网络存储的发展历程及新兴的iSCSI

目前SAN和NAS存储正在迅速发展，DAS的生存空间越来越小。今天超过1／3的存储是网络化的，如果不是因为FC的高成本和复杂性．这个数字还会更大。iSCSI是IETF一种新的标准协议．它将SCSI命令压缩到TCP／IP包．使数据块在IP网络上传播。和FC-SAN相比．高速千兆iSCSI耙SCSI、以太网和TCP／IP结合起来，具有许多优势．如建立在稳定和熟悉的标准上；较低的总拥有成本，安装和维修费用很低；较高程度的可操作性，减少了异构网络和电缆．使用一般的以太网交换机而不是特殊的FC交换机；等等。     

Evaluation of the humoral immune response of CD rats following a 2-week exposure to the pesticide carbaryl by the oral, dermal, or inhalation routes

The objective of this study was to examine the immunotoxicological effects of the methyl-carbamate pesticide carbaryl via the oral, dermal, or inhalation routes. Male CD rats were exposed to carbaryl 5 d/wk for a 2-wk period. During nose-only inhalation exposures, rats received either 36, 137, or 335 mg/m3 carbaryl in acetone for 6 h. Air only and acetone/air controls were run concurrently. Orally exposed animals received either 1 ml corn oil or 10, 25, or 50 mg/kg carbaryl, while dermally exposed animals received either 2 ml acetone or 100, 500, or 1000 mg/kg carbaryl on their dorsal flank for 6 h. Four days prior to sacrifice, animals from all exposure groups were injected iv with 2 x 10(8) sheep red blood cells (SRBC). The primary immunoglobulin M (IgM) humoral immune response to SRBC was then assessed by measuring SRBC-specific antibody-forming cells (AFC) and levels of serum anti-SRBC IgM antibody, respectively, using the hemolytic plaque assay and an enzyme-linked immunosorbent assay. Individual body weights, spleen, thymus, and liver weights, spleen cell number, and red and white blood cell (RBC, WBC) counts were obtained for each animal. Following nose-only inhalation exposures, dose-dependent decreases in thymus weights, spleen cell number, AFC/spleen, AFC/10(6) splenocytes, and serum levels of SRBC-specific IgM antibody were observed. Significant decreases of 33, 57, and 22% in spleen cell number, AFC/spleen, and thymus weight, respectively, were found at the 335 mg/m3 exposure level. Animals exposed orally to 25 mg/kg carbaryl had a 34% decrease in WBC counts. A 34% decrease in WBC and a 13% increase in RBC counts were observed at the 50 mg/kg oral dose. Significant decreases in liver weights ranging from 11 to 13% were found at all oral exposure levels. Dermal exposure to carbaryl revealed no significant toxicological effects. Results indicate that humoral immune suppression was observed following inhalation, but not following oral or dermal exposures to carbaryl. Immunotoxicological studies evaluating pesticides need to consider relevant exposure routes and dosages for appropriate risk assessment procedures and exposure limits to be established.     

Frequency-dependence of myocardial energetics in failing human myocardium as quantified by a new method for the measurement of oxygen consumption in muscle strip preparations

Diastolic dysfunction at high heart rates may be associated with increased myocardial energy consumption. Frequency-dependent changes of isometric force and oxygen consumption (MVO2) were investigated in strip preparations from endstage failing human hearts exhibiting various degrees of diastolic dysfunction. MVO2 was determined by a new method which was validated. When stimulation rate was increased from 40 to 200 min-1 (n=7), developed force decreased from 16.5+/-4.3 to 7.9+/-2.9 mN/mm2 (P<0.01), diastolic force increased from 15.9+/-3.2 to 22.0+/-3.0 mN/mm2 (P<0.01), and total MVO2 increased from 2.6+/-0.6 to 4.7+/-0.9 ml/min/100 g (P<0.025). Resting MVO2 and resting force were 1.8+/-0.4 ml/min/100 g and 15.9+/-3.0 mN/mm2, respectively. After addition of 30 mm 2,3-butanedione monoxime (BDM) to inhibit crossbridges, resting MVO2 and resting force decreased by 46% (P<0.05) and 15% (P<0.01), respectively, indicating the presence of active force generation in unstimulated failing human myocardium. In each muscle preparation, there was a significant correlation between force-time integral (FTI) and total MVO2 (r=0.96+/-0.01). The strength of these correlations did not vary with the contribution of diastolic FTI to total FTI. The ratio of activity related MVO2 to developed FTI, an inverse index of the economy of contraction, increased depending on the rise of diastolic FTI at higher stimulation rates. In conclusion, in failing human myocardium, diastolic force development is occurring at the same energy expenditure as systolic force generation. Therefore, in muscle preparations with disturbed diastolic function economy of contraction decreases with higher stimulation rates, depending on the rise of diastolic force.     

Determination of the viremia threshold for dental cross-infection in a mouse model

An animal model of dental virus transmission was developed using the lactate dehydrogenase-elevating virus (LDV) of mice to study cross infection. Mouse-to-mouse cross-infection was carried out by scaling the teeth of LDV-infected donor mice with dental instruments, immediately prior to using the contaminated instruments on the teeth of recipient indicator mice. The level of donor viremia was found to correlate with the rate of virus cross-infection, with a viremia threshold level of 10(7.5) ID50/ml observed for dental cross-infection. The blood volume transferred during dental cross-infection was approximately 10(-4) to 10(-5) ml, demonstrating the inefficiency of virus cross-infection, since deposition of about 1000 virions on dental instruments was associated with the threshold limit. Virus transferred during dental cross-infection rapidly entered the blood circulation, showing that dental cross-infection was not dependent on an oral infection. The results from these model studies predict the general inefficiency of dental instrument virus cross-infection, and a further reduced likelihood of dental cross-infection with appropriately cleaned instruments.     

Electrostatic activation of Escherichia coli methionine repressor

BACKGROUND: The three-dimensional structure of the Escherichia coli methionine repressor (met repressor) is relatively unperturbed by the binding of its corepressor, S-adenosylmethionine (SAM), and of operator DNA. The positively charged corepressor binds to sites on the repressor remote from the DNA-binding site, and despite the lack of induced structural change is able to raise the affinity for operator DNA by a factor of up to 1000. Neutral corepressor analogues also bind to the repressor, but do not increase operator affinity. These observations suggest that the corepressor effect may be electrostatic. RESULTS: Using the program DELPHI, we have calculated electrostatic potentials for the repressor and its complexes, and have obtained results consistent with an electrostatic model for repressor activation. The positive potential originating from the corepressor is propagated through the repressor-operator complex, and is significant at DNA phosphate groups buried in the protein-DNA interface. The rank order of calculated electrostatic interaction energies for complexes with SAM, and two closely-related analogues, is in agreement with experimental measurements of the corresponding repressor-operator affinities. CONCLUSION: Long-range (> 10 A) electrostatic interactions between bound corepressor and operator phosphate groups in the repressor-operator complex may be sufficient to explain repressor activation Met repressor could, therefore, be an electrostatically triggered genetic switch.