Non-thermal Energy Distribution Research Articles

Thermoelectricity without absorbing energy from the heat sources

We analyze the power output of a quantum dot machine coupled to two electronic reservoirs via thermoelectric contacts, and to two thermal reservoirs – one hot and one cold. This machine is a nanoscale analogue of a conventional thermocouple heat-engine, in which the active region being heated is unavoidably also exchanging heat with its cold environment. Heat exchange between the dot and the thermal reservoirs is treated as a capacitive coupling to electronic fluctuations in localized levels, modeled as two additional quantum dots. The resulting multiple-dot setup is described using a master equation approach. We observe an “exotic” power generation, which remains finite even when the heat absorbed from the thermal reservoirs is zero (in other words the heat coming from the hot reservoir all escapes into the cold environment). This effect can be understood in terms of a non-local effect in which the heat flow from heat source to the cold environment generates power via a mechanism which we refer to as Coulomb heat drag. It relies on the fact that there is no relaxation in the quantum dot system, so electrons within it have a non-thermal energy distribution. More poetically, one can say that we find a spatial separation of the first-law of thermodynamics (heat to work conversion) from the second-law of thermodynamics (generation of entropy). We present circumstances in which this non-thermal system can generate more power than any conventional macroscopic thermocouple (with local thermalization), even when the latter works with Carnot efficiency.

XMM-Newtonstudy of 30 Doradus C and a newly identified MCSNR J0536−6913 in the Large Magellanic Cloud

Aims: We present a study of the superbubble (SB) 30 Dor C and the newly identified MCSNR J0536-6913 in the LMC. Methods: All available XMM-Newton data (exposure times of 420 ks EPIC-pn, 556 ks EPIC-MOS1, 614 ks EPIC-MOS2) were used to characterise the thermal X-ray emission in the region. An analysis of the non-thermal X-rays is also presented and discussed in the context of emission mechanisms previously suggested in the literature. These data are supplemented by X-ray data from Chandra, optical data from the MCELS, and radio data from ATCA and MOST. Results: The brightest thermal emission was found to be associated with a new supernova remnant, MCSNR J0536-6913. X-ray spectral analysis of MCSNR J0536-6913 suggested an ejecta-dominated remnant with lines of O, Ne, Mg, and Si, and a total 0.3-10 keV luminosity of ~8E+34 erg/s. Based on derived ejecta abundance ratios, we determined the mass of the stellar progenitor to be either ~18 M_sun or as high as >40 M_sun, though the spectral fits were subject to assumptions (e.g., uniform temperature and well-mixed ejecta). The thermal emission from the SB exhibited enrichment by alpha-process elements, evidence for a recent core-collapse SNR interaction with the SB shell. We detected non-thermal X-ray emission throughout 30 Dor C, with the brightest regions being highly correlated with the H-alpha and radio shells. We created a non-thermal spectral energy distribution for the north-eastern shell of 30 Dor C which was best-fit with an exponentially cut-off synchrotron model. Conclusions: Thermal X-ray emission from 30 Dor C is very complex, consisting of a large scale SB emission at the eastern shell wall with the brightest emission due to MCSNR J0536-6913. The fact that the non-thermal spectral energy distribution of the SB shell was observed to roll-off is further evidence that the non-thermal X-rays from 30 Dor C are synchrotron in origin.

Effect of non-thermal product energy distributions on ketohydroperoxide decomposition kinetics

