2,693 research outputs found
Physical origin of Davydov splitting and resonant Raman spectroscopy of Davydov components in multilayer MoTe2
No full textWe systematically study the high-resolution and polarized Raman spectra of multilayer (ML) MoTe2. The layer-breathing (LB) and shear (C) modes are observed in the ultralow-frequency region, which are used to quantitatively evaluate the interlayer coupling in ML MoTe2 based on the linear chain model, in which only the nearest interlayer coupling is considered. The Raman spectra on three different substrates verify the negligible substrate effect on the phonon frequencies of ML MoTe2. Ten excitation energies are used to measure the high-frequency modes of N-layer MoTe2 (NL MoTe2; N is an integer). Under the resonant excitation condition, we observe N-dependent Davydov components in ML MoTe2, originating from the Raman-active A(1)' (A(1g)(2)) modes at similar to 172 cm(-1). More than two Davydov components are observed in NL MoTe2 for N > 4 by Raman spectroscopy. The N-dependent Davydov components are further investigated based on the symmetry analysis. A van der Waals model only considering the nearest interlayer coupling has been proposed to well understand the Davydov splitting of high-frequency A(1)' (A(1g)(2)) modes. The different resonant profiles for the two Davydov components in 3L MoTe2 indicate that proper excitation energy of similar to 1.8 - 2.2 eV must be chosen to observe the Davydov splitting in ML MoTe2. Our work presents a simple way to identify layer number of ultrathin MoTe2 flakes by the corresponding number and peak position of Davydov components. Our work also provides a direct evidence from Raman spectroscopy of how the nearest van der Waals interactions significantly affect the frequency of the high-frequency intralayer phonon modes in multilayer MoTe2 and expands the understanding on the lattice vibrations and interlayer coupling of transition metal dichalcogenides and other two-dimensional materials.National Basic Research Program of China [2013CB921901, 2012CB932703]; National Natural Science Foundation of China [11225421, 11434010, 11474277, 61125402, 51172004, 11474007]SCI(E)[email protected]; [email protected]
The Yakubovich S-Lemma Revisited: Stability and Contractivity in Non-Euclidean Norms
No full textThe celebrated S-Lemma was originally proposed to ensure the existence of a
quadratic Lyapunov function in the Lur'e problem of absolute stability. A
quadratic Lyapunov function is, however, nothing else than a squared Euclidean
norm on the state space (that is, a norm induced by an inner product). A
natural question arises as to whether squared non-Euclidean norms
may serve as Lyapunov functions in stability problems. This
paper presents a novel non-polynomial S-Lemma that leads to constructive
criteria for the existence of such functions defined by weighted
norms. Our generalized S-Lemma leads to new absolute stability and absolute
contractivity criteria for Lur'e-type systems, including, for example, a new
simple proof of the Aizerman and Kalman conjectures for positive Lur'e systems
Administrative procedures and development of citizens' rights in public functions: comparative law reflections
No full textMexico: 30 years of neoliberal paradigm
No full textInterview with Vladimir Mikhailovich Davydov, Doctor of Economics, Corresponding Member of the Russian Academy of Sciences, Scientific Director of the Institute of Latin America of the Russian Academy of Sciences, Director of the Institute of Latin America of the Russian Academy of Sciences (1995-2017). Being one of the leading specialists in Latin American studies in Russia, Dr. Davydov is the author of more than 350 research papers. His works made a huge contribution to the study of socio-economic and political processes taking place in Latin America, as well as to the development of Iberoamericanism in Russia.The interview was conducted by: A.A. Habarta
Umbilicaria platyrhiza Davydov 2022, sp. nov.
