Resonant plasma excitation by single-cycle THz pulses

In this paper, an alternative perspective for the generation of millimetric high-gradient resonant plasma waves is discussed. This method is based on the plasma-wave excitation by energetic single-cycle THz pulses whose temporal length is comparable to the plasma wavelength. The excitation regime discussed in this paper is the quasi-nonlinear regime that can be achieved when the normalized vector potential of the driving THz pulse is on the order of unity. To investigate this regime and determine the strength of the excited electric elds, a Particle-In-Cell (PIC) code has been used. It has been found that by exploiting THz pulses with characteristics currently available in laboratory, longitudinal electron plasma waves with electric gradients up to hundreds MV/m can be obtained. The mm-size nature of the resonant plasma wave can be of great utility for an acceleration scheme in which high-brightness electron bunches are injected into the wave to undergo a strong acceleration. The long-size nature of the acceleration bucket with respect to the short length of the electron bunches can be handled in a more robust manner in comparison with the case when micrometric waves are employed

Some haematochemical parameters of intensively farmed rainbow trout (Oncorhynchus mykiss)

The aim of the present study was a preliminary determination of the metabolic profile (MP) of one of the most economically valuable species on the Italian market. Defining the metabolic profile (MP) of a species is not easy because of many factors affecting the blood parameters, but assessing the normality values is necessary to identify the limits out of which a production or reproduction decrease can happen

Contribution to the definition of the metabolic profile of farmed rainbow trout (Oncorhynchus mykiss)

The haematic outline of 339 rainbow trout (Oncorhynchus mykiss)from two different farms in the Lucca province was studied for a preliminary assessment of the metabolic profile of this species and for the investigation of the influence of some endogenous and exogenous factors on the variability of the studied parameters. The sampling time, as well as the weight, appears to have caused significant variations on most of the parameters analysed. The present study gives the annual means and the seasonal trends for each farm where the study was carried out

Water vapour absorption effects on solar radiation in an Apennine valley from hygrometric measurements of precipitable water taken at various altitudes

Hygrometric ratio measurements were simultaneously taken on six autumn clear-sky days of 1981 and 1982 by employing four Volz sun-photometers and the FISBAT sun-photometer at five stations located at different altitudes along the western slope of the Leo Valley, in the Apennines (Italy). Due to the solar heating of ground, intense upslope breezes forming during the early morning caused the vertical transport of more humid air from the bottom of the valley toward the ridge of the mountain chain. Precise calibration curves of the hygrometric ratio were defined on the basis of criteria suggested by the atmospheric infrared hygrometry technique and using the calibration constants found through an accurate intercomparison procedure. Examining the sun-photometric measurements by means of these calibration curves, precipitable water was determined at all stations, with the frequency of one measurement every 15 minutes from the early morning to one hour after noon. Daily homogeneous time-patterns of precipitable water were defined at the various stations, showing that this quantity varies appreciably during the morning at all stations, sometimes presenting daily increases of more than 40% at the lower stations. Average values of absolute humidity were then determined within the four atmospheric layers defined by the station altitudes, finding that the convective transport of humid air along the valley slopes can produce important variations within the atmospheric layer below the 1.6 km height. For these moisture conditions of the atmosphere, calculations of the time-variations caused by water vapour absorption in the downwelling flux Φ1 of global solar radiation reaching the ground were made at the various stations, as well as of those in the upwelling flux Φ of solar radiation at the top-level of the atmosphere. The results indicate that: i) flux Φ1 can appreciably decrease due to water vapour absorption, by 10 to 20 W m −2 at the highest station of Mt. Cimone and by 70 to 80 W m −2 at the lowest station situated on the bottom of the Leo Valley, and ii) the changes caused by water vapour absorption in the upwelling flux Φ were estimated to range usually between about 5 W m−2 at the Mt. Cimone station and more than 25 W m−2 at the lowest station. In particular, as a consequence of the time-variations in both precipitable water and solar elevation angle, the change ΔΦ caused by water vapour in the instantaneous outgoing flux of solar radiation at noon was found to increase almost linearly as a function of precipitable water throughout the range from 0.8 to 1.8 g cm−2, with an average slope coefficient equal to 12.5 W m−2 per unit variation of precipitable water

Gliding on Ice in search of accurate and cost-effective computational methods for Astrochemistry on Grains: the puzzling case of the HCN isomerization

The isomerization of hydrogen cyanide to hydrogen isocyanide on icy grain surfaces is investigated by an accurate composite method (jun-Cheap) rooted in the coupled cluster ansatz and by density functional approaches. After benchmarking density functional predictions of both geometries and reaction energies against jun-Cheap results for the relatively small model system HCN···(H2O)2, the best performing DFT methods are selected. A large cluster containing 20 water molecules is then employed within a QM/QM′ approach to include a realistic environment mimicking the surface of icy grains. Our results indicate that four water molecules are directly involved in a proton relay mechanism, which strongly reduces the activation energy with respect to the direct hydrogen transfer occurring in the isolated molecule. Further extension of the size of the cluster up to 192 water molecules in the framework of a three-layer QM/QM′/MM model has a negligible effect on the energy barrier ruling the isomerization. Computation of reaction rates by the transition state theory indicates that on icy surfaces, the isomerization of HNC to HCN could occur quite easily even at low temperatures thanks to the reduced activation energy that can be effectively overcome by tunneling

