Miracle-dz/UniFAR-FTUs huggingface dataset:
Relativistic gyratons in asymptotically AdS spacetime

The gravitational field created by beams of radiation, and pulses of light has been studied intensively since a pioneer paper by Tolman [1] who found the solution of gravitational equations in linear approximation. The exact solutions of the Einstein equations for the pencil of light has been found by Peres [2, 3] and Bonnor [4]. The gravitational field of a spinning beam-pulse of finite duration, a gyraton, generalizes these solutions to the case when the beam-pulse carries an angular momentum [5, 6]. A typical example of a gyraton would be a pulse of a circular polarized light or a modulated beam of ultrarelativistic particles with a spin. The gravitational field of the gyraton is parametrized by a number of arbitrary functions of the retarded time u. These functions arise through the dependence on u of the coefficients in mode expansion of the gravitational field. They describe profiles of the energy density and angular momenta distributions of the gyraton propagating in an asymptotically flat D-dimensional spacetime. The gyraton solutions in asymptotically flat spacetimes belong to a general class of pp-waves. In the limit of an infinitesimally short impulse and zero angular momentum the solutions describes a gravitational field of an ultrarelativistic particle - a gravitational shock wave [7]. In this paper we generalize results for gyratons in asymptotically flat spacetime [5, 6] to the case when a spacetime is asymptotically AdS. That is, we obtain exact solutions for the geometry of the gyraton propagating in an asymptotically AdS background. For zero angular momentum these solutions belong to the type of Siklos spacetimes [8] generalized to higher dimensions. In the limit of a δ(u)-like impulse these solutions correspond to gravitational shock waves in AdS spacetime. Similar to shock waves in a flat spacetime the solutions can be derived using an infinite boost of the gravitational field of a
Parameter Estimation of a Noisy Real Sinusoid Using Quartic Polynomial Approach

An analytical polynomial expression, for accurate and computationally efficient frequency estimation of a single real sinusoid under Additive White Gaussian Noise (AWGN), is derived and proposed in this paper. The method, which can be easily adapted for real time frequency estimation, is based on transforming the frequency estimation problem as the solution of a fourth order (quartic) expressed as powers of a trigonometric function containing the unknown frequency. The coefficients of the quartic polynomial can be found using the complex magnitudes of three Discrete Fourier Transform (DFT) bins, centered at the maximum magnitude value of the DFT coefficients. Simulated results illustrate that, the performance of the proposed estimator has a mean squared-error (MSE) performance which is very close to the Cramer Rao Lower Bound (CRLB) for high signal-to-noise ratio (SNR) region, as well as close to previously published estimators in the low SNR region.
Eclipsing spotted giant star with K2 and historical photometry

Context. Stars can maintain their observable magnetic activity from the pre-main sequence (PMS) to the tip of the red giant branch. However, the number of known active giants is much lower than active stars on the main sequence (MS) since the stars spend only about 10% of their MS lifetime on the giant branch. Due to their rapid evolution it is difficult to estimate the stellar parameters of giant stars. A possibility for obtaining more reliable stellar parameters for an active giant arises when it is a member of an eclipsing binary system. Aims. We have discovered EPIC 211759736, an active spotted giant star in an eclipsing binary system during the Kepler K2 Campaign 5. The eclipsing nature allows us to much better constrain the stellar parameters than in most cases of active giant stars. Methods. We have combined the K2 data with archival HATNet, ASAS, and DASCH photometry, new spectroscopic radial velocity measurements, and a set of follow-up ground-based BVRCIC photometric observations, to find the binary system parameters as well as robust spot models for the giant at two different epochs. Results. We determined the physical parameters of both stellar components and provide a description of the rotational and long-term activity of the primary component. The temperatures and luminosities of both components were examined in the context of the Hertzsprung–Russell diagram. We find that both the primary and the secondary components deviate from the evolutionary tracks corresponding to their masses in the sense that the stars appear in the diagram at lower masses than their true masses. Conclusions. We further evaluate the proposition that traditional methods generally result in higher masses for active giants than what is indicated by stellar evolution tracks in the HR diagram. A possible reason for this discrepancy could be a strong magnetic field, since we see greater differences in more active stars.
Spontaneous versus Piezoelectric Polarization in III–V Nitrides: Conceptual Aspects and Practical Consequences

