欧洲主要电信运营商专线资费的演变

欧洲主要电信运营商所处国度的经济和人口布局情况不同，竞争环境也有差别，在专线资费方面的做法也有许多不同之处。考虑到地区之间竞争的差异。目前多数国家都取消了地区交叉补贴的做法，但还有一部分国家仍然坚持统一费率。在资费方面的基本促销手段为接合同年限和用户的支出额打折。从2000年到2003年资费演变的基本情况是；接入费扣2Mbit／s以下较低速率的专线租费保持平稳略有下降，较高速率专线的租费则有较大的下调幅虚。     

Animal-induced injuries and disease, neonatal jaundice, immunizations, and viral infections

Highlights from the past years' literature on the topics of animal-induced injuries and diseases, neonatal jaundice, immunizations, and viral infections are discussed from the perspective of the general pediatrician. An effort is made to place recent advances in care or understanding of clinical problems into the context of the pediatric office practice. The current reality of health care-be it managed care, care for the underserved, or the recent pressures on academic and hospital-based medicine-does not alter the importance of the delivery of quality care at the office level. Although it is now popular to define quality of health care in cute advertising copy, as if we are selling durable goods, excellence in pediatric office-based practice continues to require broad strokes of medical knowledge coupled with a unswerving commitment to and advocacy for the needs and well-being of infants, children, and young adults.     

Peripheral nerve stimulation in a whole-body echo-planar imaging system

Echo-planar techniques in MRI use a rapidly oscillating frequency-encoding gradient with the potential to produce peripheral nerve stimulation. To evaluate the incidence, type, and location of stimulation in a commercial whole-body scanner, we studied two groups: (a) 173 consecutive individuals scanned by echo-planar imaging for other purposes and (b) seven subjects who were scanned with an extensive set of 36 echo-planar sequences (with prompting after each scan to report any peripheral nerve stimulation) to test the effects of various parameters. Although only 5% of group A reported symptoms of peripheral nerve stimulation, all in group B experienced some type of stimulation, dependent primarily on direction of the oscillating gradient and location of the body within the gradient coil. Maximum stimulation typically occurred 30 to 40 cm from isocenter in the region of maximum dB/dt. Generally, y gradients produced truncal stimulation, and x gradients produced stimulation in the head. When hands were clasped over the abdomen, a tingling in the hands occasionally was felt. Patients should be instructed to keep their hands apart.     

An assessment of potential nonlinear circuit models for thecharacterization of resonant tunneling diodes

The intrinsically fast process of resonant tunneling through double barrier heterostructures along with the existence of negative differential resistance in the current-voltage characteristic of these structures has led to their implementation as sources for high frequency electromagnetic energy. While sources based upon resonant tunneling diodes (RTDs) have produced frequency of oscillations up to 712 GHz, only microwatt levels of performance has been achieved above 100 GHz. Since stability criteria plays critical role in determining the deliverable power of any oscillator, a physically accurate equivalent-circuit model for the RTD is extremely important for optimizing the dynamics of the device-cavity package. This study identifies a distinctly new equivalent circuit model for characterizing the modes of oscillation in RTD-based sources. Specifically, in order to exhibit the fundamental self-oscillations and the overall I-V characteristics (plateau structure and hysteresis) observed experimentally, an accurate circuit model of the RTD must incorporate: (i) a quantum-well inductance which directly chokes the nonlinear conductance and, (ii) a nonlinear access resistance, associated with the accumulation of charge in the injection region of the double barriers, with a nonlocal dependence on the bias across the double barrier structure     

Abnormal mucosal glycoprotein synthesis in inflammatory bowel diseases is not related to cigarette smoking

