method can achieve both positive and negative VT tuning and is reversible. The modulation of sheet carrier density, which corresponds to VT shift, is comparable to that obtained using other doping and capacitive charging techniques in other ultrathin transistors, including 2D semiconductors. With the controllability of VT, we successfully demonstrate the realization of depletion-load inverter and multi-state logic devices, as well as wafer-scale VT modulation via an automated laser system, showcasing its potential for low-power circuit design and non-von Neumann computing applications.

Optical coherence tomography angiography analysis of changes in the retina and the choroid after hemodialysis for end stage kidney disease.

To study effects of hemodialysis (HD) on retinal and choroidal vasculature in patients with end-stage kidney disease (ESKD) using optical coherence tomography angiography (OCTA). In this prospective study, we investigated eyes of patients undergoing hemodialysis for ESKD from Mondor University Hospital. Only one eye/patient was considered. Subfoveal choroidal thickness (SCT) was measured on enhanced-depth imaging optical coherence tomography (EDI-OCT) before and after the hemodialysis session. OCTA was used to extract retinal vascular density (superficial and deep capillary plexus, SCP, DCP) and choriocapillaris non-perfusion. Clinical, demographic and biological parameters (Blood B-Nitric Peptid rate prior to HD session) were reviewed. Twenty patients (mean age 53.2 ± 13.6years, 10 males and 10 females) were included in this prospective study. SCT significantly decreased after the HD session (234.3 ± 56.14µm before HD to 211.9 ± 60.79µm after hemodialysis (Wilcoxon signed-rank test, p = 0.003)). Non-perfusion in the choriocapillaris significantly increased after HD (41.65 ± 3.58 before HD, 42.95 ± 3.19 after HD, p = 0.036) while no significant modification of the vascular density was observed in the retinal vasculature (SCP, DCP) around the macular zone or the optic nerve. An increased plasma B-Nitric Peptide (BNP) level prior to the onset of the HD session was significantly correlated with the decrease of the SCT (r = 0.45, p = 0.043). Hemodialysis in patients with ESKD is associated with a significant decrease in SCT and an increase in non-perfusion in the choriocapillaris on OCTA. A High BNP level prior to the onset of the hemodialysis appears to be correlated with the decrease in SCT.

Modification of Bulk Density, Flow Property and Crystallinity of Microcrystalline Cellulose Prepared from Waste Cotton.

The most affordable type of tablet is the immediately compressible tablet, which uses microcrystalline cellulose (MCC), a popular pharmaceutical excipient, as a filler or binder. To make it compatible with different active drugs and excipients, we tried to change some physical properties of the MCC. In the current study, we used a chelating agent to pretreat the waste cotton before pulping, bleaching, and finally, hydrochloric acid degradation with a concentration of 2N at 100 °C temperature for 20 min to prepare MCC. The prepared MCC was treated with different concentrations of sodium hydroxide at room temperature or at -20 °C followed by precipitation with hydrochloric acid or ethanol with complete washing with distilled water till neutralization. Evaluation of the degree of polymerization (DP) and FT-IR spectrum confirm the identity of the microcrystalline cellulose. The DP was found to be 216. The bulk density of the unmodified MCC was 0.21 while that of modified MCC varied from 0.253 to 0.594. The modified MCC powder showed good flow properties compared to the unmodified MCC as evaluated by the Hausner index, Carr's index and the angle of repose. The scanning electron microscopy (SEM) of the MCC revealed that the rod shape has been changed to an oval shape due to treatment with sodium hydroxide at -20 °C. The X-ray crystallographic (XRD) analysis indicated that the unmodified MCC and standard MCC showed the crystallinity index (CrI) value of 86.82% and 87.63%, respectively, while the value ranges from 80.18% to 60.7% among the modified MCC powder. The differences in properties of the MCC might be due to the variation of rearrangement of the cellulose chain among the MCC particles due to treatment with different concentrations of a base at different temperatures and precipitation environments. This has enabled us to prepare MCC with different properties which might be compatible with different drugs.

Direct density modulation of photo-assisted field emission from an RF cold cathode

This paper explores direct density modulation of high-current electron beam emission from an RF cold cathode using optical excitation. We theoretically study the photo-assisted field emission of periodically bunched electron beams of various pulse shapes under the combined excitation of an RF field and an optical field, using an exact quantum model. Both continuous-wave (CW) and pulsed optical fields are considered. The emission current pulse amplitude, pulse width, electron number density per pulse, as well as pulse shape and its harmonic contents are investigated in detail. For CW photon sources in the UV to NIR range (i.e., 200–1200 nm), increasing the optical intensity under an RF bias tends to change the current pulse from a Gaussian to sinusoidal-like shape, thus offering strong flexibility to control the frequency components in beam current emission. Pulsed photon sources combined with an RF field can produce sharp, high-current electron bunches with pulse duration comparable with or even less than that of the optical pulse. A contour map of the density modulation depth is constructed for different combinations of RF and laser fields. The results provide insight into unlocking new opportunities to achieve direct density modulation during electron current emission by optical means.

Tuning Methylation-Dependent Silencing Dynamics by Synthetic Modulation of CpG Density.

Methylation of cytosines in CG dinucleotides (CpGs) within promoters has been shown to lead to gene silencing in mammals in natural contexts. Recently, engineered recruitment of methyltransferases (DNMTs) at specific loci was shown to be sufficient to silence synthetic and endogenous gene expression through this mechanism. A critical parameter for DNA methylation-based silencing is the distribution of CpGs within the target promoter. However, how the number or density of CpGs in the target promoter affects the dynamics of silencing by DNMT recruitment has remained unclear. Here, we constructed a library of promoters with systematically varying CpG content, and analyzed the rate of silencing in response to recruitment of DNMT. We observed a tight correlation between silencing rate and CpG content. Further, methylation-specific analysis revealed a constant accumulation rate of methylation at the promoter after DNMT recruitment. We identified a single CpG site between TATA box and transcription start site (TSS) that accounted for a substantial part of the difference in silencing rates between promoters with differing CpG content, indicating that certain residues play disproportionate roles in controlling silencing. Together, these results provide a library of promoters for synthetic epigenetic and gene regulation applications, as well as insights into the regulatory link between CpG content and silencing rate.

Entropy of coupled Klein-Gorden Field in FLRW space

The coupled Klein-Gordan (KG) field in FLRW space-time has been further studied to explore its effect on entropy. The modifications in pressure and density and hence entropy due to coupling have been calculated. There is an indication seen that the introduction of the coupling contributes to the generation of entropy in the KG field which may probably explain the large entropy of the universe.

A dichoptic advantage for detecting out-of-phase modulations of density and contrast

A dichoptic advantage for detecting out-of-phase modulations of density and contrast

Emergence of tunable periodic density correlations in a Floquet–Bloch system

In quantum gases, two-body interactions are responsible for a variety of instabilities that depend on the characteristics of both trapping and interactions. These instabilities can lead to the appearance of new structures or patterns. We report on the Floquet engineering of such a parametric instability, on a Bose-Einstein condensate held in a time-modulated optical lattice. The modulation triggers a destabilization of the condensate into a state exhibiting a density modulation with a new spatial periodicity. This new crystal-like order, which shares characteristic correlation properties with a supersolid, directly depends on the modulation parameters: The interplay between the Floquet spectrum and interactions generates narrow and adjustable instability regions, leading to the growth, from quantum or thermal fluctuations, of modes with a density modulation noncommensurate with the lattice spacing. This study demonstrates the production of metastable exotic states of matter through Floquet engineering and paves the way for further studies of dissipation in the resulting phase and of similar phenomena in other geometries.