Macroscopic polarization plays a major role in determining the optical and electrical properties of nitride nanostructures via polarization-induced built-in electrostatic fields. While currently fashionable, this field of endeavour is still by far in its early infancy. Here we contribute some clarifications on the conceptual issues involved in determining built-in fields in III–V nitride nanostructures, sorting out in particular the roles of spontaneous and piezoelectric polarization.
Magnetic structure of the reconnection layer and core field generation in plasmoids

Plasmoids/flux ropes have been observed both at Earth's magnetopause as well as in the magnetotail. Magnetic field measurements of such structures often reveal that rather than a minimum in field strength at their centers as expected from a simple O-type neutral line picture, they exhibit a strong core field. To address this issue, two-dimensional (2-D) and 3-D hybrid simulations are used to investigate the magnetic structure of reconnection layer in general and the formation of the core field within plasmoids in particular. The reconnection layer in the magnetotail is found to be unstable to the fire hose instability. As a result, the region between the lobe and the central plasma sheet is nearly at the marginal fire hose condition. The magnetic signatures of single and multiple X line geometries are contrasted, and it is shown that the interaction of outflowing jets from neighboring X lines leads in general to a highly complex magnetic structure within a plasmoid. The large observed core fields are explained in terms of Hall-generated currents which can naturally lead to core field strengths that even exceed the ambient lobe field in magnitude. Ion beta and the presence of a preexisting guide field are two important factors controlling the Hall-generated fields. In particular, it is shown that the presence of the small ubiquitous cross-tail field component in the magnetotail can under certain conditions lead to a strong unipolar plasmoid core field. There exist significant differences between core fields associated with plasmoids at the magnetopause and those in the tail. This is due to (1) high plasma beta in the magnetosheath and (2) the asymmetry in plasma density across the magnetopause. The former leads to smaller core fields at the magnetopause, whereas the latter leads to differences in the polarity and structure of core fields within magnetopause and magnetotail plasmoids. Such differences are illustrated through examples.
Globular clusters in the outer halo of M 31

In this paper, we present photometry of 53 globular clusters (GCs) in the M 31 outer halo, including the GALEX far-ultraviolet (FUV) and near-ultraviolet (NUV), SDSS ugriz, 15 intermediate-band filters of BATC, and 2MASS JHKs bands. By comparing the multicolour photometry with stellar population synthesis models, we determine the metallicities, ages, and masses for these GCs, aiming to probe the merging/accretion history of M 31. We find no clear trend of metallicity and mass with the de-projected radius. The halo GCs younger than ∼8 Gyr are mostly located at the de-projected radii around 100 kpc, but this may be due to a selection effect. We also find that the halo GCs have consistent metallicities with their spatially associated substructures, which provides further evidence of the physical association between them. Both the disc and halo GCs in M 31 show a bimodal luminosity distribution. However, we should emphasise that there are more faint halo GCs which are not seen in the disc. The bimodal luminosity function of the halo GCs may reflect a different origin or evolution environment in their original hosts. The M 31 halo GCs include one intermediate metallicity group (−1.5 < [Fe/H] < −0.4) and one metal-poor group ([Fe/H] < −1.5), while the disc GCs have one metal-rich group more. There are considerable differences between the halo GCs in M 31 and the Milky Way (MW). The total number of GCs in M 31 is approximately three times greater than in the MW, however M 31 has about six times more halo GCs than the MW. Compared to the halo GCs of M 31, those of the MW are mostly metal-poor. Both the numerous halo GCs and the higher-metallicity component are suggestive of an active merger history of M 31.
Emotional state and its impact on voice authentication accuracy