The decomposition of ketohydroperoxides (OQ′OOH) to two radicals is commonly predicted to be the key chain branching step in low-temperature combustion. The possibility of a direct decomposition of the OQ′OOH from its initially produced energy distribution is studied with a combination of master equation (ME) and direct trajectory simulations. The temperature and pressure dependent rate constants for the thermal decomposition of a ketohydroperoxide, HOOCH2CH2CHO, to four product channels were computed using RRKM/ME methods. Direct dynamics calculations were initiated from a transition state in the O2+QOOH reaction network to understand the fraction of energy in that transition state that is converted into the internal energy of the OQ′OOH. A novel approach to solving the master equation is used to determine the probability that a vibrationally hot OQ′OOH either will be stabilized to a thermal distribution or will react to form new products. Under most conditions, the majority of vibrationally excited OQ′OOH will be quenched into a thermal distribution. At higher internal energies and lower pressures, however, a significant fraction of the hot OQ′OOH will decompose rather than thermalize. Proper interpretation of low-pressure experiments may require inclusion of vibrationally hot intermediates, particularly if a chemical kinetic mechanism is optimized against the low-pressure data.

Quantum Efficiency of Cold Electron Bolometer Optical Response

In this paper, we present the measurements of optical response dependence on power load of a Cold Electron Bolometer integrated in a twin slot antenna. These measurements are also compared to the models of the bolometer limit and the photon counter limit. The responsivity of ${\hbox{0.22}}\ast {\hbox{10}} ^{9} ~{\hbox{V}}/{\hbox{W}}$ was measured at 0.22 pW radiation power from a black body at 3.5 K. According to our estimations, for optimized device the voltage responsivity at 100 mK electron temperature can approach ${S} _{v} =10 ^{10} ~{\hbox{V}}/{\hbox{W}}$ for power load below 0.1 pW and decreases down to ${\hbox{10}} ^{7} ~{\hbox{V}}/{\hbox{W}}$ at 300 mK for 5 pW signal power in a sample with absorber volume of ${\hbox{5}}\ast {\hbox{10}} ^{-20} ~{\hbox{m}} ^{3}$ . In the case of low bath temperatures and high applied RF power the changes of tunneling current, dynamic resistance and voltage response are explained by non-thermal energy distribution of excited electrons. Distribution of excited electrons in such system at lower temperatures can be of non-Fermi type, hot electrons with energies of the order of 1 K tunnel from normal metal absorber to superconductor instead of relaxing down to thermal energy ${kT} _{e}$ in absorber before tunneling. This effect can reduce quantum efficiency of the bolometer at 350 GHz from $\eta ={hf}/{kT} _{\rm ph} > 100$ in ideal case down to single electron per absorbed photon ( $\eta =1$ ) in the high power case. Methods of preserving high quantum efficiency are discussed.

Sensitivity of ICF ignition conditions to non-Maxwellian DT fusion reactivity

The hotspot ignition conditions in ICF are determined by considering the power balance between fusion energy deposition and energy loss terms. Uncertainty in any of these terms has potential to modify the ignition conditions, changing the optimum ignition capsule design. This paper considers the impact of changes to the DT fusion reaction rate due to non-thermal ion energy distributions. The DT fusion reactivity has been evaluated for a class of non-Maxwellian distributions representing a perturbation to the tail of a thermal distribution. The resulting reactivity has been used to determine hotspot ignition conditions as a function of the characteristic parameter of the modified distribution. The hotspot ignition conditions in ICF can be determined by considering the power balance between fusion alpha particle energy deposition, hydrodynamic work and energy loss via radiation and electron thermal conduction (1). The resulting conditions may be sensitive to uncertainties in any of the key plasma physics models or assumptions. This paper considers the impact of changes to the DT fusion reaction rate due to the presence of non-thermal ion energy distributions. The reactivity,� v� , for thermonuclear fusion reactions is conventionally derived by averaging cross- section data over a Maxwell-Boltzmann energy distribution. In many situations, such as when plasmas are strongly shocked or rapidly heated by energetic particles, reacting ions may be better characterised by a non-Maxwellian distribution. Since the self-relaxation time is longer for ions at higher energies (2), such effects typically produce an enhancement or depletion within the tail of the distribution. At temperatures where the reactivity is dominated by the contribution of particles in the tail, even small changes to the distribution may have a potentially significant impact on the fusion reaction rate. The DT fusion reactivity has been evaluated for a class of non-Maxwellian distributions, the q-Gaussian distribution (3), which represent a perturbation to the tail of a thermal distribution. The resulting reactivity has been used to calculate a revised ideal ignition temperature (4) and to determine hotspot ignition conditions as a function of the characteristic parameter of the distribution. This initial assessment does not consider in detail the physical development of non-Maxwellian distributions. If conditions are found to show significant sensitivity, then the generation of distributions may be explored in future work via kinetic simulation.