Patients with ulcerative colitis are usually non- or ex-smokers in contrast to Crohn's disease where smoking is common. Abnormalities of quantity and quality of intestinal mucus have been postulated in the pathogenesis of these diseases. It is possible that smoking habit may exert its effects via changes in mucus in inflammatory bowel disease. We have therefore studied incorporation of N-acetylglucosamine into synthesized colonic mucin in explants from 85 controls with normal colonoscopic appearances and histology, including 27 smokers and 58 nonsmokers, 36 patients with ulcerative colitis and 19 with ileocolonic Crohn's disease over 24 h in tissue culture. Incorporation of N-acetylglucosamine into normal explants was 31.3 +/- (SD) 7.1 dpm/microgram biopsy protein, incorporation was increased in patients with active Crohn's disease (mean 41.2 +/- (SD) 10.4 dpm/microgram biopsy protein, p = 0.003), decreased in inactive ulcerative colitis (mean 24.1 +/- 7.8 dpm/microgram biopsy protein, p = 0.0006) but normal in active ulcerative colitis (mean 35.0 +/- 13.8 dpm/microgram biopsy protein, p = 0.44). No significant relationship was found between cigarette smoking habits and mucus synthesis in controls with normal mucosa (nonsmokers, n = 58, mean 31.0 +/- (SD) 7.52 dpm/microgram biopsy protein; smokers, n = 27, mean 31.8 +/- (SD) 6.1 dpm/microgram biopsy protein, p = 0.9). This study shows that mucus glycoprotein synthesis is reduced in inactive ulcerative colitis, rising to normal levels in active disease and that synthesis is increased in Crohn's disease. There is no effect of smoking on mucus synthesis by control biopsies suggesting that the differences seen in inflammatory bowel disease are not related to cigarette smoking.     

Inhibition of nitric oxide synthesis extends cerebrovascular autoregulation during hypertension

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.     

Phenotypic diversity and kinetics of proliferating microglia and astrocytes following cortical stab wounds

Brain injury induces reactive gliosis, characterized by increased expression of glial fibrillary acidic protein (GFAP), astrocyte hypertrophy, and hyperplasia of astrocytes and microglia. One hypothesis tested in this study was whether ganglioside GD3+ glial precursor cells would contribute to macroglial proliferation following injury. Adult rats received a cortical stab wound. Proliferating cells were identified by immunostaining for proliferating cell nuclear antigen (PCNA) and by [3H]-thymidine autoradiography, and cell phenotypes by immunocytochemical staining for GD3, GFAP, ED1 (for reactive microglia) and for Bandeiraea Simplicifolia isolectin-B4 binding (all microglia). Animals were labeled with thymidine at 1,2,3, and 4 days postlesion (dpl) and sacrificed at various times thereafter. Proliferating cells of each phenotype were quantified. A dramatic upregulation of GD3 on ramified microglia was seen in the ipsilateral hemisphere by 2 dpl. Proliferating cells consisted of microglia and fewer astrocytes. Microglia proliferated maximally at 2-3 dpl and one third to one half were GD3+. Astrocytes proliferated maximally at 3-4 dpl, and some were also GD3+. Both ramified and ameboid forms of microglia proliferated and by 4 dpl all GD3+ microglia were ED1+ and vice versa. In the contralateral cortex microglia expressed neither GD3 nor ED1. Thus they acquired these antigens when activated. Neither microglia nor astrocytes that were thymidine-labeled at 2, 3, or 4 dpl changed in number in subsequent days. Most thymidine+ astrocytes were large GFAP+ reactive cells that clearly arose from pre-existing astrocytes, not from GD3+ glial precursors. In this model of injury microglia proliferate earlier and to a much greater extent than astrocytes, they can divide when in ramified form, and GD3 is up-regulated in most reactive microglia and in a subset of reactive astrocytes. We also conclude that microglial proliferation precedes proliferation of invading blood-borne macrophages.     

Reprocessing of Microcrystalline Cellulose Spheres with Low Drug Concentrations

Spherical dosage forms have been reported to be an efficient and effective method for delivering drugs into the body and controlling their dissolution rate. Substantial work has been conducted in these laboratories illustrating the advantages of microcrystalline cellulose-based spheres for these purposes. Through various methodologies, but most routinely the extrusion and marumerization technique, it has been determined by Funck, et al. that not more than 50% drug can be incorporated into a sphere formulation without the addition of other binders.

Because of the nature of the extrusion and marumerization manufacturing process, the type of drug being processed and the resultant particle size requirements of the spheres, the percent of spheres falling outside the desired particle size can range from between 3% and 20%. For this reason and the possibility of operator errors, our objective was to determine the parameters which needed monitoring when reprocessing was necessary.