The Casimir Effect in Spheroidal Geometries

We study the zero point energy of massless scalar and vector fields subject to spheroidal boundary conditions. For massless scalar fields and small ellipticity the zero-point energy can be found using both zeta function and Green's function methods. The result agrees with the conjecture that the zero point energy for a boundary remains constant under small deformations of the boundary that preserve volume (the boundary deformation conjecture), formulated in the case of an elliptic-cylindrical boundary. In the case of massless vector fields, an exact solution is not possible. We show that a zonal approximation disagrees with the result of the boundary deformation conjecture. Applying our results to the MIT bag model, we find that the zero point energy of the bag should stabilize the bag against deformations from a spherical shape.Comment: 24 pages, 3 figures. To appear in Phys. Rev.

A combined NMR and DFT study of Narrow Gap Semiconductors: The case of PbTe

In this study we present an alternative approach to separating contributions to the NMR shift originating from the Knight shift and chemical shielding by a combination of experimental solid-state NMR results and ab initio calculations. The chemical and Knight shifts are normally distinguished through detailed studies of the resonance frequency as function of temperature and carrier concentration, followed by extrapolation of the shift to zero carrier concentration. This approach is time-consuming and requires studies of multiple samples. Here, we analyzed $^{207}$Pb and $^{125}$Te NMR spin-lattice relaxation rates and NMR shifts for bulk and nanoscale PbTe. The shifts are compared with calculations of the $^{207}$Pb and $^{125}$Te chemical shift resonances to determine the chemical shift at zero charge carrier concentration. The results are in good agreement with literature values from carrier concentration-dependent studies. The measurements are also compared to literature reports of the $^{207}$Pb and $^{125}$Te Knight shifts of $n$- and $p$-type PbTe semiconductors. The literature data have been converted to the currently accepted shift scale. We also provide possible evidence for the "self-cleaning effect" property of PbTe nanocrystals whereby defects are removed from the core of the particles, while preserving the crystal structure.Comment: 34 pages, 9 figure

Tinjauan Momen Lentur Pelat Dua Arah Dengan Metode Perencanaan Langsung Dan Metode Elemen Hingga

This research conducted to study and determine the bending moment plate by using the DirectDesign Method and Finite Element Method. In the procedure of calculation of concrete structuresfor buildings, namely SNI 2847 2013 has been set up several plates planning methods one ofwhich is a method of using the Direct Design Method analysis. Finite element method (FEM) isdividing a complex problem into small elements where a simpler solution can be easily obtained.The theory used in plate analysis with the FEM is Kirchhoff-Love theory in which the limits areused specifically for the analysis of thin plates with small deflections by ignoring the transverseshear forces. The program is used by applying the Finite Element Method in this study is aMicrosoft Excel as a tool for calculations and modeling program SAP 2000 as a plate structure.From the calculations that the value of deflection and the bending moment on the plate twodirections with varying results.From the results obtained show that the static moments of totalfactored Direct Planning Method and the Finite Element Method showed results equal to eachother . Distribution moments on the foundation and interior plate field differently due to directPlanning Method using a great moment coefficients in pedestal while the Finite Element Methodusing transition stiffness matri

PENGARUH BIOURINE SAPI TERHADAP PERTUMBUHAN BIBIT KARET (Hevea brasiliensis Mull. Arg) ASAL STUM MATA TIDUR (The Effect of Cattle Biourine to The Growth of Rubber Seedling from Stum Rubber)

The objective of this research was to determine the best biourine concentration on the rubber seedling. This research was conducted at Teaching and Research Farm, Agriculture Faculty, Mendalo Darat, Jambi. This experiment was designed using completely Randomized Design with five treatment, and three replications. The treatments were  the level of biourine concentration : uo= 0% bio-urine, u1= 2,5%, u2= 5,0%, u3= 7,5% dan u4= 10,0%. Three were 15 units of treatments. Statical analysis showed that cattle biourine  at  7, 5 % gave the best growth of rubber seedling, shoot height and root dry weight. Key word: Urine , rubber, shoo

EFFECT OF GEOMETRIC CONFIGURATIONS ON HYDRODYNAMIC PERFORMANCE ASSESSMENT OF A MARINE PROPELLER

The present paper deals with the effect of the geometric characteristics on the propeller hydrodynamic performances. Several propeller configurations are created by changing number of blades, expanded area and pitch ratios. The Reynolds-Averaged Navier-Stokes (RANS) equations are solved using the commercial code FLUENT 6.3.26. The standar

Analisis Hubungan Pendapatan Asli Daerah, Dana Alokasi Umum, dan Dana Alokasi Khusus Atas Belanja Modal pada Pemerintah Daerah Kabupaten Tolitoli Provinsi Sulawesi Tengah