The paper deals with the increasing accuracy of voice authentication methods. The developed algorithm first extracts segmental parameters, such as Zero Crossing Rate, the Fundamental Frequency and Mel-frequency cepstral coefficients from voice. Based on these parameters, the neural network classifier detects the speaker's emotional state. These parameters shape the distribution of neurons in Kohonen maps, forming clusters of neurons on the map characterizing a particular emotional state. Using regression analysis, we can calculate the function of the parameters of individual emotional states. This relationship increases voice authentication accuracy and prevents unjust rejection.
Microbicide Containing Ellagic Acid Can Inhibit HIV-1 Infection

Objectives: Ellagic acid (EA) has a wide range of biological effects. The purpose of this study was to investigate the in vitro effects of EA on HIV-1 replication, viral enzyme activity and cytokine secretion by infected cells. Methods: The anti-HIV-1 activity of EA in solution was determined in vitro using the infection of TZM-bl cells by the nano luciferase-secreting R5-tropic JRCSF strain of HIV-1, which allows for the quantification of viral growth by measuring nano luciferase in the culture supernatants. The effect of EA on the cytokine secretion of TZM-bl cells was determined by a multiplexed bead array after 48 h of HIV-1 exposure. The antiviral effect of EA in the gel formulation (Ellagel), as would be used for vaginal application, was investigated by the inhibition of infection of UC87.CD4. CCR5 cells with R5-tropic pBaLEnv-recombinant HIV-1. Results: EA in solutions of up to 100 µM was not toxic to TZM-bl cells. EA added either 1 h before or 4 h after HIV-1 exposure suppressed the replication of R5-tropic HIV-1 in TZM-bl cells in a dose-dependent manner, with up to 69% inhibition at 50 µM. EA-containing solutions also exhibited a dose-dependent inhibitory effect on HIV-1 replication in U87 cells. When EA was formulated as a gel, Ellagel containing 25 µM and 50 µM EA inhibited HIV-1 replication in U87 cells by 56% and 84%, respectively. In assays of specific HIV-1 enzyme activity, Ellagel inhibited HIV-1 integrase but not protease. EA did not significantly modulate cytokine secretion. Conclusions: We conclude that EA either in solution or in a gel form inhibits HIV infection without adverse effects on target cells. Thus, gel containing EA can be tested as a new microbicide against HIV infection.
Development of a force-field-based control strategy for an upper-limb rehabilitation robot

Abstract. Robot-assisted rehabilitation has proven to be effective for improving the motor performance of patients with neuromuscular injuries. The effectiveness of robot-assisted training directly depends on the control strategy applied in the therapy training. This paper presents an end-effector upper-limb rehabilitation robot for the functional recovery training of disabled patients. A force-field-based rehabilitation control strategy is then developed to induce active patient participation during training tasks. The proposed control strategy divides the 3D space around the rehabilitation training path into a human-dominated area and a robot-dominated area. It encodes the space around the training path and endows the corresponding normal and tangential force; the tangential component assists with movement along the target path, and the normal component pushes the patient's hand towards the target path using a real-time adjustable controller. Compared with a common force-field controller, the human–robot interaction in this strategy is easy and can be quickly adjusted by changing the force field's range or the variation characteristics of two forces, and the intervention in two directions can change continuously and smoothly despite the patient's hand crossing the two areas. Visual guidance based on the Unity-3D environment is introduced to provide visual training instructions. Finally, the feasibility of the proposed control scheme is validated via training experiments using five healthy subjects.
Zero-dimensional study of the compression of low-temperature spheromaks

