A Jackknife Estimator for Tracking Error Variance of Optimal Portfolios Constructed Using Estimated Inputs1

We develop a jackknife estimator for the conditional variance of a minimum-tracking- error-variance portfolio constructed using estimated covariances. We empirically evaluate the performance of our estimator using an optimal portfolio of 200 stocks that has the lowest tracking error with respect to the S&P500 benchmark when three years of daily return data are used for estimating covariances. We find that our jackknife estimator provides more precise estimates and suffers less from in-sample optimism when compared to conventional estimators.

Quantum Antiferromagnetism in Quasicrystals

The antiferromagnetic Heisenberg model is studied on a two-dimensional bipartite quasiperiodic lattice. The distribution of local staggered magnetic moments is determined on finite square approximants with up to 1393 sites, using the Stochastic Series Expansion Quantum Monte Carlo method. A non-trivial inhomogeneous ground state is found. For a given local coordination number, the values of the magnetic moments are spread out, reflecting the fact that no two sites in a quasicrystal are identical. A hierarchical structure in the values of the moments is observed which arises from the self-similarity of the quasiperiodic lattice. Furthermore, the computed spin structure factor shows antiferromagnetic modulations that can be measured in neutron scattering and nuclear magnetic resonance experiments. This generic model is a first step towards understanding magnetic quasicrystals such as the recently discovered Zn-Mg-Ho icosahedral structure.Comment: RevTex, 4 pages with 5 figure

Optimal Energy-Delay Routing Protocol with Trust Levels for Wireless Ad Hoc Networks

This paper presents the Trust Level Routing (TLR) pro- tocol, an extension of the optimized energy-delay rout- ing (OEDR) protocol, focusing on the integrity, reliability and survivability of the wireless network. TLR is similar to OEDR in that they both are link state routing proto- cols that run in a proactive mode and adopt the concept of multi-point relay (MPR) nodes. However, TLR aims at incorporating trust levels into routing by frequently changing the MPR nodes as well as authenticating the source node and contents of control packets. TLR calcu- lates the link costs based on a composite metric (delay incurred, energy available at the neighbor node, energy spent during transmission and the number of packets sent on each link) for the selection ofMPR nodes. We highlight the vulnerabilities in OEDR and show ways to counter the possible attacks by using authentication and traffic par- tition as a basis for mitigating the effects of malicious activity. Network simulator NS2 results show that TLR delivers the packets with a noticeable decrease in the av- erage end-to-end delay with a small increase in the power consumed due to the additional computational overhead attributed to the security extension

A Study on Cardiovascular manifestations in Lupus Patients.

INTRODUCTION : Systemic Lupus Erythematosus (SLE) is a multisystem autoimmune disease primarily occurs in young women and characterised by varied clinical and laboratory manifestations. Severity ranges from a mild disease with rash and arthritis to a devastating illness with renal failure and central nervous system involvement. Perhaps because of the prominence of cutaneous, musculoskeletal, renal and neurological manifestations cardiac involvement has not received detailed attention. The widespread use of modern echocardiography together with the longer life spans of severe SLE patients has contributed to increased recognition of cardiovascular involvement in these patients. AIMS AND OBJECTIVES : 1. To identify the various cardiac manifestations in patients with systemic lupus erythematosus. 2. To detect the risk of association of anti cardiolipin antibodies and lupus anticoagulant with cardiac involvement in lupus patients. 3. To determine the correlation between the risk factors for atherosclerosis and carotid intima medial thickness in lupus patients. MATERIALS AND METHODS : In this prospective study, 100 consecutive patients (95 females, 5 males) with systemic lupus erythematosus (who fulfilled the1997 revision of ACR 1982 classification criteria for classification of systemic lupus erythematosus) attending the rheumatology outpatient clinic or as inpatients in the rheumatology ward of Government General Hospital, Chennai constituted the study group. This study was done during March 2007- March 2009. Inclusion criteria: Patients who fulfilled the 1997 revision of ACR 1982 classification criteria for systemic lupus erythematosus were included. Exclusion criteria: Patients with overlap syndrome, Pre-existing cardiac illness due to other causes. Patients with renal failure (defined by a serum creatinine level of 3.0 mg/dl [265moles/liter] or acreatinine clearance of 30 ml/minute). Apart from age and sex, detailed history including mode of onset, duration of illness, constitutional, mucocutaneous, musculoskeletal and symptoms pertaining to the cardiovascular system i.e. chest pain, palpitation, breathlessness, leg swelling and relevant history of other organ involvement was obtained. History of recurrent abortion if relevant, venous or arterial thrombosis and dose of steroid therapy at the time of study were noted. All patients were questioned for history of rheumatic fever, infective endocarditis, hypertension, diabetes, alcohol and smoking habits. RESULTS : There were 95 females and 5 males in the study group (Fig 1). The age of the patients varied from 11 years to 45 yrs (Fig 2). The mean age of the patients was 23±6.77 years. Disease onset in the second or third decade was common (mean age 20.83± 6.29 years). Almost one quarter of patients had childhood onset of the disease (Fig 3). The mean disease duration was 2.5±2 years. CONCLUSION : 1. Pericarditis was the most common observation followed by valvular heart disease. 2. Myocarditis, conduction abnormalities, impairment of systolic and diastolic function and pulmonary hypertension occur less frequently. 3. Significantly higher number of patients had valvular heart disease in the anticardiolipin antibody positive group. 4. SLE patients with anticardiolipin antibody positivity are 4 times more likely to have valvular heart disease, compared to their counterparts. 5. The risk of valvular heart disease is 19 times higher in lupus patients who also have secondary antiphospholipid antibody syndrome with history of recurrent abortions. 6. Dyslipidemia was found in half of the patients. 7. Patients with lupus exhibited a significantly greater IMT than controls. 8. The carotid IMT was independently related to age, systolic blood pressure and LDL cholesterol. 9. There was no relation between anticardiolipin antibodies and the carotid IMT

