Although there is tremendous interest in designing improved networks for data centers, very little is known about the network-level traffic characteristics of data centers today. In this paper, we conduct an empirical study of the network traffic in 10 data centers belonging to three different categories, including university, enterprise campus, and cloud data centers. Our definition of cloud data centers includes not only data centers employed by large online service providers offering Internet-facing applications but also data centers used to host data-intensive (MapReduce style) applications). We collect and analyze SNMP statistics, topology and packet-level traces. We examine the range of applications deployed in these data centers and their placement, the flow-level and packet-level transmission properties of these applications, and their impact on network and link utilizations, congestion and packet drops. We describe the implications of the observed traffic patterns for data center internal traffic engineering as well as for recently proposed architectures for data center networks.
The fluorescence of individual nitrogen-vacancy defect centers in diamond was observed with room-temperature scanning confocal optical microscopy. The centers were photostable, showing no detectable change in their fluorescence emission spectrum as a function of time. Magnetic resonance on single centers at room temperature was shown to be feasible. The magnetic resonance spectra revealed marked changes in zero-field splitting parameters among different centers. These changes were attributed to strain-induced differences in the symmetry of the centers.
We present the impact tests that preceded the most recent operational upgrades to the land surface model used in the National Centers for Environmental Prediction (NCEP) mesoscale Eta model, whose operational domain includes North America. These improvements consist of changes to the “Noah” land surface model (LSM) physics, most notable in the area of cold season processes. Results indicate improved performance in forecasting low‐level temperature and humidity, with improvements to (or without affecting) the overall performance of the Eta model quantitative precipitation scores and upper air verification statistics. Remaining issues that directly affect the Noah LSM performance in the Eta model include physical parameterizations of radiation and clouds, which affect the amount of available energy at the surface, and stable boundary layer and surface layer processes, which affect surface turbulent heat fluxes and ultimately the surface energy budget.
OBJECTIVE: To present a clinical version of the 2000 Centers for Disease Control and Prevention (CDC) growth charts and to compare them with the previous version, the 1977 National Center for Health Statistics (NCHS) growth charts. METHODS: The 2000 CDC percentile curves were developed in 2 stages. In the first stage, the empirical percentiles were smoothed by a variety of parametric and nonparametric procedures. To obtain corresponding percentiles and z scores, we approximated the smoothed percentiles using a modified LMS estimation procedure in the second stage. The charts include of a set of curves for infants, birth to 36 months of age, and a set for children and adolescents, 2 to 20 years of age. RESULTS: The charts represent a cross-section of children who live in the United States; breastfed infants are represented on the basis of their distribution in the US population. The 2000 CDC growth charts more closely match the national distribution of birth weights than did the 1977 NCHS growth charts, and the disjunction between weight-for-length and weight-for-stature or length-for-age and stature-for-age found in the 1977 charts has been corrected. Moreover, the 2000 CDC growth charts can be used to obtain both percentiles and z scores. Finally, body mass index-for-age charts are available for children and adolescents 2 to 20 years of age. CONCLUSION: The 2000 CDC growth charts are recommended for use in the United States. Pediatric clinics should make the transition from the 1977 NCHS to the 2000 CDC charts for routine monitoring of growth in infants, children, and adolescents.
The findings and conclusions in this report are those of the authors and do not necessarily represent the views of the Centers for Disease Control and Prevention.
Germinal centers (GCs) were described more than 125 years ago as compartments within secondary lymphoid organs that contained mitotic cells. Since then, it has become clear that this structure is the site of B cell clonal expansion, somatic hypermutation, and affinity-based selection, the combination of which results in the production of high-affinity antibodies. Decades of anatomical and functional studies have led to an overall model of how the GC reaction and affinity-based selection operate. More recently, the introduction of intravital imaging into the GC field has opened the door to direct investigation of certain key dynamic features of this microanatomic structure, sparking renewed interest in the relationship between cell movement and affinity maturation. We review these and other recent advances in our understanding of GCs, focusing on cellular dynamics and on the mechanism of selection of high-affinity B cells.
