This study attempts a new identification of mechanisms of secondary ice production (SIP) based on the observation of small faceted ice crystals (hexagonal plates or columns) with typical sizes ...smaller than 100µm. Due to their young age, such small ice crystals can be used as tracers for identifying the conditions for SIP. Observations reported here were conducted in oceanic tropical mesoscale convective systems (MCSs) and midlatitude frontal clouds in the temperature range from 0 to −15◦C and heavily seeded by aged ice particles. It was found that in both MCSs and frontal clouds, SIP was observed right above the melting layer and extended to higher altitudes with colder temperatures. The roles of six possible mechanisms to generate the SIP particles are assessed using additional observations. In most observed SIP cases, small secondary ice particles spatially correlated with liquid-phase, vertical updrafts and aged rimed ice particles. However, in many cases, neither graupel nor liquid drops were observed in the SIP regions, and therefore, the conditions for an active Hallett–Mossop process were not met. In many cases, large concentrations of small pristine ice particles were observed right above the melting layer, starting at temperatures as warm as −0.5◦C. It is proposed that the initiation of SIP above the melting layer is stimulated by the recirculation of large liquid drops through the melting layer with convective turbulent updrafts. After re-entering a super cooled environment above the melting layer, they impact with aged ice, freeze, and shatter. The size of the splinters generated during SIP was estimated as 10µm or less. A principal conclusion of this work is that only the freezing drop-shattering mechanism could be clearly supported by the airborne in situ observations.
It is found that the time of establishing a critical contact angle of wetting the surface of a pressed sample made of polycrystalline quartz powder with different liquids is determined primarily by ...the viscosity of the liquid. It is shown that, in order to determine the critical contact angle of powder materials, it is necessary to record the moment at which the diameter of the base of a liquid droplet on the surface of a powder sample has a maximum value.
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•Depth-resolved atomic structure of Fe and Cr atoms for the Cr/Fe sample was obtained.•A depth resolution of 2-3 Å was reached.•It was shown what chromium oxides were present on the ...surface of the sample.•A mathematical software DLAS was applied for treatment experimental data.
A subnanometric resolution method for studying the local atomic structure of interface and surface of low contrast multilayered nanoheterostructure thin films is applied to the Fe/Cr multilayer sample with GMR (Giant Magnetoresistance) effect. We consider combination of the X-ray reflectivity (XRR) and the Extended X-ray absorption Fine Structure (EXAFS) spectroscopy with angular resolution. The XRR experiment has been carried out according to standard procedure using a specialized X-ray diffractometer «Empyrean» at the Institute of Metal Physics (Ekaterinburg). We have applied a measurement method proposed earlier by V. P. Romanov et al. This approach allowed us to separate the diffuse and pure specular contributions. To determine the concentration depth-profile of element from XRR data, we have implemented the Levenberg-Marquardt (L-M) algorithm for nonlinear inverse problem. Thus, the phase problem for X-ray specular reflectivity has been solving. The EXAFS measurements has been performed using synchrotron facilities (National Research Centre “Kurchatov Institute”). {The Fe and Cr K absorption spectra} were recorded in fluorescence mode with angular resolution. The experimental results for depth-resolved local atomic structure of Fe/Cr multilayer with GMR effect has been obtained. A depth resolution of 2-3 Å was reached. Atomic structure of Fe and Cr atoms located at seven depth points including interface for the Al2O3/Cr(100 Å)/Fe(8 Å)/Cr(10,5 Å)2/Cr(20 Å) multilayered sample was obtained. It was shown what chromium oxides were present on the surface of the sample.