Numerical simulation of exciton dynamics in Cu2O at ultra-low temperatures within a potential trap

We have studied theoretically the relaxation behaviour of excitons in cuprous oxide (Cu2O) at ultra-low temperatures when excitons are confined within a potential trap by solving numerically the Boltzmann equation. As relaxation processes, we have included in this paper deformation potential phonon scattering, radiative and non-radiative decay and Auger decay. The relaxation kinetics has been analysed for temperatures in the range between 0.3 and 5 K. Under the action of deformation potential phonon scattering only, we find for temperatures above 0.5 K that the excitons reach local equilibrium with the lattice, i.e. that the effective local temperature is coming down to the bath temperature, while below 0.5 K a non-thermal energy distribution remains. Interestingly, for all temperatures the global spatial distribution of excitons does not reach the equilibrium distribution, but stays at a much higher effective temperature. If we include further a finite lifetime of the excitons and the two-particle Auger decay, we find that both the local and the global effective temperature do not come down to the bath temperature. In the first case we find that a Bose–Einstein condensation (BEC) occurs for all temperatures in the investigated range. Comparing our results with the thermal equilibrium case, we find that BEC occurs for a significantly higher number of excitons in the trap. This effect could be related to the higher global temperature, which requires an increased number of excitons within the trap to observe the BEC. In the case of Auger decay, we do not find a BEC at any temperature due to the local heating of the exciton gas.

Electron attachment to POCl3. III. Measurement and kinetic modeling of branching fractions

Electron attachment to POCl(3) was studied in the bath gas He over the pressure range 0.4-3.1 Torr and the temperature range 300-1210 K. Branching fractions of POCl(3)(-), POCl(2)(-), Cl(-), and Cl(2)(-) were measured. The results are analyzed by kinetic modeling, using electron attachment theory for the characterization of the nonthermal energy distribution of the excited POCl(3)(-∗) anions formed and chemical activation-type unimolecular rate theory for the subsequent competition between collisional stabilization of POCl(3)(-∗) and its dissociation to various dissociation products. Primary and secondary dissociations and∕or thermal dissociations of the anions are identified. The measured branching fractions are found to be consistent with the modeling results based on molecular parameters obtained from quantum-chemical calculations.

SPECTRAL EVOLUTION OF SUPERLUMINAL COMPONENTS IN PARSEC-SCALE JETS

We present numerical simulations of the spectral evolution and emission of radio components in relativistic jets. We compute jet models by means of a relativistic hydrodynamics code. We have developed an algorithm (SPEV) for the transport of a population of nonthermal electrons including radiative losses. For large values of the ratio of gas pressure to magnetic field energy density, αB ∼ 6 × 104, quiescent jet models show substantial spectral evolution, with observational consequences only above radio frequencies. Larger values of the magnetic field (αB ∼ 6 × 102), such that synchrotron losses are moderately important at radio frequencies, present a larger ratio of shocked-to-unshocked regions brightness than the models without radiative losses, despite the fact that they correspond to the same underlying hydrodynamic structure. We also show that jets with a positive photon spectral index result if the lower limit γmin of the nonthermal particle energy distribution is large enough. A temporary increase of the Lorentz factor at the jet inlet produces a traveling perturbation that appears in the synthetic maps as a superluminal component. We show that trailing components can be originated not only in pressure matched jets, but also in overpressured ones, where the existence of recollimation shocks does not allow for a direct identification of such features as Kelvin–Helmholtz modes, and its observational imprint depends on the observing frequency. If the magnetic field is large (αB ∼ 6 × 102), the spectral index in the rarefaction trailing the traveling perturbation does not change much with respect to the same model without any hydrodynamic perturbation. If the synchrotron losses are considered the spectral index displays a smaller value than in the corresponding region of the quiescent jet model.