Objectives. We evaluated whether the decline of the racial disparity in preterm birth during the last decade was commensurate with a decline in the contribution of preterm birth to the infant mortality gap. Methods. We used linked files of 1990 and 2000 data on US infant births and deaths to partition the gap between Black and White infant mortality rates into differences in the (1) distribution of gestational age and (2) gestational age–spe-cific mortality rates. Results. Between 1990 and 2000, the Black–White infant mortality rate ratio did not change significantly (2.3 vs 2.4). Excess deaths among preterm Black in-fants accounted for nearly 80 % of the Black–White infant mortality gap in both 1990 and 2000. The narrowing racial disparity in the preterm birth rate was coun-terbalanced by greater mortality reductions in White than in Black preterm in-fants. Extremely preterm birth (<28 weeks) was 4 times higher in Black infants and accounted for more than half of the infant mortality gap. Conclusions. Substantial reductions in the Black–White infant mortality gap will require improved prevention of extremely preterm birth among Black in-
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The concepts of the “center” and the “median vertex” of a graph are generalized to the “absolute center” and the “absolute median” of a weighted graph (a graph with weights attached to its vertices as well as to its branches). These results are used to find the optimum location of a “switching center” in a communication network and to locate the best place to build a “police station” in a highway system. It is shown that the optimum location of a switching center is always at a vertex of the communication network while the best location for the police station is not necessarily at an intersection. Procedures for finding these locations are given.
OBJECTIVE: To encourage increased participation in physical activity among Americans of all ages by issuing a public health recommendation on the types and amounts of physical activity needed for health promotion and disease prevention. PARTICIPANTS: A planning committee of five scientists was established by the Centers for Disease Control and Prevention and the American College of Sports Medicine to organize a workshop. This committee selected 15 other workshop discussants on the basis of their research expertise in issues related to the health implications of physical activity. Several relevant professional or scientific organizations and federal agencies also were represented. EVIDENCE: The panel of experts reviewed the pertinent physiological, epidemiologic, and clinical evidence, including primary research articles and recent review articles. CONSENSUS PROCESS: Major issues related to physical activity and health were outlined, and selected members of the expert panel drafted sections of the paper from this outline. A draft manuscript was prepared by the planning committee and circulated to the full panel in advance of the 2-day workshop. During the workshop, each section of the manuscript was reviewed by the expert panel. Primary attention was given to achieving group consensus concerning the recommended types and amounts of physical activity. A concise "public health message" was developed to express the recommendations of the panel. During the ensuing months, the consensus statement was further reviewed and revised and was formally endorsed by both the Centers for Disease Control and Prevention and the American College of Sports Medicine. CONCLUSION: Every US adult should accumulate 30 minutes or more of moderate-intensity physical activity on most, preferably all, days of the week.
We construct dynamical models for a sample of 36 nearby galaxies with Hubble Space Telescope (HST) photometry and ground-based kinematics. The models assume that each galaxy is axisymmetric, with a two-integral distribution function, arbitrary inclination angle, a position-independent stellar mass-to-light ratio Y, and a central massive dark object (MDO) of arbitrary mass M•. They provide acceptable fits to 32 of the galaxies for some value of M• and Y; the four galaxies that cannot be fitted have kinematically decoupled cores. The mass-to-light ratios inferred for the 32 well-fitted galaxies are consistent with the fundamental-plane correlation Y ∝ L0.2, where L is galaxy luminosity. In all but six galaxies the models require at the 95% confidence level an MDO of mass M• ∼ 0.006Mbulge ≡ 0.006YL. Five of the six galaxies consistent with M• = 0 are also consistent with this correlation. The other (NGC 7332) has a much stronger upper limit on M•. We predict the second-moment profiles that should be observed at HST resolution for the 32 galaxies that our models describe well. We consider various parameterizations for the probability distribution describing the correlation of the masses of these MDOs with other galaxy properties. One of the best models can be summarized thus: a fraction f ≃ 0.97 of early-type galaxies have MDOs, whose masses are well described by a Gaussian distribution in log (M•/Mbulge) of mean -2.28 and standard deviation ∼0.51. There is also marginal evidence that M• is distributed differently for "core" and "power law" galaxies, with core galaxies having a somewhat steeper dependence on Mbulge.
