物理最新文献

In this work, we holographically study the hydrodynamical properties of (mathcal {N} = 4) strongly coupled Super Yang–Mills baryon rich thermal plasma with large number of flavour quarks. Specifically, we study the drag force acting on the moving heavy probe quark and corresponding energy loss. We also study the jet quenching parameter, screening length and binding energy of the quark–antiquark pair. Due to the presence of finite baryon density and flavour quarks the drag force, energy loss, jet quenching parameter and binding energy of the quark–antiquark pair are enhanced for the increase in temperature. However, the screening length of the quark–antiquark pair is reduced, leading to the thermal plasma phase being achieved at a lower temperature, which is consistent with the thermal phase diagram of the quark–gluon plasma. We observed that the perpendicular orientation of quark–antiquark pair with respect to the direction of motion deconfined early compare to the parallel orientation once temperature raises.

Lifetimes of excited states of positive and negative parity (Delta )I = 2 bands of (^{106})Cd have been measured using the Doppler Shift Attenuation Method (DSAM). The electric quadrupole reduced transition probability rates, B(E2), show a significant decreasing trend with increasing spin along with large observed (Im ^{(2)})/B(E2) values. The experimental observations, interpreted in the framework of semiclassical particle-rotor model (SCM) calculations, suggest that these bands have the character of twin-shears type anti-magnetic rotational bands resulting from the coupling of g(_{9/2}) proton holes with h(_{11/2}), g(_{9/2}) and d(_{5/2}) neutron particles. Another negative-parity band in the same nucleus has been studied using SCM, which also interprets it to be an anti-magnetic rotational band.

We consider gravitationally induced corrections to inflaton potentials driven by supersymmetry breaking in a five-dimensional supergravity, compactified on a ( S_1/Z_2 ) orbifold. The supersymmetry breaking takes place on the hidden brane and is transmitted to the visible brane through finite one loop graphs giving rise to an inflaton potential which includes gravitationally induced terms. These corrections are significant for inflationary cosmology and have the potential to modify the predictions of widely studied supergravity models if the latter are embedded in this framework. To explore these effects we examine two classes of models those inspired by no-scale supergravity models and (alpha )-attractors. Both models are compatible with current cosmological observations but face chalenges in reconciling enhanced values for the scalar power spectrum ( P_zeta ) with cosmological data, particularly regarding the tensor to scalar ratio r. In fact ( P_zeta gtrsim 10^{-2}) results to ( r > {mathcal {O}} (0.1) ), outside the limits put by current data.

We review the developmental activities in the field of radiation detectors and coupled instrumentation/electronics at IUAC (formerly NSC). The facility focuses on nuclear reaction and structure studies around the Coulomb barrier using ion beams from the accelerator. To execute these experiments, IUAC has a detector development program for preparing detector systems based on position sensitive fast timing proportional/avalanche counters, particle identification detectors such as segmented ionization chambers, hybrid gas-silicon telescopes, segmented and resistive position sensitive silicon detectors, and scintillators for light-charged particle, neutron and γ-ray detection, and germanium detectors for high resolution γ-ray spectroscopy. This is further exalted by a strong front-end electronics development program for detector signal processing. Different types of stand-alone and multi-channel low noise preamplifiers (charge sensitive and fast timing), spectroscopy amplifiers, discriminators, logic units, etc. have been developed. Customized high resolution analog to digital converters, trigger generator cum event identifier module for handling trigger signals for multi-detector arrays, crate controllers, synchronizing and time stamping units have been developed in CAMAC as well as VME standards for the data acquisition system. This nuclear instrumentation has been routinely used to perform experiments of fusion and fusion-fission dynamics, and nuclear spectroscopy using the facilities of recoil mass spectrometers, scattering chamber, neutron and gamma detector arrays etc. New detector systems are being planned and developed for these facilities as well as for the future international facilities such as NUSTAR. This article describes an overview of detector instrumentation activities.

The Higgs-portal scalar dark matter (DM) model is a simple extension of the Standard Model (SM) to incorporate a DM particle to the SM, where a (Z_2)-odd real scalar field is introduced as a DM candidate. We consider this DM model in the context of 5-dimensional brane-world cosmology, where our 3-dimensional space is realized as a hyper-surface embedded in 4-dimensional space. In the setup, all the SM and DM fields reside on the hyper-surface while graviton lives in the bulk. We consider two well-known brane-world cosmologies, namely, the Randall–Sundrum (RS) and the Gauss–Bonnet (GB) brane-world cosmologies, in which the standard Big Bang cosmology is reproduced at low temperatures below the so-called “transition temperature” while at high temperatures the expansion law of the universe is significantly modified. Such a non-standard expansion law directly impacts the prediction for the relic density of the Higgs-portal DM. We investigate the brane-world cosmological effects and identify the allowed model parameter region by combining the constraints from the observed DM relic density, and the direct and indirect DM detection experiments. It is well-known that only DM masses in the vicinity of half the Higgs boson mass are allowed in the Higgs-portal scalar DM model. We find that the allowed parameter region becomes more severely constrained and even disappears in the RS cosmology, while the GB cosmological effect significantly enlarges the allowed region. Upon discovering Higgs-portal DM, we can determine transition temperature in the GB brane-world cosmology.

