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1.
Upconversion phosphors are known as a material system that can convert near-infrared light into visible/ultraviolet emissions by sequentially absorbing multiple photons. The studies on upconversion materials often use two rare earth (RE) ions as a sensitizer-activator pair. We investigated the influences on luminescence intensity depending on Cr-doping content (x) of hexagonal NaLu0.98–xCrxF4Er0.02 (x = 0–0.9) upconversion material by substituting Lu3+ ions with Cr3+in the absence of Gd3+. The change in upconversion luminescence intensity appears with saddle-like shape. We suggest that Cr3+ ions play the dual role as a constituent in host lattice and a sensitizer in the upconversion process. Optimal conditions for gaining the strongest upconversion emission correspond to x = 0.3–0.5, where there are effective energy transfers between Cr3+ and Er3+ ions and CrEr dimers. Apart from these values, the emission intensity decreases rapidly which can be ascribed to the absence of multiple-photon absorption for the case of low Cr3+ contents, and to the coupling between Cr3+ and/or Er3+ ions for the case of high Cr3+ contents. Magnetization and electron-spin-resonant measurements were performed to understand the correlation between the optical and magnetic properties. 相似文献
2.
In this paper, a two-dimensional (2-D) method describing the whispering gallery mode in a microgear resonator is presented. The microgear is a microdisk surrounded by a circular grating. The method, which is based on the Floquet-Bloch formalism, analytically describes the field within the disk and outside the grating. On the other hand, the field within the grating is calculated using a finite-difference scheme in polar coordinates. Matching the boundary conditions, it is possible to work in a forced oscillation regime or in a free oscillation regime (laser mode). The resonant wavelength and quality factor can then be deduced. Compared to the coupled mode theory and to 2-D finite-difference time-domain computations, the method is faster and more accurate. Moreover, a polarization effect of the microgear is demonstrated. The TE polarization experiences a Q-factor improvement contrary to TM polarization. Finally, microgear structures prove to be more efficient than micro flowers. 相似文献
3.
DI Rodenhiser JD Andrews DN Mancini JH Jung SM Singh 《Canadian Metallurgical Quarterly》1997,373(2):185-195
Glutamatergic synaptic potentials induced by micromolar concentrations of the potassium conductance blocker 4-aminopyridine (4-AP) were recorded intracellularly from rat neostriatal neurons in the presence of 10 microM bicuculline (BIC). These synaptic potentials originate from neostriatal cortical and thalamic afferents and were completely blocked by 10 microM 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) plus 100 microM D-2-amino-5-phosphonovaleric acid (2-APV). Their inter-event time intervals could be fitted to exponential distributions, suggesting that they are induced randomly. Their amplitude distributions had most counts around 1 mV and fewer counts with values up to 5 mV. Since input resistance of the recorded neurons is about 40 M omega, the amplitudes agree to quantal size measurements in mammalian central neurons. The action of a D2 agonist, quinpirole, was studied on the frequency of these events. Mean amplitude of synaptic potentials was preserved in the presence of 2-10 microM quinpirole, but the frequency of 4-AP-induced glutamatergic synaptic potentials was reduced in 35% of cases. The effect was blocked by the D2 antagonist sulpiride (10 microM). Input resistance, membrane potential, or firing threshold did not change during quinpirole effect, suggesting a presynaptic site of action for quinpirole in some but not all glutamatergic afferents that make contact on a single cell. The present experiments show that dopaminergic presynaptic modulation of glutamatergic transmission in the neostriatum does not affect all stimulated afferents, suggesting that it is selective towards some of them. This may control the quality and quantity of afferent flow upon neostriatal neurons. 相似文献
4.
