FIR Range Research Articles

Characterizing Balsam Woolly Adelgid Infestations and Associated Tree Mortality in Idaho

Abstract Balsam woolly adelgid, Adelges piceae (BWA), is a nonnative insect that has invaded much of the true fir range in North America, reducing host tree growth and causing mortality. Here, we describe a field study to characterize BWA infestation and effects on host trees in Idaho from the onset of infestation within twenty-eight sites with repeated surveys in 2008, 2013, and 2018. Declining tree health was categorized into five BWA damage classes based on the percent of the tree crown–expressing symptoms caused by BWA. Between 2008 and 2018, BWA presence increased across most sites regardless of host species, with an average of 48% (0.1%–100%) host trees per acre being infested. Severe damage or mortality of true fir from BWA occurred across thirteen sampled forest habitat types, including those representing harsh, high elevations. Although a significantly greater proportion of subalpine fir died than grand fir by 2018, BWA caused grand fir mortality. All diameter size classes became infested with BWA, including seedlings, and BWA caused mortality regardless of tree diameter. This assessment provides baseline data for a deeper analysis of insect, host, stand, and environmental interactions that may elucidate factors driving severe stand mortality. Study Implications Balsam woolly adelgid (BWA) is a cryptic, nonnative, and chronically lethal insect of true firs that is frequently overlooked until tree health substantially declines. Therefore, it is often not considered a serious damage agent during forest management planning until after severe damage has occurred across a stand. The BWA damage classification, modified from Spiegel et al. (2013), may be applied during stand exams. This simple and effective five-tiered classification system can be used to categorize BWA damage within individual trees or stands based on the collective symptoms caused by the insect. Feeding by BWA can ultimately result in stand-level mortality of both over- and understory fir and may require artificial regeneration to restore forest function. Fir regeneration was abundant at most BWA-damaged sites; however, seedling-sized firs were often heavily gouted from BWA to levels that will prevent them from growing into seed-bearing trees. Reported levels of mortality caused by BWA within 10 years of infestation and forest habitat type associations can be referenced for making management decisions for not-yet or recently infested stands.

The first Polish provenance experiments with silver fir Abies alba Mill.

Abstract Silver fir Abies alba Mill. provenance trials started in Poland a few years after Pavari (1951) proved that the origin of this tree species influences its genetic variability. Further confirmation came from provenance trials, which selected provenances for cultivation in Denmark and showed provenance-dependent genetic variability even within a relatively small area such as the Czech Republic. The Polish trial, started in 1960, compared 6 provenances from the West and Central Carpathian region (4 from Poland, 2 from Slovakia) and 3 from the Hercinic region (Czech Republic). The trial was established in the Experimental Forests of the Warsaw University of Life Sciences in Rogów, at the northern border of the natural silver fir range. Results from the nursery stage experiments proved the existence of latitudinal and altitudinal clines based on data for seed weight, height growth, number of terminal buds as well as bud and needle development. The Polish provenance ‘Stary Sącz’ and two Slovak provenances, ‘Čierný Váh’ and ‘Beňuš’, were early flushing, whereas the Polish provenance ‘Rogów’ behaved differently and was late flushing. Even at the nursery stage, the positive influence of tree selection on height growth and progeny characteristics of the two Czech provenances was evident. The Carpathian provenances were furthermore evaluated according to the index of cultivation and breeding: very good – ‘Rogów’; good ‘ŚPN (Świętokrzyski PN)’, ‘Stary Sącz’ and ‘Skarżysko’; poor – ‘Čierný Váh’ and ‘Beňuš’.

Theoretical and experimental study of ion-exchange process on zeolites from 5-1 structural group

In this work the DFT calculations were carried out by means of Gaussian09 program for chosen model cluster—mor Composite Building Unit of zeolites structures. Vibrational frequencies computations and infrared spectra were obtained subsequently for above model. The results of calculations have been compared with IR (MIR and FIR range) spectroscopic studies of zeolites belonging to 5-1 structural group (mordenite and ferrierite) after heavy metal cations (Ag+, Zn2+, Cd2+, Pb2+, and Cr3+) immobilization. Changes in intensities and positions of the bands corresponding to the characteristic ring and Me–O vibrations have been observed. These rings occur in pseudomolecular complexes (built of [SiO4] and [AlO4] tetrahedra) which constitute the secondary building units and form zeolite framework. Based on the results of DFT method calculations, normal vibrations of the 5-1 unit terminated by different cations (Na+, K+) have been visualized. Obtained results have been applied for interpretation of experimental spectra of selected zeolites. The most significant changes have been determined in the region of pseudolattice vibrations (800–500 cm−1), as well as Me–O vibrations (below 400 cm−1). It was proven those cations’ sorption causes changes in the experimental spectra of zeolites. Sorption has been conducted on monoionic forms of mordenite and ferrierite. Based on the results of the sorption/desorption experiments, the proportion of ion-exchange to chemisorption in the process and the effective cation exchange capacity of the individual samples have been estimated. Results of AAS studies have been compared with those obtained by vibrational (IR and Raman) spectroscopy. Changes in intensities and positions of the bands corresponding to the characteristic ring vibrations, due to the immobilization of heavy metal ions, have been observed.