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The aeronautics industry has established that a threat to aircraft is posed by atmospheric conditions of substantial ice water content (IWC) where equivalent radar reflectivity (Ze) does not exceed ...20–30 dBZ and supercooled water is not present; these conditions are encountered almost exclusively in the vicinity of deep convection. Part 1 (Fridlind et al., 2015) of this two-part study presents in situ measurements of such conditions sampled by Airbus in three tropical regions, commonly near 11 km and −43 °C, and concludes that the measured ice particle size distributions are broadly consistent with past literature with profiling radar measurements of Ze and mean Doppler velocity obtained within monsoonal deep convection in one of the regions sampled. In all three regions, the Airbus measurements generally indicate variable IWC that often exceeds 2 g m-3 with relatively uniform mass median area-equivalent diameter (MMDeq) of 200–300 μm. Here we use a parcel model with size-resolved microphysics to investigate microphysical pathways that could lead to such conditions. Our simulations indicate that homogeneous freezing of water drops produces a much smaller ice MMDeq than observed, and occurs only in the absence of hydrometeor gravitational collection for the conditions considered. Development of a mass mode of ice aloft that overlaps with the measurements requires a substantial source of small ice particles at temperatures of about −10 °C or warmer, which subsequently grow from water vapor. One conceivable source in our simulation framework is Hallett–Mossop ice production; another is abundant concentrations of heterogeneous ice freezing nuclei acting together with copious shattering of water drops upon freezing. Regardless of the production mechanism, the dominant mass modal diameter of vapor-grown ice is reduced as the ice-multiplication source strength increases and as competition for water vapor increases. Both mass and modal diameter are reduced by entrainment and by increasing aerosol concentrations. Weaker updrafts lead to greater mass and larger modal diameters of vapor-grown ice, the opposite of expectations regarding lofting of larger ice particles in stronger updrafts. While stronger updrafts do loft more dense ice particles produced primarily by raindrop freezing, we find that weaker updrafts allow the warm rain process to reduce competition for diffusional growth of the less dense ice expected to persist in convective outflow.
Soils of the Ray-Iz Massif, Polar Urals Zhangurov, E. V.; Korolev, M. A.; Dubrovskiy, Y. A. ...
Eurasian soil science,
04/2023, Letnik:
56, Številka:
4
Journal Article
Recenzirano
—
Little-studied soils of larch woodlands, mountainous tundras, and cold alpine barrens of the Polar Urals under different geomorphic conditions have been described, and their classification position ...has been determined using the profile-genetic approach. Morphological, physicochemical, and chemical characteristics of the soil profiles formed on mafic and ultramafic rocks are analyzed. It is shown that dominant soils developing from these rocks under larch stands in the Polar Urals are represented by podzolized and humus-illuvial podburs. Both soils are classified as Entic Podzols (Skeletic) according to the WRB-2015 system. In the mountainous tundra, mucky oxidized-gley gleyzems (Reductaquic Gleysols (Thixotropic)) and gray-humus soils (Skeletic Phaeozems) are formed. In the extreme conditions of cold alpine barrens (900–1033 m a.s.l.), different subtypes of gleyzems (Reductaquic Gleysols and Turbic Gleysols (Abruptic)) are locally developed. Deposition of predominantly aboveground plant litter and its slow mineralization on the mineral surface in these soils lead to the development of raw-humus and peaty horizons with a wide C/N molecular ratio.
A new elementary proof of an estimate for incomplete Kloosterman sums modulo a prime
q
is obtained. Along with Bourgain’s 2005 estimate of the double Kloosterman sum of a special form, it leads to an ...elementary derivation of an estimate for Kloosterman sums with primes for the case in which the length of the sum is of order
q
0.5+
ε
, where
ε
is an arbitrarily small fixed number.
Divisors of a Quadratic Form with Primes Korolev, M. A.
Proceedings of the Steklov Institute of Mathematics,
11/2018, Letnik:
303, Številka:
1
Journal Article, Conference Proceeding
Recenzirano
We obtain an asymptotic formula for the average number of divisors of the quadratic form
A
(
x, y, z
) =
xy + xz + yz
, where
x, y
, and
z
run through prime numbers from the interval
X
<
x,y,z
≤ 2
X
.
The COVID-19 pandemic has brought significant changes in managing of patients with rheumatoid arthritis. Rituximab-treated patients were more susceptible to severe infection. This required a “switch” ...to another genetically engineered drug in the patients with high risk of adverse COVID-19. In this study, we assessed the severity of immune response to SARS-CoV-2 antigens in rituximab-treated patients with rheumatoid arthritis vaccinated with the combined vector vaccine Gam-COVID-Vac. Insufficient formation of the humoral response and a high level of T-cell response to SARS-CoV-2 antigens in this group of patients were revealed. An imbalance of cellular and humoral response may play a role in more severe COVID-19 in rituximab-treated patients with rheumatoid arthritis.
Using the Karatsuba method, we obtain new estimates for Kloosterman sums modulo a prime, which, under certain constraints on the number of summands, are sharper than similar estimates found earlier.
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