Threshold For Generation Research Articles

Performance investigation of high-efficiency widely tunable subnanosecond optical parametric generator and amplifier based on MgO:PPLN.

We report on experimental and theoretical studies of widely tunable high-efficiency subnanosecond optical parametric generator (OPG) and amplifier (OPA) based on a 2 cm long multigrating MgO-doped periodically-poled lithium niobate (MgO:PPLN) crystal pumped by a passively Q-switched Nd:YAG micro-laser. Our OPG can be continuously tuned from 1442 nm to 4040 nm with signal wave energies ranging from 33 μJ to 265 μJ and total OPG conversion efficiency up to 46 % that depended on the pump focusing conditions. Characterization of spatial properties of the OPG determine Lorentzian spatial profile of the signal beam with M 2≈2 that was also dependent on the pump focusing conditions. High OPG gain and subsequent pump depletion led to the adjustment of the output signal pulse duration in the range of 242 - 405 ps by varying the incident pump power. By using a distributed feedback (DFB) continuous-wave (CW) 1550 nm wavelength seed laser for the OPA operation we reduced the generation threshold up to 1.6 times, increased maximum conversion efficiency by 4 - 20%, and achieved nearly transform-limited output signal pulses. Experimentally measured characteristics were supplemented by numerical simulations based on the quantum mechanical model for the OPG, and classical three-wave interaction model for the OPA operation.

Optimisation of Buyer and Seller Preferences for Peer-to-Peer Energy Trading in a Microgrid

In this paper, an optimisation approach to prioritise buyers and sellers in a peer-to-peer (P2P) energy trading market based on distances from the aggregator has been developed. The proposed approach assigns higher preferences to buyers/sellers with a smaller distance, as this will allow lower losses in the power transmission. Under this approach, the sellers and buyers operate in a decentralised manner to optimise the preference coefficients along with the energy sold/purchased to achieve certain profits/savings. The proposed approach is implemented using a real-life dataset, and the impacts of different parameters, such as seasonal variations in renewable generation, distances and profit thresholds for sellers, have been investigated. The results show that the proposed approach allows buyers and sellers to purchase/sell more energy from the P2P trading market (2.4 times increase when maximum energy sold is considered) in comparison to the case when all participants are equally preferred. It has been observed that, with increasing distances, sellers are assigned a smaller preference coefficient, which results in sellers being willing to sell a higher amount of energy so that they can achieve the same profit threshold.

Chipping Energy Threshold in MEMS Sensors

This research faces the problem of identifying the impact energy for which silicon chips are generated after shocks in microdevices, with the aim of providing design guidelines for next generation robust inertial sensors. The issue is tackled through the design of an on-chip test structure capable of generating up to 100 nJ of impact energy onto a stopping bump, corresponding to 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> -10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> gravity units of acceleration for a wide range of state-of-the art gyroscopes and accelerometers. The additional challenge of identifying the presence of debris without the need to uncap the dice is faced through the design of interdigitated electrodes underneath the impact area, and the measurement of small leakage currents caused by debris-induced short circuits between them. Statistical tests performed on 27 samples of different bump shape not only enable to identify an energy threshold for debris generation at about 10 nJ, valid at least for the considered process, but also suggest how the bump shape significantly influences this phenomenon. [2021-0257]

Hyperhomocysteinemia Increases Cortical Excitability and Aggravates Mechanical Hyperalgesia and Anxiety in a Nitroglycerine-Induced Migraine Model in Rats.

Homocysteine is a sulfur-containing endogenous amino acid leading to neurotoxic effects at high concentrations. Population studies suggest an association between plasma homocysteine levels and the risk of migraine headaches. The aim of this study was to analyze the sensitivity of rats with prenatal hyperhomocysteinemia (hHCY) in respect of the development of behavioral correlates of headache and spreading cortical depolarization (CSD) in a migraine model induced by the administration of the nitric oxide (NO) donor nitroglycerin. Animals with hHCY were characterized by migraine-related symptoms such as mechanical hyperalgesia, high-level anxiety, photophobia, as well as an enhanced level of neuronal activity in the somatosensory cortex along with a lower threshold of CSD generation. Likewise, acute or chronic intermittent administration of nitroglycerin also induced the development of mechanical allodynia, photophobia and anxiety in control groups. However, these symptoms were more pronounced in rats with hHCY. Unlike hHCY, nitroglycerin administration did not affect the threshold of CSD generation, but like hHCY, increased the background neuronal activity in layers 2/3 and 4 of the cerebral cortex. The latter was more pronounced in animals with hHCY. Thus, the migraine profile associated with hHCY can be further exaggerated in conditions with enhanced levels of migraine triggering the gaseous transmitter NO. Our data are consistent with the view that high levels of plasma homocysteine can act as a risk factor for the development of migraine.