Development and Validation of a Parameter-Free Model Chemistry for the Computation of Reliable Reaction Rates

A recently developed model chemistry (jun-Cheap) has been slightly modified and proposed as an effective, reliable, and parameter-free scheme for the computation of accurate reaction rates with special reference to astrochemical and atmospheric processes. Benchmarks with different sets of state-of-the-art energy barriers spanning a wide range of values show that, in the absence of strong multireference contributions, the proposed model outperforms the most well-known model chemistries, reaching a subchemical accuracy without any empirical parameter and with affordable computer times. Some test cases show that geometries, energy barriers, zero point energies, and thermal contributions computed at this level can be used in the framework of the master equation approach based on the ab initio transition-state theory for obtaining accurate reaction rates.A recently developed model chemistry (jun-Cheap) has been slightly modified and proposed as an effective, reliable, and parameter-free scheme for the computation of accurate reaction rates with special reference to astrochemical and atmospheric processes. Benchmarks with different sets of state-of-the-art energy barriers spanning a wide range of values show that, in the absence of strong multireference contributions, the proposed model outperforms the most well-known model chemistries, reaching a subchemical accuracy without any empirical parameter and with affordable computer times. Some test cases show that geometries, energy barriers, zero point energies, and thermal contributions computed at this level can be used in the framework of the master equation approach based on the ab initio transition-state theory for obtaining accurate reaction rates

Anomalous optical absorption in overdoped cuprates near the charge-ordering instability

We propose an interpretation for the hump observed in the optical conductivity at or below a few hundreds of cm$^{-1}$, in overdoped cuprates like the electron-doped Nd_{2-x}Ce_xCuO_{4-y} at x\gtrsim 0.15 and the hole-doped Bi_2Sr_2CuO_6 and La_{2-x}Sr_xCuO_4. This interpretation is based on the direct excitation of charge collective modes, which become nearly critical in the proximity to a charge-ordering instability. The nearly critical character of these excitations entails a peculiar temperature dependence and a pseudo-scaling form of the lineshapes, which are in agreement with the experimental data.Comment: 5 pages, 3 figure

Dependence of the upward terrestrial radiance within the (3.5–4.0) μm spectral range on thermodynamic and composition parameters of the atmosphere

Calculations of the upward infrared radiance reaching outer space within the (3.5–4.0) μm wavelength range were carried out to define the dependence features of the signals measured by radiometers onboard satellites on the temperature, moisture and composition parameters of the atmosphere. In particular, simulations of upwelling radiance were performed for application to the measurements taken by the AVHRR radiometers mounted aboard the NOAA-7 to NOAA-16 satellites and the SEVIRI instrument mounted aboard the Second Generation Meteosat (MSG-1) satellite launched in 2002. The calculations were made using a modified version of computer code LOWTRAN 7 for a large set of atmospheric vertical profiles of temperature and humidity parameters, each one represented with a set of 324 isothermal layers from sea-level to 100 km height and derived from one of 23 atmospheric models relative to different latitudes and seasons. For all these atmospheric configurations, we determined the temperature deficit ΔT, as given b ythe difference between the surface temperature and apparent emission temperature of the surface, the latter quantity being obtained in terms of black-body emission theory from the satellite measurement of upward radiance. Parameter ΔT was found to depend mainly on the total atmospheric content of water vapour and the shape of the vertical profile of temperature within the ground layer: it was found to vary considerably passing from cases of marked thermal inversions to cases of adiabatic or superadiabatic temperature gradients. Considering sets of atmospheric models where precipitable water was assumed to remain constant, ΔT was found to decrease appreciably as the temperature gradient increases from negative values (in the presence of thermal inversions) to positive ones (for adiabatic and superadiabatic lapse rates at the ground), presenting negative slopes that become gradually more marked as the ground layer depth increases. Considering sets of atmospheric models where the moisture parameters were assumed to vary widely, ΔT was found to change linearly as a function of precipitable water, with slope coefficients varying slowly from positive to negative values, as the temperature gradient increases from negative to positive values. As a consequence of these dependence features, the ratio between ΔT and precipitable water was found to increase as a function of surface temperature, following patterns closely best-fitted by second-order polynomial curves. Dependence features of ΔT on the mean atmospheric concentrations of methane and nitrous oxide were also determined. Similarly, ΔT was found to vary linearly as a function of aerosol optical thickness in the visible for polydispersions of maritime, rural, urban and tropospheric aerosols, presenting the most marked slope in the case of maritime aerosols. An overall procedure is proposed for calculating ΔT, taking into account i) the latitudinal and seasonal conditions of the atmosphere, ii) estimates of ground-level temperature and precipitable water, as derived from satellite and/or ground-based measurements of meteorological parameters, iii) aerosol optical thickness at visible wavelengths, and iv) CH4 and N2O atmospheric concentrations