Compression of low-temperature spheromak plasmas has been studied with the aid of a zero-dimensional two-fluid computer code. The major direct effect of compression is to raise the current and plasma densities, keeping their ratios constant. Above critical pre-compression values of the electron temperature, Te, and the product of electron density and particle confinement time, neτp, the rising plasma density shifts the impurity ions to higher ionization states, with correspondingly lower radiative losses. High post-compression temperatures may thus be achieved. In oxygen radiation-dominated plasmas with pre-compression values above the critical ones, and with constant τp, the electron temperature can be increased by up to a factor of seven for a compression of a factor of two. This can be compared with a factor-of-four temperature rise expected for adiabatic compression. If the energy balance is dominated by particle confinement losses rather than radiation losses, the effect of compression is to raise the temperature as Te ∼ C6/5, for constant τp.
Magnetic excitations and phonons in the spin-chain compound NaCu2O2

We report an inelastic light scattering study of single-crystalline $\mathrm{Na}{\mathrm{Cu}}_{2}{\mathrm{O}}_{2}$, a spin-chain compound known to exhibit a phase with helical magnetic order at low temperatures. Phonon excitations were studied as a function of temperature and light polarization, and the phonon frequencies are compared to the results of ab initio lattice dynamical calculations, which are also reported here. The good agreement between the observed and calculated modes allows an assignment of the phonon eigenvectors. Two distinct high-energy two-magnon features as well as a sharp low-energy one-magnon peak were also observed. These features are discussed in terms of the magnon modes expected in a helically ordered state. At high temperatures, the spectral features attributable to magnetic excitations are replaced by a broad, quasielastic mode due to overdamped spin excitations.
A 300 nW 10 kHz Relaxation Oscillator with 105 ppm/ ◦ C Temperature Coefﬁcient

An on-chip nanopower RC relaxation oscillator is developed in a 180-nm standard CMOS process, consuming 300 nW while running at 10 kHz. Employing a frequency compensation scheme that reduces the frequency drift introduced by comparator offset and delay, the proposed oscillator achieves a signiﬁcant low temperature coefﬁcient. Furthermore, a supply regulation structure is used to reduce the frequency sensitivity to supply voltage variations. Post-simulation results show that the frequency variation against temperature is 105 ppm/ ◦ C in the temperature range from 0 to 85 ◦ C, and the line sensitivity is 2.19%/V with the supply voltage changing from 1.05 to 1.45 V. At offset frequencies of 100 Hz and 1 kHz, the simulated phase noises are − 50 and − 71 dBc/Hz, respectively.
Extended Robust H 2 and H ∞ Filter Design for Discrete Time-Invariant Linear Systems with Polytopic Uncertainty

This paper is concerned with the problem of robust H 2 and H ∞ ﬁlter design for discrete-time linear time-invariant systems with polytopic parameter uncertainties. Less conservative robust H 2 and H ∞ ﬁlter design procedures are proposed in terms of single-parameter minimization problems with linear matrix inequality constraints. To this end, we generalize the ﬁlter structures available in the literature to date in such a way that the ﬁlter’s next state is built by summing the ﬁlter’s states over several samples from the past to the present. For stability of the ﬁltering error system, the homogeneous polynomial parameter-dependent Lyapunov functions are employed. Finally, illustrative examples are given to demonstrate the merits of the proposed methods.
High-Energy Emission from the Prompt Gamma-Ray Burst

We study the synchrotron and synchrotron self-Compton (SSC) emission from internal shocks that are responsible for the prompt gamma-ray emission in gamma-ray bursts (GRBs) and consider the relation between these two components, taking into account the high-energy cutoff due to pair production and Thomson scattering. We find that in order for the peak energy of the synchrotron to be Ep ~ 300 keV with a variability time tv ≳ 1 ms, a Lorentz factor of Γ ≲ 200 is needed, implying no high-energy emission above ~30 MeV and the synchrotron component dominating at all energies. If we want both Ep ~ 300 keV and prompt high-energy emission up to ~2 GeV, as detected by EGRET for GRB 940217, we need Γ ~ 600 and tv ~ 0.1 ms, which might be resolved by Super Agile. If such prompt high-energy emission is common in GRBs, as may be tested by the Gamma-Ray Large Area Space Telescope (GLAST), then for tv ≳ 1 ms, we need Γ ≳ 350, which implies Ep ≲ 100 keV. Therefore, if X-ray flashes are GRBs with high values of tv and Γ, they should produce ≳1 GeV emission. For an electron power-law index p > 2, the SSC component dominates the emission above ~100 MeV. Future observations by GLAST may help determine the value of p and whether the high-energy emission is consistent with a single power law (implying that one component, the synchrotron, is dominant) or has a break where the νFν slope turns from negative to positive, which implies that the SSC component becomes dominant above ~100 MeV. The high-energy emission is expected to show similar variability and time structure to that of the soft gamma-ray emission. Finally, we find that in order to see delayed high-energy emission from the prompt GRB due to pair production with the cosmic IR background, extremely small intergalactic magnetic fields (≲10-22 G) are required.
A Sub-100 ppm / ◦ C Temperature-Compensated High-Frequency CMOS Relaxation Oscillator

