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.     

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.     

HIV infection and AIDS

The entry of one HIV virion into a human being has the potential to cause death by the inexorable replication of the virus within the principal T lymphocyte, the CD4+ T cell. Although combination antiretroviral therapy, particularly therapy with protease inhibitors, decreases the viral burden to very low, even undetectable, levels, sequestration of the virus in privileged sites, including a long-lived CD4+ T cell, has frustrated efforts at eradication of HIV. Activation of the immune system, therefore, appears essential before this infection can be conquered. Powerful vaccines capable of preventing infection remain the hope of the world.     

Wave-front curvature as a cause of slow conduction and block in isolated cardiac muscle

We have investigated the role of wave-front curvature on propagation by following the wave front that was diffracted through a narrow isthmus created in a two-dimensional ionic model (Luo-Rudy) of ventricular muscle and in a thin (0.5-mm) sheet of sheep ventricular epicardial muscle. The electrical activity in the experimental preparations was imaged by using a high-resolution video camera that monitored the changes in fluorescence of the potentiometric dye di-4-ANEPPS on the surface of the tissue. Isthmuses were created both parallel and perpendicular to the fiber orientation. In both numerical and biological experiments, when a planar wave front reached the isthmus, it was diffracted to an elliptical wave front whose pronounced curvature was very similar to that of a wave front initiated by point stimulation. In addition, the velocity of propagation was reduced in relation to that of the original planar wave. Furthermore, as shown by the numerical results, wave-front curvature changed as a function of the distance from the isthmus. Such changes in local curvature were accompanied by corresponding changes in velocity of propagation. In the model, the critical isthmus width was 200 microns for longitudinal propagation and 600 microns for transverse propagation of a single planar wave initiated proximal to the isthmus. In the experiments, propagation depended on the width of the isthmus for a fixed stimulation frequency. Propagation through an isthmus of fixed width was rate dependent both along and across fibers. Thus, the critical isthmus width for propagation was estimated in both directions for different frequencies of stimulation. In the longitudinal direction, for cycle lengths between 200 and 500 milliseconds, the critical width was < 1 mm; for 150 milliseconds, it was estimated to be between 1.3 and 2 mm; and for the maximum frequency of stimulation (117 +/- 15 milliseconds), it was > 2.5 mm. In the transverse direction, critical width was between 1.78 and 2.32 mm for a basic cycle length of 200 milliseconds. It increased to values between 2.46 and 3.53 mm for a basic cycle length of 150 milliseconds. The overall results demonstrate that the curvature of the wave front plays an important role in propagation in two-dimensional cardiac muscle and that changes in curvature may cause slow conduction or block.     

Preweaning growth traits for Senepol, Hereford, and reciprocal crossbred calves and feedlot performance and carcass characteristics of steers

We conducted a multiyear study in two phases to determine preweaning performance traits of Senepol (S x S), Hereford (H x H), and reciprocal (S x H and H x S) F1 crossbred calves and feedlot performance and carcass characteristics of steers. In Phase I, from 1985 to 1989, data from S x S (n = 194), H x H (n = 383), and S x H (n = 120) calves were used. Numbers of S x S cows were increased during Phase I so that data from H x S (n = 74) calves could be included in Phase II (1990 to 1992) in addition to S x S (n = 118), H x H (n = 130), and S x H (n = 56) calves. Also during Phase II, feedlot performance and carcass characteristics were determined for S x S (n = 30), H x H (n = 26), H x S (n = 36), and S x H (n = 26) steers. In Phase I, S x S calves had heavier (P < .01) birth weights and heavier (P < .01) 205-d adjusted weaning weights than H x H calves. Birth weights of S x H calves were heavier (P < .01) than the mean of the purebred calves, but 205-d adjusted weaning weights did not differ (P > .10). In phase II, direct heterosis was 3.5% for birth weight (P < .05) and 5.1% for 205-d adjusted weaning weight (P < .01). Senepol maternal breed effects were 1.9 kg for birth weight (P < .10) and 37.9 kg for 205-d adjusted weaning weight (P < .01). Levels of direct heterosis, Senepol maternal breed effects, and Hereford direct breed effects were significant for most feedlot performance traits of steer calves that were fed to a common end point. Breeds did not differ (P > .10) for USDA yield and quality grades, and direct heterosis was not significant for Warner-Bratzler shear force. These results demonstrate significant levels of heterosis in preweaning performance between S x S and H x H calves and in feedlot performance of steers. Levels of heterosis were smaller and nonsignificant for most carcass traits including meat tenderness, which did not differ between S x S and H x H steers in this study.