Evaluation method of hydrocarbon yield of source rocks in open, semiopen, and closed systems: A case study on the K1qn Formation, northern Songliao Basin, China

Hydrocarbon yield of source rocks is an important parameter in the evaluation of oil and gas resources, and its value determines the potential of conventional and unconventional oil and gas resources. There is no oil cracking into gas in the thermal pyrolysis experiment data of an open system, whereas kerogen cracking into oil in a closed system is involved in the calculation of oil cracking into gas. However, most source rocks in sedimentary basins are a process of hydrocarbon generation and hydrocarbon expulsion, which could lead to insufficient understanding of hydrocarbon yield of source rocks. Based on the multiple thermal pyrolysis experiment data, three hydrocarbon generation kinetic models, and actual geologic data (burial history, thermal history, and hydrocarbon generation threshold), we established the evaluation method and chart of hydrocarbon yield of source rocks under open, semiopen, and closed systems by using the hydrocarbon generation kinetics method. The concept of degree of openness was proposed. From a closed system to an open system, the degree of openness increases gradually, and its value changes from 0 to 1. Taking the K1qn Formation in the northern Songliao Basin as an example, the hydrocarbon expulsion efficiency of the K1qn Formation source rock is approximately 70%, and it can be approximated as the degree of openness. Based on our method for evaluating hydrocarbon yield of source rocks, the charts of hydrocarbon yield of source rocks under open system, semiopen system with a degree of openness of 0.7, and closed system of the K1qn Formation in the northern Songliao Basin were established. The oil and gas yields of the K1qn Formation source rocks in a semiopen system with a degree of openness of 0.7 are approximately 540 and 105 mgHC/gTOC at a burial depth of 2000 m, respectively. Our results indicate that the hydrocarbon yield of source rocks in a semiopen system is closer to the hydrocarbon yield of source rocks under geologic condition. We use the thermal pyrolysis experiment data, hydrocarbon generation kinetics model, and geologic data to propose a very valuable evaluation method of hydrocarbon yield of source rock, which has a solid theoretical basis and strong applicability.

Superradiance of Spin Defects in Silicon Carbide for Maser Applications

Masers as telecommunication amplifiers have been known for decades, yet their application is strongly limited due to extreme operating conditions requiring vacuum techniques and cryogenic temperatures. Recently, a new generation of masers has been invented based on optically pumped spin states in pentacene and diamond. In this study, we pave the way for masers based on spin S = 3/2 silicon vacancy (VSi) defects in silicon carbide (SiC) to overcome the microwave generation threshold and discuss the advantages of this highly developed spin hosting material. To achieve population inversion, we optically pump the VSi into their mS = ±1/2 spin sub-states and additionally tune the Zeeman energy splitting by applying an external magnetic field. In this way, the prerequisites for stimulated emission by means of resonant microwaves in the 10 GHz range are fulfilled. On the way to realising a maser, we were able to systematically solve a series of subtasks that improved the underlying relevant physical parameters of the SiC samples. Among others, we investigated the pump efficiency as a function of the optical excitation wavelength and the angle between the magnetic field and the defect symmetry axis in order to boost the population inversion factor, a key figure of merit for the targeted microwave oscillator. Furthermore, we developed a high-Q sapphire microwave resonator (Q ≈ 104–105) with which we find superradiant stimulated microwave emission. In summary, SiC with optimized spin defect density and thus spin relaxation rates is well on its way of becoming a suitable maser gain material with wide-ranging applications.

Spatial Dispersion in Hypercrystal Distributed Feedback Lasing.

This work is a first approach to investigate the role of spatial dispersion in photonic hypercrystals (PHCs). The scope of the presented analysis is focused on exploiting nonlocality, which can be controlled by appropriate design of the structure, to obtain new light generation effects in a distributed feedback (DFB) laser based on PHC, which are not observable under weak spatial dispersion. Here, we use effective medium approximation and our original model of threshold laser generation based on anisotropic transfer matrix method. To unequivocally identify nonlocal generation phenomena, the scope of our analysis includes comparison between local and nonlocal threshold generation spectra, which may be obtained for different geometries of PHC structure. In particular, we have presented that, in the presence of strong spatial dispersion, it is possible to obtain spectrally shifted Bragg wavelengths of TE- and TM-polarization spectra, lowered generation threshold levels for both light polarizations, generation of light of selected light polarization (TE or TM), or simultaneous generation of TE- and TM-polarized waves at different frequencies with controllable spectral separation, instead of single mode operation anticipated with local approach.