In anesthetized intact rats, cerebral blood flow is autoregulated until mean arterial blood pressure (MAP) exceeds 150 mmHg. At higher pressures cerebral blood flow breaks through autoregulation and rapidly increases. However, interruption of the arterial baroreceptor reflex eliminates breakthrough of autoregulation. Thus, breakthrough may reflect active rather than passive vasodilatation. We, therefore, sought to determine if breakthrough depends upon synthesis of the vasodilator nitric oxide. Thirty-eight anesthetized adult male Sprague-Dawley rats were studied. In all, MAP was raised by slow i.v. infusion of phenylephrine. In rats pretreated with the nitric oxide synthase inhibitor L-nitroarginine (L-NA; 22 mg/kg i.v.) or with a combination of L-NA plus D-arginine (D-Arg; 240 mg/kg i.v.), breakthrough did not occur even when MAP exceeded 185 mmHg (L-NA) and 165 mmHg (D-Arg). In contrast, breakthrough occurred in rats treated with L-NA plus L-arginine (L-Arg; 240 mg/kg i.v.) and in rats whose basal vascular tone had been increased by pretreatment with arginine vasopressin prior to infusion of phenylephrine. Removal of sympathetic innervation to cerebral vessels attenuated, but did not eliminate, effects of L-NA on breakthrough. Thus, vasodilatation seen with breakthrough of autoregulation depends upon release of nitric oxide or a nitric oxide donor. 相似文献
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Cattle feedlot dust is an annoyance and may be a route for nutrient transport, odor emission, and pathogen dispersion, but important environmental factors that contribute to dust emissions are poorly characterized. A general protocol was devised to test feedlot samples for their ability to produce dust under a variety of environmental conditions. A blender was modified to produce dust from a variety of dried feedlot surface and soil samples and collect airborne particles on glass fiber filters by vacuum collection. A general blending protocol optimized for sample volume (150-175 cm3), blending time (5 min of pre-blending), and dust collection time (15 s) provided consistent dust measurements for all samples tested. The procedure performed well on samples that varied in organic matter content, but was restricted to samples containing less than 200 to 700 g H2O kg(-1) dry matter (DM). When applied to field samples, the technique demonstrated considerable spatial variability between feedlot pen sites. Mechanistically, dust potential was related to moisture and organic matter content. An alternative protocol also demonstrated differences within pen sites in maximum dust potential and dust airborne residence time. The two protocols were not intended, nor are they suitable, for predicting actual particulate matter emissions from agricultural sources. Rather, the protocols rapidly and inexpensively compared the potential for dust emission from samples of differing composition under a variety of environmental conditions. 相似文献
9.
KC Wolthers SA Otto SM Lens DN Kolbach RA van Lier F Miedema L Meyaard 《Canadian Metallurgical Quarterly》1996,26(8):1700-1706
T cells express CD28 and CD27 which transduce co-stimulatory signals after interaction with their ligands on antigen-presenting cells (APC). These ligands, CD80, CD86 and CD70, are also expressed to some extent on activated T cells. Here, we show that in human immunodeficiency virus (HIV)-infected individuals, CD28 and CD27 expression is decreased on CD8+ T cells. On the other hand, T cell stimulation in vitro induced high CD80, CD86 and CD70 expression on T cells from HIV-infected individuals. It appeared that an inverted CD4:CD8 T cell ratio could explain this enhanced expression of co-stimulatory ligands. Indeed, high expression levels of CD80, CD86 and CD70 were found on activated CD8+ T cells from HIV- individuals cultured in the absence of CD4+ T cells. Addition of CD4+ T cells prevented this up-regulation. However, in HIV-infected individuals, addition of excess autologous or healthy control CD4+ T cells did not completely counteract up-regulation of co-stimulatory ligand expression on CD8+ T cells. Thus, to some extent, CD8+ T cells in HIV-infected individuals appeared to be refractory to CD4+ T cell-mediated regulation of ligand expression in vitro. Activated T cells from HIV-infected individuals and activated CD8+ T cells from healthy controls were able to act as accessory cells in CD3-induced T cell proliferation, which was dependent on cell-cell contact. Thus, we showed that T cells from HIV-infected individuals express enhanced levels of co-stimulatory ligands upon activation, which provides them with accessory cell properties. Enhanced stimulatory potential of these nonprofessional APC may contribute to persistently high levels of immune activation in HIV infection related to disease progression. 相似文献
10.
SH Thomas JE Horner K Chew J Connolly B Dorani L Bevan S Bhattacharyya MG Bramble KH Han A Rodgers B Sen B Tesfayohannes H Wynne DN Bateman 《Canadian Metallurgical Quarterly》1997,16(9):495-500
1. Paracetamol is increasingly involved in self-poisoning in the United Kingdom and remains a common cause of fatal poisoning. 2. To document the epidemiology and early management of paracetamol poisoning data were collected on consecutive patients with suspected paracetamol poisoning presenting to 6 hospitals in the North East of England over 12 weeks in 1994. 3. There were 400 presentations (attendance rate 1.14/10(3) population/yr) involving 343 persons (45% male). Paracetamol concentrations at 4 h correlated weakly with reported paracetamol dose (R = 0.49, P < 0.0001) and were similar comparing those treated and not treated by gastric decontamination. 4. In 38 (9%) cases paracetamol concentrations were above the appropriate nomogram treatment line, including 3% and 20% of patients who reported ingesting less than and more than 12 g respectively. In 21 patients acetylcysteine treatment was deferred until admission to the ward, the mean delay involved was 2.8 h. 5. One patient died, from arrhythmias caused by co-ingested dothiepin. 6. Paracetamol poisoning is common. Most cases do not have potentially toxic plasma paracetamol concentrations, but those who do often present late and antidotal treatment may be delayed inappropriately. 相似文献