No full textUmbilicaria platyrhiza Davydov, sp. nov. (Figure 1, 2) MycoBank no. 841496 Similar to U. crustulosa, differing by apothecia with a single gyrus of sterile tissue, grey-brown to black lower surface with flattened to strap-like rhizinomorphs, smaller ascospores, and by producing umbilicaric acid. Type:— TURKEY. Prov. Izmir (35): southern slope of Yamanlar Dað, small valley N of Karþiyaka, 38°30’ N, 27°07’ E, elev. 125 m, on vertical siliceous rocks. 30 June 2001, V. John [V. John: Lichenes Anatolici Exsiccati, 171, as U. spodochroa Hoffm.] (holotype, M!, isotypes examined in ALTB! ex GZU, GZU!, LE L–1933!). Sequences of the holotype: ITS: KY947760; RPB2: KY972608; mtLSU: KY947904. Thallus 2–4 cm in diam. and 0.2–0.3 mm thick, umbilicate, monophyllous. Upper surface pale to dark grey, sometimes with a brown or violet tinge, lighter at the center, minutely rimose, pruinose, more rough and partly radially folded in the center, sometimes with branched to strap-like rhizinomorphs (Fig. 2C). Lower surface usually dirty ochre-brown to grey-brown and black, darker towards the center, rimose to coarsely papillate with abundant to scarce rhizinomorphs. Rhizinomorphs simple to few times branched under the sharp angle, often flattened to strap-like, ca. 1 mm long; colored at the base the same as the lower surface, and getting darker toward the tips, with rimose to papillate surface (Fig. 2A–B). Thalloconidia absent. Upper cortex paraplectenchymatous, brownish in the outer part and hyaline in the inner part, 25–60 μm, epicortex 12–30 μm, algal layer continuous, 38–100 μm thick, algae Trebouxioid, with cells (5–)7–10–13(–15) μm in diam., medulla colourless, more or less loose, 75–95 μm thick, lower cortex colourless, scleroplectenchymatous, 25–80 μm thick, including a colourless inner layer 20–34 μm thick and a brown outer layer 15–40 μm thick. Apothecia frequent at the periphery of thalli, ca. 1 mm in diam., disc first flat, with age becoming convex, i.e. broadly cone-like with a single central protruding gyrus of sterile tissue (Fig. 2D) with cells 5–9 μm diam. (Fig. 2E); epihymenium brown, 13–25 μm thick; hymenium yellowish 65–92 μm thick, hypothecium ochre to light brown, 40–130 μm thick; excipulum inner part yellowish, outer part brown; paraphyses septate, branched, 2.5 μm thick, sometimes slightly thickened at the tips, up to 3 μm; asci 50–60 × 20–30 μm; ascospores hyaline, simple, (14.0–) 16.0–17.5–18.5(–20.0) × (9.0–)9.5–11.5–13.0(–17.5) μm (N=60). Pycnidia at the periphery of thalli, 125–175 μm in diameter, covered by cortex and algal layer, with black prominent ostiole, the wall brown, 10 μm thick, pycnoconidia bacilliform, 3–4×1 μm. Chemistry: gyrophoric (major), umbilicaric (minor), and lecanoric (minor) acids detected by TLC and HPLC; medulla K–, C+ red, KC+ red, Pd–, UV–. Etymology: platyrhiza derived from Greek πλατύς – ‘wide, flat’, and ρίζα – ‘root’, with reference to the flattened rhizinomorphs. Ecology: Umbilicaria platyrhiza grows on siliceous rocks in maritime territories. Distribution: The species is so far known from only two localities in coastal territories of the Aegean Sea (Turkey, Izmir) and Black Sea (Bulgaria, Burgas). Additional specimens of Umbilicaria platyrhiza examined : BULGARIA. Burgas: loco Veselita skala dicto supra fl. Ropotamo prope inter Sozopol und Primorsko, alt. 30 m s. m. Ad saxa andesitica, 21 August 1977. A. Vežda [Exsicc. Lich. Sel. no. 1531, as U. spodochroa] (GZU –324242!, GZU –s.n.!, ALTB! ex GZU).Published as part of Davydov, Evgeny A., 2022, Umbilicaria platyrhiza-a new Mediterranean endemic species of the subgenus Papillophora (Umbilicariaceae, lichenized Ascomycota), pp. 143-148 in Phytotaxa 533 (2) on page 144, DOI: 10.11646/phytotaxa.533.2.3, http://zenodo.org/record/603631
Heroin abusers’ performance on the Tower of London Test relates to the baseline EEG alpha2 mean frequency shifts
No full textPlanning function deficit is the most consistent finding in neuropsychological studies of heroin addicts. The performance on the Tower of London Test (TLT) correlated with the duration of daily heroin abuse (DDHA) in our previous study. Alpha2 mean frequency in anterior/central derivations was also predicted by DDHA in the same patient population. This retrospective study was undertaken in order to understand better the relationships between observed neurological deviations in heroin abusers. Thirty-three heroin addicts and 12 healthy males were evaluated with 14 neuropsychological tests and resting eyes-closed electroencephalography (EEG). Multivariate tests showed that performance on the difficult (five-move) problems of TLT was strongly predicted by the EEG alpha2 mean frequency shifts, and these relationships were generally mediated by chronic heroin length. However, post-hoc analyses at separate leads demonstrated that the relationships between cognitive variables and alpha2 mean frequencies in the left hemisphere were independent of chronic heroin effects, whereas elevation of alpha2 frequency in the right hemisphere was strongly predicted by chronic heroin intake length. The patients with extremely high alpha2 mean frequency at the left central region were especially prone to failure in TLT due to the inability of the hypothesized alpha2-generating network, which normally projects to the central and temporal derivations bilaterally and to the right posterior temporal derivation to function appropriately. Hence, it was concluded that planning dysfunction in heroin abusers is related to alpha2 mean frequency shifts predominantly at the central regions