Differences and origins of hydrocarbon generation characteristics between mudstone and shale in the Seventh Member of the Yanchang Formation, Ordos Basin, China

Organic-rich black shale and dark-grey mudstone are widespread in the Seventh Member of the Yanchang Formation, Ordos Basin. There are obviously differences in geochemical characteristics and hydrocarbon generation potential between black shale and dark-grey mudstone. Based on the detailed organic geochemical examination, this paper reveals the differences in hydrocarbon generation processes and characteristics (activation energy and conversion rate of hydrocarbon generation) between dark-grey mudstone and black shale and the causes for the differences. Black shale is characterized by moderate to very high total organic carbon (TOC) contents (5.08%–39.39%) and its kerogen type belongs to type II1 and type I. Dark-grey mudstone has a characteristic of low to moderate TOC contents (0.64%–7.35%) and its kerogen types are mainly composed of type II2 and type II1. The hydrocarbon generation activation energy of black shale mainly oscillates around 250–310 KJ/mol, and the corresponding hydrocarbon generation threshold is high (the simulated temperature is 400 °C). The process of hydrocarbon generation is characterized by fast conversion rate and short cycle. By contrast, the hydrocarbon generation activation energy of dark-grey mudstone has a wide range (170–360 KJ/mol), and the corresponding hydrocarbon generation threshold is low (the simulated temperature is 230 °C). The process of hydrocarbon generation is characterized by slow conversion rate and long cycle. The difference of hydrocarbon generation process and characteristics between black shale and dark-grey mudstone is mainly affected by macerals composition and organic matter source. The organic matter of black shale mainly originated from algae, and its macerals was mainly composed of alginite. The organic matter of dark-grey mudstone mainly originated from the mixture of algae and terrestrial higher plants (conifers), and its macerals was mainly composed of vitrinite, liptodetrinite and inertinite. The complex macerals composition and organic matter source make the activation energy distribution of dark-grey mudstone more dispersed than that of black shale. In addition, affected by the macerals (e.g sporinite and resinite) with low activation energy from terrestrial higher plants, the activation energy of dark-grey mudstone containing sporinite and resinite in the macerals is lower than black shale. Therefore, the dark-grey mudstone containing algae and terrestrial higher plants corresponds to low hydrocarbon generation threshold, slow conversion rate and long hydrocarbon generation cycle. The black shale containing a large number of algae corresponds to high hydrocarbon generation threshold, fast conversion rate and short hydrocarbon generation cycle. Moreover, the conversion rate of black shale containing radioactive elements and more clay minerals is higher than that of dark-grey mudstone.

Study on Pore Structure and Fractal Characterization during Thermal Evolution of Oil Shale Experiments.

In order to better study the characteristics of the pore structure and to explore the influence factors of its fractal dimensions during the thermal evolution of oil shale, the immature oil shale (Tmax = 433 °C, TOC = 28.00%) of the Ordos Basin Extension Group was selected to simulate the whole thermal evolution process from immature to over mature in a semiopen system. Organic geochemical data show that the thermal simulation hydrocarbon generation threshold is between 300 and 400 °C. According to AIP-SEM observation, the pore types of the samples are different in different thermal simulation stages. The fractal dimensions are calculated by low-temperature N2 adsorption data using the fractal Frenkel–Halsey–Hill fractal model. The average surface fractal dimension (D1) is 2.26, indicating that the pore (<4 nm) surface is relatively smooth. The average pore structure fractal dimension (D2) is 2.49, indicating that the pore (>4 nm) structure is complex. Through the exploration of the relationship between fractal dimensions and organic geochemistry, whole rock X-ray diffraction, and N2 adsorption data, it is found that fractal dimensions have different degrees of correlation with thermal maturity, mineral composition, TOC content, and pore parameters. Through comprehensive research, it shows that hydrocarbon generation and expulsion, oil and gas cracking, and organic matter carbonization have important effects on the pore structure and fractal characteristics of oil shale.

Enhancement of multi-filament generation and filament-induced fluorescence by turbulence

Exploring the influence of atmospheric turbulence on remote sensing based on filament-induced fluorescence is still challenging. In this study, we applied artificial turbulence during remote filamentation and recorded the enhanced backward fluorescence of nitrogen. At the strongest turbulence, the nitrogen fluorescence signal was higher than that obtained when no turbulence was applied. The air turbulence introduces random noise in the laser profile, which is subsequently amplified by self-focusing effect and causes multiple filamentation. Moreover, by lowering the threshold for multiple filaments generation, turbulence led to an increase in the number of filaments, thereby enhancing fluorescence.