Dust emission in star-forming dwarf galaxies: General properties and the nature of the submm excess

We studied the global characteristics of dust emission in a large sample of emission-line star-forming galaxies. The sample consists of two subsamples. One subsample (SDSS sample) includes ~4000 compact star-forming galaxies from the SDSS, which were also detected in all four bands at 3.4, 4.6, 12, and 22 mum of the WISE all-sky survey. The second subsample (Herschel sample) is a sample of 28 compact star-forming galaxies observed with Herschel in the FIR range. Data of the Herschel sample were supplemented by the photometric data from the Spitzer observations, GALEX, SDSS, WISE, 2MASS, NVSS, and FIRST surveys, as well as optical and Spitzer spectra and data in sub-mm and radio ranges. It is found that warm dust luminosities of galaxies from the SDSS sample and cold and warm dust luminosities of galaxies from the Herschel sample are strongly correlated with Hbeta luminosities, which implies that one of the main sources of dust heating in star-forming galaxies is ionising UV radiation of young stars. Using the relation between warm and cold dust masses for estimating the total dust mass in star-forming galaxies with an accuracy better than ~0.5 dex is proposed. On the other hand, it is shown for both samples that dust temperatures do not depend on the metallicities. The dust-to-neutral gas mass ratio strongly declines with decreasing metallicity, similar to that found in other studies of local emission-line galaxies, high-redshift GRB hosts, and DLAs. On the other hand, the dust-to-ionised gas mass ratio is about one hundred times as high implying that most of dust is located in the neutral gas. It is found that thermal free-free emission of ionised gas in compact star-forming galaxies might be responsible for the sub-mm emission excess. This effect is stronger in galaxies with lower metallicities and is also positively affected by an increased star-formation rate.

Application of IR spectra in the studies of zeolites from D4R and D6R structural groups

This work presents results of FT-IR spectroscopic studies (MIR and FIR range) of zeolites (belonging to D4R and D6R structural groups) after heavy metal cations (Ag+, Cu2+, Cd2+, Pb2+, Zn2+, Ni2+ and Cr3+) immobilization. Sorption has been conducted on monoionic forms of synthetic zeolite A (LTA) and Y (FAU) as well as on natural chabazite (CHA).It was proven that those cations’ sorption causes changes in the spectra of the zeolites. Changes in intensities and positions of the bands corresponding to the characteristic ring and MeO vibrations have been observed. These rings occur in pseudomolecular complexes (built of alumino- and silicooxygen tetrahedra) which constitute the secondary building units (SBU) and form spatial framework of the zeolite. Based on the results of DFT method (B98 HF 6–31G(d)) calculations, normal vibrations of the SBU terminated by different cations (Na+, K+) have been visualized. Obtained results have been applied for interpretation of experimental spectra of selected zeolites. The most significant changes have been determined in the region of pseudolattice vibrations (800–550cm−1). On the other hand, an introduction of heavy metal cations into the structure of zeolites has caused the considerable modification of bands due to MeO vibrations in FIR spectra (below 400cm−1).In both cases systematic changes connected with the type of cation (its chemical character) have been revealed. Based on changes in the spectra due to immobilization of heavy metal ions, a scale of sorption can be established.