Local governments need to increase capital investment in fixed assets, such as: equipments, buildings, infrastructures, and other fixed assets. Capital expenditure allocation was based on the local needs for facilities and infrastructure. The higher level of capital investment expected to improve the quality of public services, because the fixed assets due to capital expenditure is a key for the implementation of governmental duties and provides services to the public.This study was aimed at analyzing the corelations of local own revenues, general allocation funds, and specific allocation funds with capital expenditures at Tolitoli Regency in Central Sulawesi Province. Research design methods is the field research by correlation analysis.Test results showed a lack relationship between local own revenues with capital expenditures by R value was 0,155. Meanwhile the relationship between general allocation funds with capital expenditures was 0,981 and special allocation funds with capital expenditures was 0,427. It shows the close relationship between the two variables with capital expenditures

Minimal Absorption Measurements

We show that it is not possible to discriminate two close transparencies without a certain number of photons being absorbed. We extend this to the discrimination of patterns of transparency (images).Comment: 11 pages (latex

Kemampuan Fitoremediasi Salvinia Molesta D. S. Mitchell pada Beberapa Konsentrasi Limbah Cair Minyak Bumi

Penelitian tentang Kemampuan Fitoremediasi Salvinia molesta D.S. Mitchell pada Bebera-pa Konsentrasi Limbah Cair Minyak Bumi telah dilaksanakan pada Mei sampai Juni 2011. Tujuan penelitian ini untuk mengetahui kemampuan fitoremediasi S. molesta pada beberapa konsentrasi limbah cair minyak bumi dengan mengukur TPH (Total Petroleum Hidrokarbon), pH dan berat basah. Penelitian ini dilakukan dengan menggunakan Rancangan Acak Lengkap (RAL) dengan perlakuan konsentrasi limbah 0%, 15%, 30%, 45%, 60% dan 75%, dan masing-masing perlakuan diulang 4 kali. Hasil penelitian menunjukkan bahwa S. molesta mampu menurunkan TPH pada tiap perlakuan konsentrasi limbah cair minyak bumi, dengan penurunan TPH tertinggi diperoleh pada konsentrasi limbah 75%, yaitu sebesar 1317 ppm. Pada fitoremediasi limbah cair minyak bumi menggunakan S. molesta terjadi penurunan pH yang stabil. Pertumbuhan S. molesta yang tepat pada fitoremediasi limbah cair minyak bumi diperoleh pada konsentrasi limbah 60%, dengan per-tambahan berat basah selama 30 hari sebesar 68,85 g. Dari hasil yang diperoleh, dapat disimpul-kan bahwa konsentrasi limbah cair minyak bumi yang tepat untuk proses fitoremediasi dan per-tumbuhan S. molesta diperoleh pada konsentrasi limbah 60%, dengan penurunan TPH 1157 ppm

Characterization of ultrafine grained AA 6082 Aluminum alloys modified with Zr-Sc and processed by Equal Channel Angular Pressing