Second harmonic generation, photoluminescence and laser damage threshold of L–Proline strontium chloride monohydrate: a prospective NLO tunable band gap for optoelectronic applications

Second harmonic generation, photoluminescence and laser damage threshold of L–Proline strontium chloride monohydrate: a prospective NLO tunable band gap for optoelectronic applications

The effect of pump beam focusing characteristics on stimulated Brillouin scattering

Parameters including pump energy, beam waist radius, length of gain medium and beam divergence all affect the generation threshold and output pulse characteristics of lasers that utilize the stimulated Brillouin scattering (SBS) effect. In this paper, we investigate the effect that changes to the pump beam focusing parameters (namely beam divergence and beam waist) have on the output characteristics of the Stokes beam generated through the SBS process. This study is conducted both theoretically and experimentally using a single-cell SBS structure. The results highlight that pump beams with a small divergence angle at the focal point within the SBS cell are favorable for the generation of Stokes beams with short pulse lengths. Here, we demonstrate the generation of a Stokes beam with a pulse width of 854 ps using a pump pulse with a pulse width of 7.2 ns, which was focused to a spot with a divergence angle of 2.48 mrad.

Chaotic dynamics on exceptional surfaces

Due to strong photon-phonon interaction, coupled microcavities have provided a fruitful platform for chaos investigation. In particular, the parity-time symmetric microcavities pair has attracted unprecedented attention since the exceptional point (EP) in the non-Hermitian system offers more intriguing and abundant dynamics. Motivated by achieving a robust EP, a novel exceptional surface (ES) notion is proposed in the coupled microcavities. However, the chaotic dynamics on the ES remain yet unexplored. This study explores the chaos generation on the ES. We discover that the ES could dramatically decrease the threshold of chaos generation by &gt;50% compared to the eigenvalues escaping from the ES. Unlike conventional chaotic dynamics, chaotic signals on the ES possess a surprising globally flattened, but locally chirped spectrum. Such an advantage provides an additional degree of freedom to implement chaotic applications on the physical layer. In addition, a coupling phase-induced chaos is found, which demonstrates an accumulated chaos generation beyond the conventional wisdom. More importantly, such an arrangement enables chaotic signals to achieve the temporal Vernier and harmonic Vernier effects, expanding the scope of chaos. This study of chaos generation on the ES further stimulates applications in compact chaotic devices and potentially facilitates fundamental chaotic dynamics research.

Afterhyperpolarization Promotes the Firing of Mitral Cells through a Voltage-Dependent Modification of Action Potential Threshold.

In the olfactory bulb, mitral cells (MCs) display a spontaneous firing that is characterized by bursts of action potentials (APs) intermixed with silent periods. Intraburst firing frequency and duration are heterogeneous among MCs and increase with membrane depolarization. By using patch-clamp recording on rat slices, we dissected out the intrinsic properties responsible for this bursting activity. We showed that the threshold of AP generation dynamically changes as a function of the preceding trajectory of the membrane potential. In fact, the AP threshold became more negative when the membrane was hyperpolarized and had a recovery rate inversely proportional to the membrane repolarization rate. Such variations appeared to be produced by changes in the inactivation state of voltage-dependent Na+ channels. Thus, AP initiation was favored by hyperpolarizing events, such as negative membrane oscillations or inhibitory synaptic input. After the first AP, the following fast afterhyperpolarization (AHP) brought the threshold to more negative values and then promoted the emission of the following AP. This phenomenon was repeated for each AP of the burst making the fast AHP a regenerative mechanism that sustained the firing, AHP with larger amplitudes and faster repolarizations being associated with larger and higher-frequency bursts. Burst termination was found to be because of the development of a slow repolarization component of the AHP (slow AHP). Overall, the AHP characteristics appeared as a major determinant of the bursting properties.

Source rock evaluation within a sequence stratigraphic framework of the Palaeogene Liushagang Formation in the Fushan Depression, South China Sea

The Fushan Depression is one of the prolific hydrocarbon‐bearing depressions in the Beibuwan Basin, South China Sea. In this study, a total of 133 mudstone samples, 18 well‐logging curves, and 12 seismic sections were analysed to investigate the geochemical features and spatial distribution of effective source rocks of the Palaeogene Liushagang Formation within a sequence stratigraphic geochemical framework. The results suggest that depositional centres of mudstones northward migrated from the central Huangtong Sag during the Liushagang period. Good hydrocarbon generation potential source rocks containing Type II kerogen occur in the transgressive systems tract (TST)–highstand systems tract (HST) of lower Liushagang sequence (SQls3), the middle Liushagang sequence (SQls2), and the lowstand systems tract (LST)–TST of upper Liushagang sequence (SQls1). The occurrence of effective source rock kitchens, which are mainly controlled by the thermal maturity is distributed in the strip‐shaped area of SQls3 sequence, the whole Huangtong Sag of SQls2 sequence, and the central and northern part of Huangtong Sag of SQls1 sequence, respectively. Fewer hydrocarbon accumulations were found in the southern slope due to the relatively deeper hydrocarbon generation threshold depth and to the limited occurrence of effective source rock kitchens.