Dust emissivity variations in the Milky Way

Dust properties appear to vary according to the environment in which the dust evolves. Previous observational indications of these variations in the FIR and submm spectral range are scarce and limited to specific regions of the sky. To determine whether these results can be generalised to larger scales, we study the evolution in dust emissivities from the FIR to mm wavelengths, in the atomic and molecular ISM, along the Galactic plane towards the outer Galaxy. We correlate the dust FIR to mm emission with the HI and CO emission. The study is carried out using the DIRBE data from 100 to 240 mic, the Archeops data from 550 mic to 2.1 mm, and the WMAP data at 3.2 mm (W band), in regions with Galactic latitude |b| < 30 deg, over the Galactic longitude range (75 deg < l < 198 deg) observed with Archeops. In all regions studied, the emissivity spectra in both the atomic and molecular phases are steeper in the FIR (beta = 2.4) than in the submm and mm (beta = 1.5). We find significant variations in the spectral shape of the dust emissivity as a function of the dust temperature in the molecular phase. Regions of similar dust temperature in the molecular and atomic gas exhibit similar emissivity spectra. Regions where the dust is significantly colder in the molecular phase show a significant increase in emissivity for the range 100 - 550 mic. This result supports the hypothesis of grain coagulation in these regions, confirming results obtained over small fractions of the sky in previous studies and allowing us to expand these results to the cold molecular environments in general of the outer MW. We note that it is the first time that these effects have been demonstrated by direct measurement of the emissivity, while previous studies were based only on thermal arguments.

Calculable blackbody radiation as a source for the determination of the spectral responsivity of THz detectors

The spectral responsivity of the detector is important for the layout and quantitative interpretation of spectroscopic experiments. In the terahertz (THz) spectral range the knowledge of the total (integral) responsivity of a detector, as well as its spectral distribution, is often insufficient. PTB determined the spectral irradiance responsivity of two THz detectors, a pyroelectric DLATGS detector working at room temperature and a silicon-composite bolometer working at 4 K, in the wavelength range from 62 µm (4.82 THz) to 1340 µm (0.22 THz) with temperature radiation from blackbody radiators. Our approach is to use two THz cavity radiators in combination with THz bandpass filters to provide calculable spectral irradiances, according to Planck's law of radiation, at several wavelength bands in the THz spectral range. One cavity radiator is working at an adjustable fixed temperature in the range from 15 °C to 90 °C while the other cavity radiator operates at LN2 temperature. The radiation of the two cavity radiators is alternately imaged on the detector via a gold-coated chopper wheel. Hereby the background radiation is cancelled and also the necessary modulation for the lock-in detection is provided. The cavity of the high temperature radiator is coated with a dedicated paint providing high wall emissivity in the FIR and THz spectral range to ensure true blackbody behaviour of the radiator. The bottom of the low temperature radiator consists of THz absorber foam providing hereby also nearly blackbody behaviour. All individual filters and, additionally, the employed filter combinations are characterized for their transmittance in the entire wavelength range from 0.8 µm to 1700 µm to obtain a precise knowledge of the transmitted blackbody spectrum. The very reproducible results indicate that this setup allows a fast, simple and reliable determination of the spectral responsivity of THz detectors. In a next step, the uncertainty of this technique will be further evaluated and investigations will be extended to other types of detectors (e.g. LiTaO3 detectors and Golay cells).

A model for far-infrared and millimeter interstellar dust emission

Good knowledge of the far-infrared and millimeter emission from dust in the interstellar medium is important to get reliable estimates of the dust mass, to trace and understand the evolution of pre-stellar structures, and to accurately subtract the foreground emission in the cosmological background anisotropy measurements. Up to now the modeled dust emission profile in FIR and millimeter wavelength range is deduced from the wings of some mid-infrared fundamental lattice-resonances inside the silicate material, which is known to be the dominant constituent of this dust component. However recent astronomical observations have shown that the dust emission profile could be significantly more complicated than expected. In addition, spectroscopic studies in the laboratory on analogues of amorphous interstellar grains have revealed that additional processes can occur in that spectral range, which are strongly temperature-dependent. We propose a new model for far-infrared and millimeter dust emission which takes into account results from the solid state physics, used to interpret these laboratory data. This model explicitly incorporates the effect of the disorder in the internal structure of the dust grain. We show that this model can give a satisfactory interpretation for the astronomical observations. It opens new perspectives to derive some new dust characteristics from the shape of the dust emission spectrum.