Wave Excitation in Magnetically Confined Plasmas with an Anisotropic Velocity Distribution

In magnetically confined plasmas, fluctuations in the ion cyclotron range of frequency (ICRF) will be driven by the presence of non-thermal ion energy distributions. In a typical discharge in the GAMMA 10 tandem mirror, Alfvén-ion-cyclotron (AIC) modes are spontaneously excited due to strong temperature anisotropy. On the other hand, in fusion-oriented devices with a toroidal configuration, neutral beam (NB) injection is commonly used to create high performance plasmas. The resultant high-energy ions are trapped in local mirrors and will form velocity distributions with strong anisotropy. Especially in burning plasma experiments on JET and TFTR, fusion-product (FP) ions form non-thermal ion energy distributions in the bulk plasma and ion cyclotron emission (ICE) has been observed. The main purpose of this work is to study the relation between AIC-modes and ICEs in magnetically confined plasmas with non-thermal energy distributions. Recently, fluctuation measurements made by using ICRF antennas as pickup loops on JT-60U have been started. When the deuterium-NBs are injected into deuterium bulk plasma, magnetic fluctuations due to injected beams and FP ions are detected. Wave excitation near the ion cyclotron frequency and its higher harmonics is studied experimentally in plasmas with non-thermal ion energy distributions.

Laser-induced alkali atom desorption from thin sodium films on quartz prisms

Abstract The dynamics of visible ( λ =532 nm) and near-infrared ( λ =1064 nm) laser-induced desorption of alkali atoms from thin metal films deposited on quartz prisms is investigated. Upon desorption the atoms show non-thermal kinetic energy distributions with mean kinetic energies of 24, 150 and 350 meV at 532 nm and 14 meV at 1064 nm, independent of laser fluence. The thresholds for the appearance of these contributions are 0, 50 and 110 mJ/cm 2 , respectively. No threshold is observed for 1064 nm desorption. The results are discussed in terms of direct electronic versus multiphonon scattering assisted desorption.

Energy relaxation during hot-exciton transport in quantum wells: Direct observation by spatially resolved phonon-sideband spectroscopy

We investigate the energy relaxation of excitons during the real-space transport in ZnSe quantum wells by using microphotoluminescence with spatial resolution enhanced by a solid immersion lens. The spatial evolution of the LO-phonon sideband, originating from the LO-phonon assisted recombination of hot excitons, is measured directly. By calculating the LO-phonon assisted recombination probability, we obtain the nonthermal energy distribution of excitons and observe directly the energy relaxation of hot excitons during their transport. We find the excitons remain hot during their transport on a length scale of several micrometers. Thus, the excitonic transport on this scale cannot be described by classical diffusion.

Electron Beam Induced Damage of NaNO3 Single Crystals: An Energy, Temperature, and Quantum State Resolved Study