IMPORTANCE: The human and financial costs of treating surgical site infections (SSIs) are increasing. The number of surgical procedures performed in the United States continues to rise, and surgical patients are initially seen with increasingly complex comorbidities. It is estimated that approximately half of SSIs are deemed preventable using evidence-based strategies. OBJECTIVE: To provide new and updated evidence-based recommendations for the prevention of SSI. EVIDENCE REVIEW: A targeted systematic review of the literature was conducted in MEDLINE, EMBASE, CINAHL, and the Cochrane Library from 1998 through April 2014. A modified Grading of Recommendations, Assessment, Development, and Evaluation (GRADE) approach was used to assess the quality of evidence and the strength of the resulting recommendation and to provide explicit links between them. Of 5759 titles and abstracts screened, 896 underwent full-text review by 2 independent reviewers. After exclusions, 170 studies were extracted into evidence tables, appraised, and synthesized. FINDINGS: Before surgery, patients should shower or bathe (full body) with soap (antimicrobial or nonantimicrobial) or an antiseptic agent on at least the night before the operative day. Antimicrobial prophylaxis should be administered only when indicated based on published clinical practice guidelines and timed such that a bactericidal concentration of the agents is established in the serum and tissues when the incision is made. In cesarean section procedures, antimicrobial prophylaxis should be administered before skin incision. Skin preparation in the operating room should be performed using an alcohol-based agent unless contraindicated. For clean and clean-contaminated procedures, additional prophylactic antimicrobial agent doses should not be administered after the surgical incision is closed in the operating room, even in the presence of a drain. Topical antimicrobial agents should not be applied to the surgical incision. During surgery, glycemic control should be implemented using blood glucose target levels less than 200 mg/dL, and normothermia should be maintained in all patients. Increased fraction of inspired oxygen should be administered during surgery and after extubation in the immediate postoperative period for patients with normal pulmonary function undergoing general anesthesia with endotracheal intubation. Transfusion of blood products should not be withheld from surgical patients as a means to prevent SSI. CONCLUSIONS AND RELEVANCE: This guideline is intended to provide new and updated evidence-based recommendations for the prevention of SSI and should be incorporated into comprehensive surgical quality improvement programs to improve patient safety.
We derived and tested a short form of the Center for Epidemiologic Studies Depression Scale (CES-D) for reliability and validity among a sample of well older adults in a large Health Maintenance Organization. The 10-item screening questionnaire, the CESD-10, showed good predictive accuracy when compared to the full-length 20-item version of the CES-D (kappa = .97, P < .001). Cutoff scores for depressive symptoms were > or = 16 for the full-length questionnaire and > or = 10 for the 10-item version. We discuss other potential cutoff values. The CESD-10 showed an expected positive correlation with poorer health status scores (r = .37) and a strong negative correlation with positive affect (r = -.63). Retest correlations for the CESD-10 were comparable to those in other studies (r = .71). We administered the CESD-10 again after 12 months, and scores were stable with strong correlation of r = .59.
BACKGROUND: We designed this observational cohort study to assess the association between patient-centered communication in primary care visits and subsequent health and medical care utilization. METHODS: We selected 39 family physicians at random, and 315 of their patients participated. Office visits were audiotaped and scored for patient-centered communication. In addition, patients were asked for their perceptions of the patient-centeredness of the visit. The outcomes were: (1) patients' health, assessed by a visual analogue scale on symptom discomfort and concern; (2) self-report of health, using the Medical Outcomes Study Short Form-36; and (3) medical care utilization variables of diagnostic tests, referrals, and visits to the family physician, assessed by chart review. The 2 measures of patient-centeredness were correlated with the outcomes of visits, adjusting for the clustering of patients by physician and controlling for confounding variables. RESULTS: Patient-centered communication was correlated with the patients' perceptions of finding common ground. In addition, positive perceptions (both the total score and the subscore on finding common ground) were associated with better recovery from their discomfort and concern, better emotional health 2 months later, and fewer diagnostic tests and referrals. CONCLUSIONS: Patient-centered communication influences patients' health through perceptions that their visit was patient centered, and especially through perceptions that common ground was achieved with the physician. Patient-centered practice improved health status and increased the efficiency of care by reducing diagnostic tests and referrals.