Günümüz dünyasındaki global yarış, malzeme mühendisliği alanında da yeni teknolojileri ve üretim yöntemlerini beraberinde getirmektedir. Bu kapsamda geliştirilen yöntemlerden bir tanesi Aşırı Plastik Deformasyon(APD) tekniğidir. APD tekniklerinden en popüler olanı Eş Kanallı Açısal Ekstrüzyon/Pres-EKAE/P (Equal Channel Angular Extrusion/Pres) yöntemidir. Alüminyum alaşımları ise APD uygulamalarında en çok kullanılan alaşımdır. Alüminyum alaşımlarının üzerinde yoğunlaşmanın en önemli nedenlerinden biri, EKAP sonrası yapılacak yaşlandırma ısıl işlemleri ile mekanik özelliklerinin en üst seviyelere taşınabilmesidir. Ancak yüksek deformasyon sonrasında yapı, deformasyon enerjisinden dolayı kararsız hale geçmektedir ve özellikle aşırı plastik deformasyonlardan sonra yapılacak yaşlandırma ya da yüksek sıcaklıkta şekillendirme (süperplastisite) işlemlerinde hızlı bir şekilde yeniden kristalleşmeye uğramaktadır. Bundan dolayı alüminyum alaşımlarında yeniden kristalleşmeyi önlemek ve yüksek sıcaklık proses şartlarından etkilenmemesini sağlamak amacıyla Zr ve Sc gibi yeniden kristalleşmeyi geciktiren alaşım elementleri ilavesi yapılması gerekmektedir. Bu çalışmada EKAP tekniği kullanılarak AA 6082 ve AA 6082-Zr-Sc alaşımları aşırı plastik deformasyona tabi tutulmuş ve daha sonra EKAP işlemi görmüş alaşımlara farklı sıcaklıklarda yaşlandırma ısıl işlemleri yapılmıştır. Sonuç malzemelere mikroyapı karakterizasyonu yapılarak EKAP ve yaşlandırma ısıl işleminin etkileri incelenmiştir. EKAP sonunda her iki malzemenin ulaştığı sertlik değerleri aynı olmuştur. Zr ve Sc içeren alaşımın yüksek sıcaklıklarda dahi EKAP sonrası ulaştığı yapıyı ve sertlik değerlerini koruduğu, Zr ve Sc içermeyen AA 6082 alaşımının ise düşük sıcaklıklarda yeniden kristalleşmeye uğradığı tespit edilmiştir. Zr ve Sc ilavesinin EKAP öncesi ve sonrasında mikroyapının gelişiminde pozitif yönde etkili olduğu belirlenmiştir. Anahtar Kelimeler: Aşırı plastik deformasyon, eş kanallı açısal pres, alüminyum alaşımları, AA 6082 alüminyum alaşımı, Zr ve Sc ilavesi.Today’s global competitions bring together new technologies and production methods in materials engineering. In the recent years, in parallel to development of nano technologies, intensive studies are made on nano structured materials and their production methods. In these studies, new production methods are developed for producing nanomaterials, which exhibits numerous superior properties. One of these new production methods is severe plastic deformation. Severe plastic deformation (SPD) has emerged as a promising method to produce ultrafine-grained materials with attractive properties and today the SPD techniques are rapidly developing and are moving from lab-scale research into commercial production. Equal Channel Angular Pres (ECAP) is an effective method of enhancing the strength of metallic alloys through (sub) grain refinement to the submicrometer level by introducing intensive plastic deformation into materials through repetitive pressing. In the past several decades, the aluminum alloys of 6xxx group have been studied extensively because of their technological importance and their exceptional increase in strength obtained by precipitation hardening. AA 6082 alloy is one of the most popular alloys that are widely used for medium strength structural and automotive industry applications. In this study, due to its wide range of application, AA 6082 was used and ECAP was chosen as a severe plastic deformation technique. The measured mechanical properties were compared with the commercially produced AA 6082 alloy. Furthermore, the effect of Zr and Sc additions to the AA 6082 alloy were investigated. The aim of this study is to produce ultrafine-grained AA 6082 aluminum alloys that will be an alternative to commercially produced 6XXX alloys. The aluminum samples were subjected to ECAP process at room temperatures using the Bc route, which means rotation of the samples, is 90o after each pass for a maximum 4 passes. MoS2 was used as lubricant to reduce friction between the samples and die. The two intersecting channels of the ECAP die had an angle of Φ: 90o and the outer arc of curvature of ψ:20o. This configuration induces an equivalent strain of approximately 1 after each pass. ECAP processed and post-ECAP aged samples was examined by transmission electron microscope (TEM). Samples were prepared by longitudinally cutting 1 mm thick disks from the billets, manually grinding and polishing. Twin jet electrolytic thinning was then carried out at –35°C with a 30% HNO3 solution in methanol at 18 V. Differential scanning calorimetry (DSC) was employed to identify the precipitation reactions. The cell was equilibrated at 25ºC and then heated to 600ºC at 10?C/min in a dynamic argon atmosphere (1 l/h). Pre-ECAP solid-solution treatment combined with post-ECAP aging treatment has been found to be effective in enhancing the strength of AA 6082 aluminum alloys. An increase of 33% in Vickers hardness was obtained in the post-ECAP aged material in 100oC-8h (140 HV) compared to the T6 treated commercial AA 6082 Aluminum alloy (105 HV). At higher aging temperature (more than 100oC for AA 6082 and more than 180oC for AA 6082-Zr-Sc after 1st pass), the both alloys showed an increasing softening with time due to recovery or/and grain coarsening. Deformation introduced during ECAP process was shown to have a big impact on the DSC analysis of both alloys. Deformation accelerated the precipitation of Mg2Si particles. The precipitation of the β” and β’ phases occurred at significantly lower temperatures with increasing ECAP strain. The presence of Sc did not affect significantly the precipitation cycle occurred in the AlMgSi alloys. While AA 6082 alloys showed the recyrstallization (RX) peak in DSC runs, the RX peak did not occurred in the AA 6082-Zr-Sc alloys due to the effect of the recrystallization retarding elements. Zr and Sc containing AA 6082 alloy showed a greater structure stability compared to commercial AA 6082 alloys.  Keywords: Severe plastic deformation, ECAP, aluminum alloys, AA 6082, Zr and Sc additions