Electron beam induced damage of NaNO{sub 3} single crystals is examined using laser resonance enhanced multiphoton ionization detection of the neutral desorption products, post-irradiation temperature-programmed desorption (TPD), secondary electron emission microscopy (SEEM), and Auger electron spectroscopy (AES). The damage initially involves destruction of the nitrate group and production of O ({sup 3}P{sub J}) and NO ({sup 2}II) fragments with nonthermal energy distributions. Specifically, the O ({sup 3}P{sub J}) J state distribution measured at 100 eV incident electron energy is 5:1.5:0.25 for J = 2:1:0, the NO ({sup 2}II) vibrational state distribution is 1:0.56:0.35:0.40:0.23 for {nu} = 0:1:2:3:4, and the NO ({sup 2}II{sub 1/2,3/2}) rotational distribution has a high population of the upper ({sup 2}II{sub 3/2}) spin-orbit component. Production and desorption of these nonthermal fragments are dominated by the decay of {l{underscore}brace}NO{sub 3}{sup {minus}}{r{underscore}brace}*. At higher electron fluences, thermalized NO, O{sub 2}, and NO{sub 2} are also produced and released, through the NO{sub 2} is a minor product. The authors suggest that the formation and desorption of thermalized NO and O{sub 2} both involve NO{sub 2}{sup {minus}} defect states and unimolecular dissociation of NO{sub 3}{asterisk}. This is supported by the observation that the NO and O{sub 2} yields have the samemore » temperature dependence which is well described by the sum of two Maxwell-Boltzmann type equations with activation energies of 0.16 {+-} 0.03 and 0.010 {+-} 0.004 eV. O{sub 2} gas is also released in post-irradiation thermal cycling from 110 to 440 K with peaks at {approximately}260 and {approximately}340 K. The authors associate the post-irradiation TPD of O{sub 2} with reactions involving O atoms released during thermal decomposition of {l{underscore}brace}NO{sub 2}{sup {minus}}{hor{underscore}ellipsis}O{r{underscore}brace} and ONOO{sup {minus}}. The SEEM image shows damage features, and the AES spectra indicate that the irradiated region is depleted in both nitrogen and oxygen relative to Na. The elemental composition shows Na{sub 2}O as a final product of the NaNO{sub 3} radiation decomposition. The 100 eV electron beam damage cross section is at least {approximately}10{sup {minus}16} cm{sup 2}.« less

Photodissociation of CFCl 3 at 193 nm investigated by photofragment translational spectroscopy

The collisionless photodissociation of CFCl 3 at 193 nm has been studied with the method of crossed laser and molecular beams. The primary dissociation is shown to produce exclusively the fragment pairs CFCl 2 + Cl with a non-thermal translational energy distribution. The average kinetic energy of 32 kcal/mol corresponds to 42% of the available energy and implies an average internal energy of CFCl 2 of 43 kcal/mol. From the recoil anisotropy parameter β = +0.74 ± 0.15 the photoexcitation is inferred to proceed via an E ← A 1 transition polarized perpendicular to the C–F bond. At higher laser fluence a fraction of the nascent CFCl 2 radicals absorbs a further photon and dissociates into CFCl + Cl; the cross section for this secondary process is estimated to be approximately twice as large as that of the primary photodissociation.

General model for electron drift and diffusion in a dense gas

The author presents a general unified model of electron transport in a dense gas of attractive or repulsive scatterers. It attempts to graft the multiple scattering theory of waves, and wave motion in a random medium, plus a newly derived second Ioffe-Regel criterion onto classical Boltzmann theory, with help from drift velocity experiments. The model describes diffusion as well as drift, electric fields strong enough to cause nonthermal energy distributions and high density (nonlinear) effects. Some good agreement is shown with experiment for the mobilities and drift velocities, and a tentative agreement for the diffusion coefficient where experiments are scarce.

The nonthermal stellar dynamics of the globular cluster M15

view Abstract Citations (91) References (45) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Nonthermal Stellar Dynamics of the Globular Cluster M15 Peterson, Ruth C. ; Seitzer, Patrick ; Cudworth, Kyle M. Abstract The velocity dispersion as a function of radius in the globular cluster M15 is derived from measurements of 120 individual stars between 0.1 and 4.6 arcmin of the cluster center, and from the integrated light of the central cusp. The stellar measurements, with an individual accuracy of 1 km/s, indicate a mean cluster velocity of -107.1 + or - 0.9 km/s and a mean velocity dispersion of 9.0 + or - 0.6 km/s. The velocity dispersion inside 12 arcmin varies with radius. Except for its greater velocity gradient, the spectrum of the integrated light of the cusp is indistinguishable from that formed by superposition of the individual M15 giant spectra, demonstrating that the excess light at the center is due primarily to a normal M15 population. The findings indicate a nonthermal energy distribution with substantial heating in the central regions. Publication: The Astrophysical Journal Pub Date: December 1989 DOI: 10.1086/168114 Bibcode: 1989ApJ...347..251P Keywords: Black Holes (Astronomy); Globular Clusters; Stellar Motions; Astronomical Spectroscopy; Binary Stars; Charge Coupled Devices; Mass To Light Ratios; Stellar Models; Velocity Measurement; Astrophysics; CLUSTERS: GLOBULAR; RADIAL VELOCITIES; STARS: STELLAR DYNAMICS full text sources ADS | data products SIMBAD (121) CDS (1)

