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1.
2.
The effect of solar features on geospheric conditions leading to geomagnetic storms (GMSs) with planetary index,A
P ≥ 20 and the range of horizontal component of the Earth’s magnetic fieldH such that 250γ <H < 400γ has been investigated using interplanetary magnetic field (IMF), solar wind plasma (SWP) and solar geophysical data
(SGD) during the period 1978–99. Statistically, it is observed that maximum number of GMSs have occurred during the maximum
solar activity years of 21st and 22nd solar cycles. A peculiar result has been observed during the years 1982, 1994 when sunspot
numbers (SSNs) decrease very rapidly while numbers of GMSs increase. No distinct association between yearly occurrence of
disturbed days and SSNs is observed. Maximum number of disturbed days have occurred during spring and rainy seasons showing
a seasonal variation of disturbed days. No significant correlation between magnitude (intensity) of GMSs and importance ofH
α
, X-ray solar flares has been observed. Maximum number of GMSs is associated with solar flares of lower importance, i.e.,
SF during the period 1978-93.H
α
, X-ray solar flares occurred within lower helio-latitudes, i.e., (0–30)°N to (0–30)°S are associated with GMSs. NoH
α
, X-ray solar flares have occurred beyond 40°N or 40°S in association with GMSs. In helio-latitude range (10–40)°N to (10–40)°S,
the 89.5% concentration of active prominences and disappearing filaments (APDFs) are associated with GMSs. Maximum number
of GMSs are associated with solar flares. Coronal mass ejections (CMEs) are related with eruptive prominences, solar flares,
type IV radio burst and they occur at low helio-latitude. It is observed that CMEs related GMS events are not always associated
with high speed solar wind streams (HSSWSs). In many individual events, the travel time between the explosion on the Sun and
maximum activity lies between 58 and 118 h causing GMSs at the Earth. 相似文献
3.
High quality factor of dynamic structures at micro and nano scale is exploited in various applications of micro electro-mechanical
systems (MEMS) and nano electro-mechanical system. The quality factor of such devices can be very high in vacuum. However,
when vacuum is not desirable or not possible, the tiny structures must vibrate in air or some other gas at pressure levels
that may vary from atmospheric to low vacuum. The interaction of the surrounding fluid with the vibrating structure leads
to dissipation, thus bringing down the quality factor. Depending on the ambient fluid pressure or the gap between the vibrating
and the fixed structure, the fluid motion can range from continuum flow to molecular flow giving a wide range of dissipation.
The relevant fluid flow characteristics are determined by the Knudsen number which is the ratio of the mean free path of the
gas molecule to the characteristic flow length of the device. This number is very small for continuum flow and reasonably
big for molecular flow. In this paper, we study the effect of fluid pressure on the quality factor by carrying out experiments
on a MEMS device that consists of a double gimbaled torsional resonator. Such devices are commonly used in optical cross-connects
and switches. We only vary fluid pressure to make the Knudsen number go through the entire range of continuum flow, slip flow,
transition flow, and molecular flow. We experimentally determine the quality factor of the torsional resonator at different
air pressures ranging from 760 Torr to 0.001 Torr. The variation of this pressure over six orders of magnitude ensures required
rarefaction to range over all flow conditions. Finally, we get the variation of quality factor with pressure. The result indicates
that the quality factor, Q, follows a power law, Q ∝P
–r
, with different values of the exponent r in different flow regimes. In the second part of the paper, we propose the use of effective viscosity for considering velocity
slip conditions in solving Navier–Stokes equation numerically. This concept is validated with analytical results for a simple
case and then compared with the experimental results presented in this paper. The study shows that the effective viscosity
concept can be used effectively even for the molecular regime if the air-gap to length ratio is sufficiently small (h
0/L<0.01). As this ratio increases, the range of validity decreases. 相似文献
4.
Ramendra Pratap 《Tetrahedron letters》2007,48(15):2755-2759
A concise synthesis of highly functionalized 5,6-dihydrobenzo[h]quinoline-3-carbonitriles is delineated through base induced ring transformation of 4-sec-amino-2-oxo-5,6-dihydro-2H-benzo[h]chromene-3-carbonitriles with S-methylisothiourea sulfate and 1-carboxamidinepyrazole hydrochloride, separately, in DMF. Under analogous reaction conditions the ring transformation of 4-sec-amino-2-oxo-5,6-dihydro-2H-benzo[h]chromene-3-carbonitriles by formamidine acetate provided 4-sec-amino-benzo[h]quinoline-3-carbonitriles in moderate yields, while with benzamidine hydrochloride, the reaction followed the same mechanism to yield 2-phenyl-4-sec-amino-5,6-dihydrobenzo[h]quinoline-3-carbonitriles. 相似文献
5.
Ramendra Pratap 《Tetrahedron letters》2007,48(36):6318-6320
An easy and efficient synthesis of phenanthrene derivatives through base catalyzed ring transformation of 4-sec-amino-2-oxo-5,6-dihydro-2H-benzo[h]chromene-3-carbonitriles with acetyltrimethylsilane is described in good yields. The advantage of this reaction is the direct transformation of 2-oxobenzo[h]chromene into phenanthrene via C-C insertion from acetyltrimethylsilane. 相似文献
6.