A temperature-compensated high-frequency CMOS integrated relaxation oscillator with low frequency variations is presented. A current-controlled oscillator topology is employed with a resistive source-degenerated transconductor and a current comparator to achieve high oscillation frequency and low power dissipation. The proposed oscillator was designed with process parameters from a standard 0.35- µ m CMOS technology and a 2.5-V single power supply voltage. At a nominal oscillation frequency of 21 MHz, the total power dissipation of the circuit was 201 µ W. Post-layout simulation results showed that the frequency variations were less than 34 . 16 ppm / ◦ C over a temperature range of − 40 to + 120 ◦ C.
An 8-bit, 10 KS/s, 1 . 87 µ W Successive Approximation Analog to Digital Converter in 0 . 25 µ m CMOS Technology for ECG Detection Systems

This paper presents an 8-bit successive approximation analog to digital converter (SA-ADC) employing a mostly digital implementation for portable Electrocardiogram (ECG) detection systems. At 10K samples/s, the proposed SA-ADC consumes 1 . 87 μ W from a 1V power supply. The layout and extraction of the proposed SA-ADC are done using L-edit and simulated using TSMC 0 . 25 μ m technology ﬁle on Pspice. According to the simulation results, the SA-ADC has a signal-to-noise ratio of 57 dB, peak spurious-free dynamic range of 41dB, and a signal-to-noise-and-distortion ratio of 40.5dB for a 200Hz–500mV pp input sine wave. In addition to that, the SA-ADC has effective number of bits of 6.5-bits, an effective resolution bandwidth of 1.5kHz and a ﬁgure of merit of 6.85pJ/Conversion step. The digitized ECG signal is precisely reconstructed using a novel reconstruction circuit. These results show that the proposed SA-ADC in 0 . 25 μ m technology is a good candidate for ECG detection systems.
Geometric constraint of mechanosensing in bone marrow stromal cell cultures prevents stiffness-induced differentiation

Extracellular matrix (ECM) stiffness is fundamental in cell division, movement and differentiation. The stiffness that cells sense is determined not only by the elastic modulus of the ECM material, but also by ECM geometry and cell density. We hypothesised that these factors would influence cell-traction-induced matrix deformations and cellular differentiation in bone marrow stromal cells (BMSCs). To achieve this, we cultivated BMSCs on polyacrylamide hydrogels that varied in elastic modulus and geometry and measured cell spreading, cell-imparted matrix-deformations and differentiation. At low cell density BMSCs spread to a greater extent on stiff compared to soft hydrogels, or on thin compared to thick hydrogels. Cell-imparted matrix deformations were greater on soft compared to stiff hydrogels or thick compared to thin hydrogels. There were no significant differences in osteogenic differentiation relative to hydrogel elastic modulus and thickness. However, increased cell density and/or prolonged culture significantly reduced matrix deformations on soft hydrogels to levels similar to those on stiff substrates. This suggests that at high cell densities cell traction-induced matrix displacements are reduced by both neighbouring cells and the constraint imposed by an underlying stiff support. This may explain observations of the lack of difference in osteogenic differentiation as a function of stiffness.