The diversity of chloroplast microsatellite loci in Siberian fir (Abies sibirica Ledeb.) and two Far East fir species A. nephrolepis (Trautv.) Maxim. and A. sachalinensis Fr. Schmidt

The genetic variability in 29 populations of Abies sibirica, three of A. nephrolepis, and seven of A. sachalinensis was studied using SSR markers of chloroplast DNA. Stable amplification and polymorphic products were obtained using primer pairs Pt71936 and Pt30204 (with nine and forteen alleles, respectively) of 10 pairs. Totally, 70 haplotypes were found, 43 in A. sibirica, 49 in A. sachalinensis, and 31 in A. nephrolepis. The highest values of genetic diversity parameters were observed in A. sachalinensis, and the lowest in A. nephrolepis. The Siberian fir differs from Far East species by the uneven multimodal frequency distributions of allele length in both cpSSR loci, which is explained by the presence of few separated from each other dominating haplotypes. This fact indicates that A. sibirica and the Far East species have different demographic histories. In A. sibirica, the proportion of diversity between populations in the total genetic diversity, calculated taking into account the differences between haplotypes (R(ST)) was 8.34% and 4.42% without accounting for haplotypes differences (R(ST) > G(ST), P= 0.01). The pairwise G(ST) correlate significantly with geographic distances between the populations A. sibirica and with genetic distances D calculated from allozyme data. No such correlations were found with the R(ST) parameter. The results of cpSSR variability analysis strongly support the conclusions inferred from allozyme data: several geographic groups of comparatively genetically close populations are identified, which may be explained by the invasion of colonization of the present-day Siberian fir range.

Structure and properties of tecto-gallosilicates II. Sodium chloride, bromide and iodide sodalites

The crystal structures of the gallosilicate sodalites Na8[GaSiO4]6Cl2, Na8[GaSiO4]6Br2and Na8[GaSiO4]6I2were refined from X-ray powder data in the space groupP-43n:a= 894.70 pm,V= 0.7162 nm3,RWP= 0.066,RP= 0.050,RI= 0.011,a= 900.83 pm,V= 0.73102 nm3,RWP= 0.066,RP= 0.051,RI= 0.016 anda= 908.36 pm,V= 0.74951 nm3,RWP= 0.050,RP= 0.036,RI= 0.013 for 4000 data points and 14 variable positional parameters in each case for the chloride, bromide and iodide compound, respectively. The gallium and silicon atoms on the tetrahedral framework positions are totally ordered, the halide anions were found at the centre of the sodalite cage coordinated by four sodium atoms. The recorded infrared and Raman spectra show absorption bands typical for the sodalite structure, but indicate also clearly the difference between chloride, bromide and iodide incorporation in the sodalite cage by different absorption band in the FIR range. Heating X-ray investigations show the expected increases of lattice parameters for all three sodalites with increasing temperature and no phase transition was detected. But for the freshly prepared bromide sample a different nearly linear increase of the lattice parameter was observed up to 770 K and above 870 K with an invariant behaviour between these temperatures. The tilt and T—O—T angle as well as the interatomic Si—O and Ga—O distances show an expected temperature dependent behaviour as found by Rietveld calculations of the high-temperature X-ray data. The angles in the tetragonal distorted SiO4tetrahedra show values comparable to those found in alumosilicate sodalites but seem to be temperature dependent. Additionally, the corresponding GaO4angles indicate a disappearance of the tetragonal tetrahedron distortion around the temperature where the discontinuity was observed for the lattice parameter. The GaO4tetragonal tetrahedron distortion is close to zero during the formation of the framework which leads to different distortion direction. This different distortion direction could be relaxed by heating the sample or a self relaxing occurs within several months at room temperature.

Modelling the damage status of silver fir trees ( Abies alba Mill.) on the basis of geomorphological, climatic and stand factors

The paper investigates the possibility of assessing damage (health status) of silver fir ( Abies alba Mill.) using multivariate regression models in the function of geomorphological, climatic and stand factors. Research was carried out in beech-fir forests ( Abieti-Fagetum), on limestone-dolomite substrate, in the Dinaric part of the silver fir range in the Republic of Croatia. A general linear modelling method was used, where square terms and interaction terms (multiplication products) of original variables were treated as independent linear predictors. Twenty-seven separate models (all of them with significant part of explained fir damage variability) were developed regarding the different subsets of input data, different subsets of independent variables and different model design. Some of these models could be preliminary used for spatial predicting and mapping of fir damage in a frame of raster-GIS, for entire area of Dinaric part of Abieti-Fagetum in Croatia.