In this work, we investigate the transition form factors for (Lambda _brightarrow {Lambda (1520)}) within the framework of light-cone sum rules (LCSR), using the light-cone distribution amplitudes (LCDAs) of the (Lambda _b)-baryon. In the hadronic representation of the correlation function, we carefully select the appropriate Lorentz structures and isolate the contributions from both the (Lambda (1520)(J^P=(3/2)^-)) and the (Lambda (1890)(J^P=(3/2)^+),) ensuring that the form factors for (Lambda _brightarrow {Lambda (1520)}) can be calculated unambiguously. We also provide predictions for various physical observables in the decay (Lambda _brightarrow {Lambda (1520)}l^+l^-,) including the differential branching fraction, the lepton-side forward–backward asymmetry, the longitudinal polarization fraction, and the CP-averaged normalized angular observable. Our prediction for the differential branching fraction of (Lambda _brightarrow {Lambda (1520)}mu ^+mu ^-) is in good agreement with the LHCb measurement within the uncertainties.

Silica aerogels have emerged as promising candidates as platforms for a variety of devices, including those used for magnetic logic and sensing. However, their non-planar structure also poses challenges for their use as substrates for thin film devices. For example, substrate disorder is established to strongly influence anisotropy in thin film magnetic materials. Here, we evaluate the substrate effect on induced uniaxial anisotropy in permalloy (Py) thin films and patterned structures, wherein the uniaxial anisotropy is clearly linked to a directionality of the magnetization hysteresis and modifications to zero field domain structures relative to a standard thermally oxidized Si substrate. The strength and direction of this anisotropy vary with location, indicating its non-uniform nature, and is estimated to be as large as 700 J/m³ for 25 nm thick permalloy films, and decreases with increasing Py thickness. This substrate induced anisotropy is strong enough to modify the domain structures present in patterned magnetic elements and can have significant implications for the development of magnetic devices on aerogel substrates. Results are compared and found to be consistent with micromagnetic modelling of expected domain structures.

In this manuscript, an approach for generation of flattened optical frequency comb (OFC) by using four wave mixing (FWM) effect in wideband Semiconductor optical amplifier (SOA) is proposed. The performance of proposed OFC has been analysed in presence of multi-tone RF modulated signal. The wideband SOA produces a comb-like spectrum comprised of numerous closely spaced frequency components by modulating the input light wave with a single frequency and interaction of these light waves inside the amplifier produced new frequency components. The proposed optical network is proficient for generating 58 comb lines with 2 dB maximum power deviation in which 28, 19 and 11 frequency comb lines having 2 dB maximum power deviation. The impact of confinement factor, injection current and carrier density of wideband SOA is investigated to get variations in optical frequency comb lines and maximum power deviation. This flattened OFC has advanced application in passive optical network as well as in optical sensing and it can act as multichannel source in high performance optical networks.

The temperature measurement of engine hot-end components is crucial for evaluating and monitoring the component’s lifetime. Luminescence thermometry demonstrates significant potential for engine testing applications. However, in engine combustion environments, the luminescence imaging thermometry of hot-end components wrapped in high-temperature, high-pressure, and high-speed combustion gas flow still faces challenges such as coating reliability and flame interference. Therefore, this paper conducted a study on the measurements of blade temperature distribution in engine combustion environments using two-color luminescence imaging thermometry based on atmospheric-plasma-sprayed YAG:Dy (Dysprosium-doped yttrium aluminum garnet) coating. YAG:Dy coatings were prepared on a metal substrate using APS (Atmospheric plasma spray) technology. By carrying out systematic emission spectroscopy experiments at varying temperatures (300–1273 K) and oxygen concentrations (0% (N₂) and 21% (air)), we comparatively investigated the temperature and oxygen concentration dependence of the luminescence intensity ratio (LIR) for both YAG:Dy coatings and powder samples. The experimental results revealed distinct thermometric performance characteristics between the two sample types. Notably, the dense APS YAG:Dy coating exhibited stable luminescence intensity and LIR values across varying oxygen concentrations, demonstrating its suitability for temperature measurement in environments with fluctuating oxygen concentrations, such as combustion and catalytic reactions. Then, the optimal measurement windows for luminescence intensity ratio measurements were determined through spectral analysis of jet fuel combustion flames. A two-color luminescence imaging thermometry system was established based on pulse excitation and detection coaxial optical path, single ICCD (Intensified charge-coupled device) coupled dual spectrum synchronous imaging. The calibration of the imaging thermometry system and the temperature calibration of the luminescence intensity ratio of APS YAG:Dy coating in the range of 573–1273 K were carried out. Experimental measurements of blade temperature distribution were performed under steady-state conditions in an engine combustor test rig (inlet total pressure ~ 2 atm, exhaust total temperature 1000–1170 K). The maximum measured temperature of the blade was about 1163.6 K, and the minimum relative standard deviation range of temperature was 0.30% ~ 0.48%. The reliability and thermometric performance of the APS YAG:Dy luminescent coating were validated under high-speed, high-temperature gas flow conditions, confirming the efficacy of the developed two-color luminescence imaging thermometry system. This research provides valuable insights for implementing luminescence imaging thermometry in engine combustion environments, particularly for dynamic targets and transient processes.