Sudipta Jena Asit Ray Omprakash Mohanta Prabhat Kumar Das Ambika Sahoo Sanghamitra Nayak Pratap Chandra Panda 《Molecules (Basel, Switzerland)》2022,27(23)
Neocinnamomum caudatum (Lauraceae) plant is used in the traditional system of medicine and is considered a potential source of edible fruits, spices, flavoring agents and biodiesel. The leaves, bark and roots of the species are used by local communities for the treatment of inflammatory responses, such as allergies, sinusitis and urinary tract infections. However, there is no scientific evidence to support the molecular mechanism through which this plant exerts its anti-inflammatory effect. The aim of the current research was to characterize the chemical constituents of bark (NCB) and leaf (NCL) essential oil of N. caudatum and to elucidate its anti-inflammatory action in lipopolysaccharide (LPS)-treated RAW 264.7 cells. Essential oils extracted by hydrodistillation were further subjected to gas chromatography mass spectrometry (GC-MS) analysis. The major constituents in bark essential oil identified as β-pinene (13.11%), α-cadinol (11.18%) and α-pinene (10.99%), whereas leaf essential oil was found to be rich in β-pinene (45.21%), myrcene (9.97%) and α-pinene (9.27%). Treatment with NCB and NCL at a concentration of 25 µg/mL exerted significant anti-inflammatory activity by significantly reducing LPS-triggered nitric oxide (NO) production to 45.86% and 61.64%, respectively, compared to the LPS-treated group. In the LPS-treated group, the production of proinflammatory cytokines, such as tumor necrosis factor (TNF)-α, interleukin (IL)-6 and IL-1β, decreased after treatment with essential oil, alleviating the mRNA levels of inducible nitric oxide synthase (iNOS) and cyclooxygenase (COX)-2. The essential oil also inhibited the production of intracellular ROS and attenuated the depletion of mitochondrial membrane potential in a concentration-dependent manner. Pretreatment with NCB also reduced nuclear factor kappa-B (NF-κB)/p65 translocation and elevated the levels of endogenous antioxidant enzymes in LPS-induced macrophages. The present findings, for the first time, demonstrate the anti-inflammatory potential of both bark and leaf essential oils of N. caudatum. The bark essential oil exhibited a significantly more important anti-inflammatory effect than the leaf essential oil and could be used as a potential therapeutic agent for the treatment of inflammatory diseases. 相似文献
7.
A facile and short synthesis of 2-oxo-4-sec-amino-2,3,5,6-tetrahydrobenzo[f]isoquinoline-1-carbonitriles has been delineated through base catalyzed ring transformation of 5,6-dihydro-2-oxo-4-sec-amino-2H-benzo[h]chromene-3-carbonitrile by cyanoacetamide in excellent yields. 相似文献
8.
Dawn A Mukherjee P Nandi AK 《Langmuir : the ACS journal of surfaces and colloids》2007,23(10):5231-5237
The reducing property of an organically soluble conducting polymer (poly(o-methoxyaniline), POMA) is used to prepare monodisperse, size-controlled, highly populated, and highly stable silver nanoparticles in an organic medium through an interfacial redox process with an aqueous AgNO3 solution. The transition of emeraldine base (EB) to the pernigraniline base (PB) form of POMA occurs during nanoparticle formation, and the nitrogen atoms of POMA(PB) stabilize Ag nanoparticles by coordination to the adsorbed Ag(+) on the nanoparticle surface. The conductivity of the nanocomposite is on the order of 10(-11) S/cm, indicating that no doping of POMA occurs under the preparation conditions. The nanoparticles are free of excess oxidant and external stabilizer particles. The POMA (EB) concentration tailors the size of nanoparticles, and at its higher concentration (0.01% POMA with 0.01 N AgNO3), very dense Ag nanoparticles (6 x 10(15) particles/m(2)) of almost uniform size and shape are produced. The rate constant and Avrami exponent values of the nanoparticle formation are measured from the time-dependent UV-vis spectra using the Avrami equation. The Avrami exponent (n) values are close to 1, indicating 2D athermal nucleation with the circular shape of the nuclei having diffusion-controlled growth. The rate constant values are almost independent of AgNO3 concentration but are strongly dependent on POMA concentration. The higher rate constant with increasing POMA(EB) concentration has been attributed for the lowering of nanoparticle size due to increased nucleation density. 相似文献
9.
Jena Sudipta Ray Asit Sahoo Ambika Kamila Pradeep Kumar Nayak Sanghamitra Panda Pratap Chandra 《Chemistry of Natural Compounds》2021,57(6):1147-1149
Chemistry of Natural Compounds - 相似文献
10.
Dr. Greggory T. Kent Emily Morgan Kaitlin R. Albanese Dr. Anna Kallistova Dr. Alexandra Brumberg Linus Kautzsch Dr. Guang Wu Prof. Pratap Vishnoi Prof. Ram Seshadri Prof. Anthony K. Cheetham 《Angewandte Chemie (International ed. in English)》2023,62(32):e202306000
Halide double perovskites [A2MIMIIIX6] are an important class of materials that have garnered substantial interest as non-toxic alternatives to conventional lead iodide perovskites for optoelectronic applications. While numerous studies have examined chloride and bromide double perovskites, reports of iodide double perovskites are rare, and their definitive structural characterization has not been reported. Predictive models have aided us here in the synthesis and characterization of five iodide double perovskites of general formula Cs2NaLnI6 (Ln=Ce, Nd, Gd, Tb, Dy). The complete crystal structures, structural phase transitions, optical, photoluminescent, and magnetic properties of these compounds are reported. 相似文献