Observation of nonthermal energy distributions during the impulsive phase of solar flares

The Fe XXV resonance line and dielectronic satellite intensities have been measured as functions of time for several flares recorded by the Naval Research Laboratory crystal spectrometer (SOLFLEX) flown on the US Air Force P78-I spacecraft. The intensity ratios of the Fe XXV resonance line, the Fe XXIV n = 2 satellite line j, and the Fe XXIV n = 3 satellite line d13 indicate that nonthermal electron energy distributions occur during the impulsive phase of the flares. For the electron energies at which the j and d13 satellites are formed (4.7 and 5.8 keV, respectively), the electron energy distributions during the impulsive phase are observed to have a bump or to be nearly flat. For all of the flares that were studied, hard X-ray bursts occurred near the time of the nonthermal distributions observed in the SOLFLEX data.

Excitons and electron-hole plasma in pulse photoexcited ZnTe

Photoluminescence and electronic Raman scattering of undoped ZnTe at 4.2K is observed. Using a pulsed dye laser tuned through the range of the IS polariton, the polariton bands, (A, oX) bound exciton line and the high excitation band can be excited by a two-photon absorption process. The LO-phonon sideband exhibits a non-thermal energy distribution of the polaritons, which does not vary appreciably when polariton-polariton scattering processes occur. Under high intensity excitation Raman scattering by the plasmon-phonon coupled mode is observed, with shift of ω +=34meV. This is taken as evidence for the presence of an electron-hole plasma. The corresponding pair density is ∼9×10 17cm -3 and is found to be independent of excitation intensity in the range of 10 15–10 16 photons/cm 2.

On precursor mechanisms for surface reactions

Abstract Arguments are given in favour of a mechanism for surface reactions involving direct collisions between chemisorbed species and molecules or atoms that are trapped in the neighbourhood of the surface but have not thermalized. Where such “hot precursors” are involved, the distinction between the classic Eley-Rideal and Langmuir-Hinshelwood mechanisms is illdefined. Characteristic features of precursor mechanisms are that they (i) may lead to a non-thermal energy distribution of products, and (ii) will strongly influence reaction rates of, e.g., catalytic reactions.

On precursor mechanisms for surface reactions

Arguments are given in favour of a mechanism for surface reactions involving direct collisions between chemisorbed species and molecules or atoms that are trapped in the neighbourhood of the surface but have not thermalized. Where such “hot precursors” are involved, the distinction between the classic Eley-Rideal and Langmuir-Hinshelwood mechanisms is illdefined. Characteristic features of precursor mechanisms are that they (i) may lead to a non-thermal energy distribution of products, and (ii) will strongly influence reaction rates of, e.g., catalytic reactions.

On precursor mechanisms for surface reactions

Arguments are given in favour of a mechanism for surface reactions involving direct collisions between chemisorbed species and molecules or atoms that are trapped in the neighbourhood of the surface but have not thermalized. Where such “hot precursors” are involved, the distinction between the classic Eley-Rideal and Langmuir-Hinshelwood mechanisms is ill-defined. Characteristic features of precursor mechanisms are that they (i) may lead to a nonthermal energy distribution of products, and (ii) will strongly influence reaction rates of, e.g., catalytic reactions.