Open Comparative study of Melagenina Plus Lotion and Melagenina Plus Lotion along with UVA to Evaluate the Rate of Repigmentation in Vitiligo Patients.

INTRODUCTION : Vitiligo is a pigmentary disorder of universal distribution and unknown etiology with various precipitating factors. Vitiligo is asymptomatic and benign in terms of human life, of uncertain prognosis and fatal from the aesthetic point of view. It modifies the conduct of the patients, and quite frequently affects the family dynamics. Throughout history this has lead to sustained research on its etiology and to the search for a medication that will effectively induce repigmentation without undesirable side effects. At present the various therapeutic options include topical and systemic photochemotherapy with psoralens, topical and systemic steroids and immunomodulators. Off late topical tacrolimus and narrow band UVB therapy is gaining importance. Apart from medical therapies various surgical and cosmetic procedures are being carried out in patients with stable vitiligo. Since far back in time, numerous drugs for topical and systemic therapy have been used for vitiligo, many only with a placebo effect, which in their times were considered a panacea for the treatment of vitiligo. Time itself has served to discard them, be it for their inefficacy or for the higher incidence of side effects. Hence there is a need to find an alternative therapy that will offer the patient an option for improvement or cure, avoiding these side effects. Melagenina is one such biological product, manufactured in Placental Histotherapy Center, Havana, Cuba since 1973. The center claims the repigmentation rate of 80-84%, 2 years after starting treatment with Melagenina, without local and systemic side effects. It was also claimed that addition of calcium chloride to Melagenina enhances its potency and it was marketed under the name Melagenina plus lotion. This product was available in India since 2003. This product was tested in various other countries with encouraging results. The aim of our study is to find the efficacy of Melagenina plus lotion in patients with localized stable vitiligo, when used alone and in combination with UVA in our Indian population. AIM OF THE STUDY : The Aim of the study is to evaluate of the rate of repigmentation in 6 months with Melagenina plus lotion and Melagenina plus lotion along with UVA in the treatment of localized stable vitiligo. CONCLUSION : 1. Melagenina plus lotion can be effectively used as topical monotherapy for treating localized stable Vitiligo. When used alone its overall efficacy is 33.74% after a period of 6 months. 2. When Ultraviolet A radiation was combined with Melagenina plus lotion (MUVA) there was significant reduction in VASI score at an earlier date, when compared to Melagenina plus lotion monotherapy. 3. The overall efficacy of MUVA is 37.01%, which was only slightly higher than Melagenina plus lotion monotherapy. 4. Localized Vitiligo in sun exposed areas like face and upper limbs showed better response to MUVA. 5. Melagenina plus lotion was most effective in focal and segmental Vitiligo than in Vitiligo vulgaris. 6. Melagenina plus lotion was safe as there were no serious systemic or cutaneous adverse effects apart from transient erythema in a few patients

Annihilation Diagrams in Two-Body Nonleptonic Decays of Charmed Mesons

In the pole-dominance model for the two-body nonleptonic decays of charmed mesons $D \rightarrow PV$ and $D \rightarrow VV$, it is shown that the contributions of the intermediate pseudoscalar and the axial-vector meson poles cancel each other in the annihilation diagrams in the chiral limit. In the same limit, the annihilation diagrams for the $D \rightarrow PP$ decays vanish independently.Comment: 9 pages (+ 3 figures available upon request), UR-1316, ER-40685-766, IC/93/21