A Constant Factor Approximation for Capacitated Min-Max Tree Cover

Given a graph G = (V,E) with non-negative real edge lengths and an integer parameter k, the (uncapacitated) Min-Max Tree Cover problem seeks to find a set of at most k trees which together span V and each tree is a subgraph of G. The objective is to minimize the maximum length among all the trees. In this paper, we consider a capacitated generalization of the above and give the first constant factor approximation algorithm. In the capacitated version, there is a hard uniform capacity (?) on the number of vertices a tree can cover. Our result extends to the rooted version of the problem, where we are given a set of k root vertices, R and each of the covering trees is required to include a distinct vertex in R as the root. Prior to our work, the only result known was a (2k-1)-approximation algorithm for the special case when the total number of vertices in the graph is k? [Guttmann-Beck and Hassin, J. of Algorithms, 1997]. Our technique circumvents the difficulty of using the minimum spanning tree of the graph as a lower bound, which is standard for the uncapacitated version of the problem [Even et al.,OR Letters 2004] [Khani et al.,Algorithmica 2010]. Instead, we use Steiner trees that cover ? vertices along with an iterative refinement procedure that ensures that the output trees have low cost and the vertices are well distributed among the trees

Study of Bitcoin Address Graph: Linking Addresses and Estimating Overall Balance of a User

Bitcoin has become a popular electronic currency in recent years. It is a virtual currency with no central authority and relies on a peer to peer network. The bitcoin transactions that are carried out over the network are recorded and stored in a public ledger which is accessible to every peer in the network. The sender and receiver for each transaction are identified only by cryptographic public Bitcoin ID or addresses that are generated through bitcoin wallets. While Bitcoin’s presumed anonymity offers new avenues for commerce, several recent studies have suggested otherwise. In this paper we explore the anonymity of Bitcoin system. We start by collecting user data from a popular bitcoin forum, where we scrape the address along with the username from the posts made by 1,460 users. Next we extract the transaction details from the blockchain, and construct an address graph that shows the flow of bitcoins in the network. We annotate the graph by linking all public Bitcoin ID to a user. Linking addresses gives an estimate of the overall bitcoin balance of a user. We also look up the transaction details of each user, in order to find a link between them and some well-known addresses. We were able to find few users from our study who made donations to WikiLeaks and who were frequent visitors to gambling sites. We also found a user who performed a transaction with Silkroad owner Dread Robert Pirates, which suggests that the user might have purchased some illicit item from the website.Computer Scienc

Optimization of communication intensive applications on HPC networks

Communication is a necessary but overhead inducing component of parallel programming. Its impact on application design and performance is due to several related aspects of a parallel job execution: network topology, routing protocol, suitability of algorithm being used to the network, job placement, etc. This thesis is aimed at developing an understanding of how communication plays out on networks of high performance computing systems and exploring methods that can be used to improve communication performance of large scale applications. Broadly speaking, three topics have been studied in detail in this thesis. The first of these topics is task mapping and job placement on practical installations of torus and dragonfly networks. Next, use of supervised learning algorithms for conducting diagnostic studies of how communication evolves on networks is explored. Finally, efficacy of packet-level simulations for prediction-based studies of communication performance on different networks using different network parameters is analyzed. The primary contribution of this thesis is development of scalable diagnostic and prediction methods that can assist in the process of network designing, adapting applications to future systems, and optimizing execution of applications on existing systems. These meth- ods include a supervised learning approach, a functional modeling tool (called Damselfly), and a PDES-based packet level simulator (called TraceR), all of which are described in this thesis

A zero voltage switching boost converter using a soft switching auxiliary circuit with reduced conduction losses

Modern AC-DC power supplies utilize power factor correction in order to minimize the harmonics in the input current drawn from the utility. The Boost topology is the most popular topology for power factor correction today but it has some disadvantages like very high EMI due to reverse recovery of the boost diode and high switching losses caused by hard switching of the boost switch. Many variations of the original boost topology have been suggested to overcome these problems. The Zero Voltage Transition Boost converter is one such solution. In such a converter an auxiliary resonant circuit is employed which is activated only when the boost switch is turning on or off. This auxiliary circuit allows the boost switch to turn on and off under zero voltage conditions thus reducing the switching losses. However the auxiliary circuit might be very complex and conduction losses in it might offset the expected rise in efficiency. In this thesis a soft-switching boost power converter is proposed and analyzed. This converter reduces the EMI and increases the efficiency because the auxiliary circuit is itself soft-switching and has low conduction losses due to creative placement of the resonant capacitors. Characteristic curves are generated for the proposed converter which not only give valuable insight on the behavior of the converter but also aid in designing the converter. The feasibility of the proposed converter is examined by means of results obtained from an experimental prototype

Clinical and hematological profile of pancytopenia in a tertiary care hospital of Southern Odisha, India