EEG spectral power and mean frequencies in early heroin abstinence
No full textThe purpose of the present study was to investigate cumulative heroin effects on brain functioning by studying relationships between EEG spectral power and mean frequencies and heroin abusing history. Eyes closed resting EEG data were collected from the 19 monopolar electrode sites in 33 heroin abusers and 13 age-matched healthy volunteers. The mean age of the patients was 23.1±4.5, the duration of daily heroin abuse (DDHA) ranged from 4 to 44 months, the i.v. doses of heroin ranged from 0.04 to 1.00 g/day, the abstinence length ranged from 6 days to 4.5 months. GLM repeated measures procedure revealed a significant group effect on the distribution of the mean power spectrum between bands and mean frequencies in almost all analyzed derivations. Further analysis demonstrated that these intergroup differences were diversely related to at least three aspects of heroin taking history. Frequency shifts in alpha2 range, most prominent in frontal and central derivations, were related to duration of daily heroin consumption. Slowing of alpha1 mean frequency, most prominent in central, temporal and occipital derivations, was registered mainly in heroin addicts who abused high doses of the drug. Spectral power characteristics of brain electrical activities in our patient population were strongly predicted by abstinence length. The present results give grounds to suppose that chronic heroin taking induces neuronal oscillation frequency changes, that may contribute to the development of antisocial trends and some semantic processes disturbances in these patients. Supplementary neurophysiological deficit is characteristic for heroin addicts, who takes high doses of the drug, however, its relation to heroin abusing remains unclear. Pronounced desynchronization is observed in acute heroin withdrawal, and spectral power characteristics tend to normalize almost completely during several weeks of abstinence
Single and combined effects of sympathetic and parasympathetic activity on perceptual sensitivity and attention
No full textPulse rate and cephalic pulse volume were recorded from 17 male and 37 female normal subjects during performance of an attentional task under high and low stress conditions. Verbal threshold (perceptual sensitivity) and word recognition (attention) were assessed using a visual verbal recognition task. Subjects were divided at the median for pulse rate and pulse volume during baseline, instruction, and task periods and grouped in terms of these two measures to represent different patterns of parasympathetic (vagal) and sympathetic activity. Analysis of variance was used to examine the effects of gender, stress condition, and autonomic pattern on autonomic activity, perceptual sensitivity, and attentional performance. Gender showed significant effects for pulse rate with higher scores for women during the instruction and task periods. High stress reduced perceptual sensitivity and resulted in better attentional performance. Whereas stress-induced sympathetic activity was related to low perceptual sensitivity and good attentional performance, high sympathetic in conjunction with low vagal baseline activity predicted relatively high perceptual sensitivity and poor attentional performance. Low or high baseline activity in both autonomic systems predicted low perceptual sensitivity and good attentional performance. Predictions of perception and attention can be improved by examining the effects of patterns of sympathetic and parasympathetic activity
Davydov soliton collisions
No full textIn this Letter, we study the collisions of Davydov solitons. The collision behaviour is diverse and complicated, and very sensitive to both the initial phases and velocities of the solitons. For some parameter ranges, Davydov solitons are stable to collisions in the sense that the solitons retain their structures, though for some cases, the propagation direction may be altered. For other parameter ranges, significant structural changes may occur: An exchange of energy between solitons, or the merger of two solitons to form a new bound state. (C) 1998 Elsevier Science B.V.Physics, MultidisciplinarySCI(E)8ARTICLE6282-28624
De vorming van wetenschappelijke begrippen: Davydov op de basisschool
No full textOnderstaand artikel geeft een overzicht van de begripsvormingstheorie van de sovjetpsycholoog V. V. Davydov. Davydov pleit voor het ontwikkelen van wetenschappelijke begrippen bij leerlingen. Dat zijn begrippen die ingekaderd zijn in een begrippenstelsel en hun betekenis volledig daaraan ontlenen. Van daaruit bekritiseert hij onderwijs dat via het principe van de aanschouwelijkheid begripsbetekenis wit funderen in waarnemingsgegevens. Vanuit zijn theorie legt Davydov de nadruk op de beweging van het abstracte (modellen) naar het concrete in het begripsvormingsproces en op de ontwikkeling van het algemene naar het bijzondere in het kader van het leerplan. Dit leren moet gebaseerd zijn op produktieve leeractiviteit van de leerlingen zelf, op het gebruik en de ontwikkeling van modellen en op cooperatie. Verder wijst Davydov ook steeds vaker op de ontwikkelingspsychologische voorwaarden voor het leren van wetenschappelijke begrippen. Davydovs theorie blijkt vruchtbaar voor onderwijs en onderzoek
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