BACKGROUND: Hospitals have difficulty justifying the expense of maintaining trauma centers without strong evidence of their effectiveness. To address this gap, we examined differences in mortality between level 1 trauma centers and hospitals without a trauma center (non-trauma centers). METHODS: Mortality outcomes were compared among patients treated in 18 hospitals with a level 1 trauma center and 51 hospitals non-trauma centers located in 14 states. Patients 18 to 84 years old with a moderate-to-severe injury were eligible. Complete data were obtained for 1104 patients who died in the hospital and 4087 patients who were discharged alive. We used propensity-score weighting to adjust for observable differences between patients treated at trauma centers and those treated at non-trauma centers. RESULTS: After adjustment for differences in the case mix, the in-hospital mortality rate was significantly lower at trauma centers than at non-trauma centers (7.6 percent vs. 9.5 percent; relative risk, 0.80; 95 percent confidence interval, 0.66 to 0.98), as was the one-year mortality rate (10.4 percent vs. 13.8 percent; relative risk, 0.75; 95 percent confidence interval, 0.60 to 0.95). The effects of treatment at a trauma center varied according to the severity of injury, with evidence to suggest that differences in mortality rates were primarily confined to patients with more severe injuries. CONCLUSIONS: Our findings show that the risk of death is significantly lower when care is provided in a trauma center than in a non-trauma center and argue for continued efforts at regionalization.
Today's data centers may contain tens of thousands of computers with significant aggregate bandwidth requirements. The network architecture typically consists of a tree of routing and switching elements with progressively more specialized and expensive equipment moving up the network hierarchy. Unfortunately, even when deploying the highest-end IP switches/routers, resulting topologies may only support 50% of the aggregate bandwidth available at the edge of the network, while still incurring tremendous cost. Non-uniform bandwidth among data center nodes complicates application design and limits overall system performance. In this paper, we show how to leverage largely commodity Ethernet switches to support the full aggregate bandwidth of clusters consisting of tens of thousands of elements. Similar to how clusters of commodity computers have largely replaced more specialized SMPs and MPPs, we argue that appropriately architected and interconnected commodity switches may deliver more performance at less cost than available from today's higher-end solutions. Our approach requires no modifications to the end host network interface, operating system, or applications; critically, it is fully backward compatible with Ethernet, IP, and TCP.
In addition to maintaining the GenBank(R) nucleic acid sequence database, the National Center for Biotechnology Information (NCBI) provides data analysis and retrieval resources for the data in GenBank and other biological data made available through NCBI's website. NCBI resources include Entrez, PubMed, PubMed Central, LocusLink, the NCBI Taxonomy Browser, BLAST, BLAST Link (BLink), Electronic PCR, OrfFinder, Spidey, RefSeq, UniGene, HomoloGene, ProtEST, dbMHC, dbSNP, Cancer Chromosome Aberration Project (CCAP), Entrez Genomes and related tools, the Map Viewer, Model Maker, Evidence Viewer, Clusters of Orthologous Groups (COGs) database, Retroviral Genotyping Tools, SARS Coronavirus Resource, SAGEmap, Gene Expression Omnibus (GEO), Online Mendelian Inheritance in Man (OMIM), the Molecular Modeling Database (MMDB), the Conserved Domain Database (CDD) and the Conserved Domain Architecture Retrieval Tool (CDART). Augmenting many of the web applications are custom implementations of the BLAST program optimized to search specialized data sets. All of the resources can be accessed through the NCBI home page at: http://www.ncbi.nlm.nih.gov.
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Three-dimensional objects are commonly represented as 3D boxes in a point-cloud. This representation mimics the well-studied image-based 2D bounding-box detection but comes with additional challenges. Objects in a 3D world do not follow any particular orientation, and box-based detectors have difficulties enumerating all orientations or fitting an axis-aligned bounding box to rotated objects. In this paper, we instead propose to represent, detect, and track 3D objects as points. Our framework, CenterPoint, first detects centers of objects using a keypoint detector and regresses to other attributes, including 3D size, 3D orientation, and velocity. In a second stage, it refines these estimates using additional point features on the object. In CenterPoint, 3D object tracking simplifies to greedy closest-point matching. The resulting detection and tracking algorithm is simple, efficient, and effective. CenterPoint achieved state-of-the-art performance on the nuScenes benchmark for both 3D detection and tracking, with 65.5 NDS and 63.8 AMOTA for a single model. On the Waymo Open Dataset, Center-Point outperforms all previous single model methods by a large margin and ranks first among all Lidar-only submissions. The code and pretrained models are available at https://github.com/tianweiy/CenterPoint.
Cloud data centers host diverse applications, mixing workloads that require small predictable latency with others requiring large sustained throughput. In this environment, today's state-of-the-art TCP protocol falls short. We present measurements of a 6000 server production cluster and reveal impairments that lead to high application latencies, rooted in TCP's demands on the limited buffer space available in data center switches. For example, bandwidth hungry "background" flows build up queues at the switches, and thus impact the performance of latency sensitive "foreground" traffic.