Assessment of Inter-Laboratory Differences in SARS-CoV-2 Consensus Genome Assemblies between Public Health Laboratories in Australia.

Whole-genome sequencing of viral isolates is critical for informing transmission patterns and for the ongoing evolution of pathogens, especially during a pandemic. However, when genomes have low variability in the early stages of a pandemic, the impact of technical and/or sequencing errors increases. We quantitatively assessed inter-laboratory differences in consensus genome assemblies of 72 matched SARS-CoV-2-positive specimens sequenced at different laboratories in Sydney, Australia. Raw sequence data were assembled using two different bioinformatics pipelines in parallel, and resulting consensus genomes were compared to detect laboratory-specific differences. Matched genome sequences were predominantly concordant, with a median pairwise identity of 99.997%. Identified differences were predominantly driven by ambiguous site content. Ignoring these produced differences in only 2.3% (5/216) of pairwise comparisons, each differing by a single nucleotide. Matched samples were assigned the same Pango lineage in 98.2% (212/216) of pairwise comparisons, and were mostly assigned to the same phylogenetic clade. However, epidemiological inference based only on single nucleotide variant distances may lead to significant differences in the number of defined clusters if variant allele frequency thresholds for consensus genome generation differ between laboratories. These results underscore the need for a unified, best-practices approach to bioinformatics between laboratories working on a common outbreak problem.

First principles investigations of the structural, electronic, mechanical, linear and nonlinear optical properties of RbIO2F2

Rubidium fluoroiodate has been reported to be a potential mid-infrared nonlinear optical material, due to its second harmonic generation (SHG) and Laser damage threshold value of 156 MW/cm2. In this study, the linear and nonlinear optical properties are investigated and analyzed using the density functional theory by full potential linearized augmented plane wave (FP-LAPW) and plane wave pseudo-potential (PP-PW). The FP-LAPW method is used to study the electronic properties and linear optical properties with the recently developed density functional of Tran and Blaha. Furthermore, optical features such as dielectric functions, absorption coefficient, refractive index, reflectivity, electron energy loss function are calculated for photon energies up to 40 eV. The elasticity, SHG response, linear electro-optical effect, and piezoelectricity are studied by the PP-PW approximation. Based on the semi-empirical relations, the Young's modulus, shear and bulk modulus, Poisson's ratio, anisotropic factors, sound velocities, Debye temperature, and hardness have been determined.

Integrated hydrological, power system and economic modelling of climate impacts on electricity demand and cost

Impacts of climate-related water stress and temperature changes can cascade through energy systems, although models have yet to capture this compounding of effects. Here, we employ a coupled water–power–economy model to capture these important interactions in a study of the exceedance of water temperature thresholds for power generation in the western United States. We find that not all reductions in reserve electricity-generation capacity result in impacts, and that when they occur, intermittent interruptions in electricity supply at critical times of the day, week and year account for much of the economic impacts. Finally, we find that impacts may be in different locations from the original water stress. We estimate that the consumption loss can be up to 0.3% annually and the drivers identified in coupled modelling can increase the average cost of electricity by up to 3%.

Особенности усиления флуоресценции в насыщенных флуорофорами полимерных пенах

The results of experimental studies of the fluorescence response of polylactide foams saturated with rhodamine 6G and composites used for their preparation in the region of transition from spontaneous fluorescence to stochastic laser generation are presented. A small increase in the threshold of stochastic laser generation in foamed composites compared to the expected one is interpreted as a result of the contribution of the waveguide mode of fluorescence propagation in the polymer matrix.

Features of fluorescence enhancement in fluorophore-saturated polymer foams

The results of experimental studies of the fluorescence response of polylactide foams saturated with rhodamine 6G and composites used for their preparation in the region of transition from spontaneous fluorescence to stochastic laser generation are presented. A small increase in the threshold of stochastic laser generation in foamed composites compared to the expected one is interpreted as a result of the contribution of the waveguide mode of fluorescence propagation in the polymer matrix.. Keywords: polylactide foam, spontaneous fluorescence, stochastic laser generation, waveguide mode.