Background: Pancytopenia (anemia, thrombocytopenia and leukopenia) is a common haematological condition with various etiologies like ineffective haematopoiesis, bone marrow suppression, bone marrow infiltration and peripheral destruction of blood cells. The present study was done to see the clinical features and etiologies of pancytopenia in this geographical region.Methods: About 150 patients above 15 years of age after fulfilling the inclusion criteria were included in the study. They were evaluated with appropriate laboratory tests including bone marrow study, if indicated to find out the underlying etiology.Results: Common symptoms were generalized weakness (93.3%), fever (75.3%) and dyspnoea (54%). Common physical findings were pallor (100%), lymphadenopathy (43.6%) and hepatosplenomegaly (32%). Most common causes were aplastic anemia (28%), megaloblastic anemia (20%) followed by infections like malaria (13.3%), dengue (5.3%) and sepsis (1.3%). Bone marrow was hypocellular in 50 patients (41.7%), hypercellular in 45 patients (37.5%) and normocellular in 25 patients (20.8%).Conclusions: There are some reversible causes of pancytopenia like megaloblastic anemia, malaria, dengue and sepsis. Conditions like disseminated TB, collagen vascular diseases also can be treated with specific treatment if diagnosed early to avoid further complications

Understanding sports hernia (athletic pubalgia) - The anatomic and pathophysiologic basis for abdominal and groin pain in athletes

Recent publicity and some scientific reports suggest increasing success in treating an entity called “sports hernia” - more accurately named athletic pubalgia. The primary purpose of this article is to portray what we believe to be the key concept for understanding this wide variety of abdominal and groin injuries that afflict high performance athletes. These injuries have been plaguing athletes for a long time, and past treatments, based on concepts of occult hernia or simple strains, have generally failed. The former concepts do not take into account the likely mechanisms of injury or various patterns of pain that these athletes exhibit. The authors believe that the concept of a pubic joint or pubic dynamic complex is fundamental to understanding the anatomy and pertinent pathophysiology in these patients. Many injuries can now be treated successfully. Some of the injuries require surgery and others do not. In most cases, decisions regarding treatment and timing for return to full play require proper identification of the problems and consideration of a wide variety of medical, social, and business factors

Reduced erbium-doped ceria nanoparticles: one nano-host applicable for simultaneous optical down- and up-conversions

This paper introduces a new synthesis procedure to form erbium-doped ceria nanoparticles (EDC NPs) that can act as an optical medium for both up-conversion and down-conversion in the same time. This synthesis process results qualitatively in a high concentration of Ce(3+) ions required to obtain high fluorescence efficiency in the down-conversion process. Simultaneously, the synthesized nanoparticles contain the molecular energy levels of erbium that are required for up-conversion. Therefore, the synthesized EDC NPs can emit visible light when excited with either UV or IR photons. This opens new opportunities for applications where emission of light via both up- and down-conversions from a single nanomaterial is desired such as solar cells and bio-imaging

Opioids Delay Healing of Spinal Fusion: A Rabbit Posterolateral Lumbar Fusion Model

Background Context Opioid use is prevalent in the management of pre- and postoperative pain in patients undergoing spinal fusion. There is evidence that opioids downregulate osteoblasts in vitro, and a previous study found that morphine delays the maturation and remodeling of callus in a rat femur fracture model. However, the effect of opioids on healing of spinal fusion has not been investigated before. Isolating the effect of opioid exposure in humans would be limited by the numerous confounding factors that affect fusion healing. Therefore, we have used a well-established rabbit model to study the process of spinal fusion healing that closely mimics humans. Purpose The objective of this work was to study the effect of systemic opioids on the process of healing of spinal fusion in a rabbit posterolateral spinal fusion model. Study Design/Setting This is a preclinical animal study. Materials and Methods Twenty-four adult New Zealand white rabbits were studied in two groups after approval from the Institutional Animal Care and Use Committee (IACUC). The opioid group (n=12) received 4 weeks\u27 preoperative and 6 weeks\u27 postoperative transdermal fentanyl. Serum fentanyl levels were measured just before surgery and 4 weeks postoperatively to ensure adequate levels. The control group (n=12) received only perioperative pain control as necessary. All animals underwent a bilateral L5–L6 posterolateral spinal fusion using iliac crest autograft. Animals were euthanized at the 6-week postoperative time point, and assessment of fusion was done by manual palpation, plain radiographs, microcomputed tomography (microCT), and histology. Results Twelve animals in the control group and 11 animals in the opioid group were available for analysis at the end of 6 weeks. The fusion scores on manual palpation, radiographs, and microCT were not statistically different. Three-dimensional microCT morphometry found that the fusion mass in the opioid group had a lower bone volume (p=.09), a lower trabecular number (p=.02), and a higher trabecular separation (p=.02) compared with the control group. Histologic analysis found areas of incorporation of autograft and unincorporated graft fragments in both groups. In the control group, there was remodeling of de novo woven bone to lamellar organization with incorporation of osteocytes, formation of mature marrow, and relative paucity of hypertrophied osteoblasts lining new bone. Sections from the opioid group showed formation of de novo woven bone, and hypertrophied osteoblasts were seen lining the new bone. There were no sections showing lamellar organization and development of mature marrow elements in the opioid group. Less dense trabeculae on microCT correlated with histologic findings of relatively immature fusion mass in the opioid group. Conclusions Systemic opioids led to an inferior quality fusion mass with delay in maturation and remodeling at 6 weeks in this rabbit spinal fusion model. These preliminary results lay the foundation for further research to investigate underlying cellular mechanisms, the temporal fusion process, and the dose-duration relationship of opioids responsible for our findings