Far-infrared and submillimetre observations of the Crab nebula

We present FIR and sub-mm images of the Crab nebula, taken with ISOPHOT on board ISO and with the SCUBA on the JCMT. The ISOPHOT observations were made at 60, 100, 170 micron, with FWHM of equivalent area Gaussian beams of 44, 47 and 93 arcsec, respectively. The 850 micron SCUBA image has a Gaussian FWHM of 17 arcsec. The 60 and 100 micron images show clear excess of emission above that expected from an extrapolation of the synchrotron spectrum of the Crab nebula from lower frequencies. The ISOPHOT images reveal that about half this excess is attributable to two peaks, separated by approximately 80 arcsec. We also present spectra taken using the LWS on board ISO, which show that the FIR excess is not due to line emission. The lower resolution 170 micron image does not show any excess emission. These findings are consistent with a picture in which the FIR excess is due to emission from a small amount of warm dust which radiates predominantly at 60 and 100 micron micron but not at 170 micron, and which is superimposed on a synchrotron spectrum which gradually steepens towards shorter wavelengths throughout the FIR and MIR spectral range. The dust geometry is consistent with a torus of diameter approximately 0.8 pc created by the supernova progenitor, superimposed upon a broadly distributed component which may be supernova condensates in the filaments. The dust-to-gas ratio in the filaments is comparable to the interstellar value. To study spectral index variations in the radio synchrotron emission we compared the 850-micron image with a 20-cm VLA image. These images are very similar, implying that there is little variation in spectral index across the face of the remnant between these wavelengths.

Heterojunction interfacial workfunction internal photoemission detectors for use at 8–20 [micro sign

Heterojunction interfacial workfunction internal photoemission (HEIWIP) detectors have already been demonstrated for use in the FIR range with cutoff wavelengths (λc) up to 85 µm. An interesting feature of these detectors is their strong response in the 8–20 µm range. Initial results are reported on HEIWIP detectors operating in the 8–20 µm range. The unoptimised detectors had a peak responsivity of 1.8 A/W at 15.2 µm at 4.2 K. HEIWIPs could be an alternative to already available detectors especially when optimised for higher temperatures. λc can be tailored by changing the Al concentration in the barrier. Responsivity of HEIWIPs can be selectively optimised by using the cavity mechanism and adjusting the Al fraction. It should also be possible to enhance the responsivity by changing the doping concentrations of the detectors.

QUANTUM STRUCTURES FOR FAR-INFRARED DETECTION

FIR photon detector development starting from the extrinsic detectors for LWIR to FIR wavelengths are presented. Several other types of IR detectors, including the cut-off wavelength extension into the FIR range for quantum well infrared photodetectors (QWIPs), are summarized. Efforts in developing p-GaAs homojunction interfacial workfunction internal photoemission (HIWIP) far-infrared detectors and the most reason developments on GaAs/AlGaAs Heterojunction interfacial workfunction internal photoemission (HEIWIP) far-infrared detectors are presented.

The complex refractive index of limestone particles: an extension to the FIR range for Mars applications

Theoretical studies and numerical models of the atmosphere and surface of Mars need the knowledge of the optical constants of candidate materials for Martian dust, in a wavelength range as wide as possible. Limestone, as a carbonate-bearing material, is commonly considered a likely component particularly important for its links with the climate evolution and water resources on Mars. In a previous paper, we reported the complex indices of refraction of submicron particles of limestone, derived from laboratory transmission spectra in the wavelength range 3.5– 20 μm by means of the dispersion theory. In this work we present the same quantities in a wider spectral range extending from 1.5 up to 62.5 μm . Such an extension is particularly important since limestone, as well as other carbonates, has some of its characteristic features between 20 and 50 μm . Our data are discussed and compared with those given by other authors and obtained with a different method (i.e. reflection measurements) on samples consisting of pressed pellets of randomly oriented calcite grains. As in the case of the previous work, our results point out, again, that the extinction spectra of submicron particles can be better reproduced using optical constants directly obtained in the laboratory for particulate materials. Finally, the extinction and emission properties of limestone grains are used in order to tentatively identify carbonates on Mars and to understand whether these materials are present in the Martian aerosol or on the surface. Our results seem to suggest that, limestone particles can be a minor component of the atmospheric dust rather than of the surface regolith, provided that some bands observed in the Martian spectra will be finally ascribed to such material.

Photometric Investigation of the Peculiar Galaxy NGC 7468 (Mrk 314)

The results of a photometric investigation of the peculiar galaxy NGC 7468 are presented. Based on its integrated characteristics, NGC 7468 is a relatively small galaxy of a late morphological type, resembling the Large Magellanic Cloud (LMC). The differences of NGC 7468 from the LMC (bluer color indices, an increased luminosity, an increased H I abundance, and strong emission in the FIR range) may be related to a higher rate of star formation in it. The increased star-forming activity in the central regions of NGC 7468 and its other properties may be related to a gravitational interaction with a small neighboring galaxy, the remnants of which are now observed as a companion.

Far-Infrared Spectroscopy of Shallow Acceptors in Strained Ge/GeSi Quantum Well Heterostructures

Far-infrared photoconductivity spectra of strained multi-quantum well Ge/Ge1—xSix (≈︂ 0.1) heterostructures resulting from the excitation of shallow acceptors were investigated. The spectra are shown to be shifted to the long-wavelength end of the far-infrared range if compared with acceptors in bulk p-Ge due to the splitting of light and heavy holes subbands in Ge layers owing to the “built-in” deformation and size quantization. The shallow acceptor spectra in bulk germanium under uniaxial tension, that is “equivalent” to the deformation of Ge layers in the heterostructures, were calculated by the variational technique; the results were used for the interpretation of the experimental data. Ge/GeSi heterostructures are shown to be a sensitive photoelectric detector for the long wavelength end of FIR range.

First lasings at IR and FIR range using the FELI FEL facility 4

First lasing at 18 μm was achieved by using a 2.7 m long hybrid-type undulator (undulator 4) for far-infrared FELs and a 6.72 m long optical cavity installed at the 33 MeV beam line of the downstream of the FEL facility 1 (FEL-1). We are challenged at two-color FEL oscillation in mid-infrared range using the undulator 1 (λ u =3.4 cm) and in far-infrared range using the undulator 4 ( λ u=9 cm). At first, a 30 MeV, 40 A beam passed through the undulator 1 without lasing is transported using a Q F Q D BQ F Q D BQ F Q D Q F system and was used for lasing at the undulator 4. However, six pairs of steering coils had to be attached on the beam duct to reduce the deviation of the electron beam trajectory due to the vertical field distribution induced by the built-in electromagnets and the steering coils attached on the beam duct increased the gap up to 52 mm. Therefore, the hybrid-type undulator was replaced by a new Halbach-type one ( λ u=8 cm, N=30) after the first lasing at 18 μ m on 24 October 1996. The new FEL facility 4 was installed in the middle of December and first lasing at 18.6 μ m was achieved on December 26 using 33 MeV, 40 A beam passed through the undulator 1 without lasing. This paper describes first lasings at IR and FIR range using a Halbach-type undulator (undulator 4) and 33 MeV, 40 A beam passed through the undulator 1 without lasing and a challenge at two-color FEL oscillation using the FEL facilities 1 and 4.

Elaboration, Characterisation, and Magnetic Properties of Cobalt Fine Particles

Nanoparticles of cobalt have been prepared by an original method using the decomposition under hydrogen of an organometallic precursor in the presence of a stabilizing polymer. Two colloids (C1, C2) have been obtained by changing the organometallic concentration in the polymer. Observation by HRTEM and WAXS showed that Co particles have diameter around 1.5 nm (C1) and 2 nm (C2). They are well isolated and regularly scattered in the polymer, with an original bcc structure. These particles show a superparamagnetic behavior above the blocking temperature (T B ). Analysis of the magnetization curves above T B confirms the very weak volume dispersion of the particles centered around 150±10 atoms (C1) and 310±20 atoms (C2), and their homogeneous distribution in the polymer observed by HRTEM. Enhanced effective anisotropy energy with uniaxial symmetry has been deduced from magnetization and ferromagnetic resonance measurements in the FIR range (100-700 Ghz). Magnetization at 5 K seems to saturate in fields up to 5 T leading to an enhanced mean magnetic moment per atom, = 1.94±0.05 μ B for the smallest particles. These values still increase in field up to 35T reaching = 2.1±0.1 μ B (C1), exhibiting a canted spin structure due to high surface anisotropy. This set of data allows us to conclude that the enhanced magnetization, its increase with applied magnetic field, and the enhanced effective magnetic anisotropy, these effects being more significant with decreasing size, are associated to the large influence of the surface atoms.

Evidence of the Superposition of Drude Type and Hopping Type Transport in Boron-Rich Solids

The dielectric function of the boron-rich solids in the FIR range is analyzed on the basis of their optical reflectivity spectra, which exhibit obviously typical, strongly increasing slopes with decreasing frequencies. It is shown that these slopes can be quantitatively described, when a superposition of Drude type and hopping type parts for the dynamical conductivity is assumed. The corresponding fits were simultaneously made for the real and imaginary parts of the dielectric function to achieve unambiguous parameters. The obtained results are consistent, e.g., with the DC conductivity of these semiconductors, and in particular in the case ofβ-rhombohedral boron with the known energy band scheme and the related electronic properties. The bipolaron hopping model of the electronic transport in boron carbide turns out to be inappropriate.