Sharif Digital Repository

We study a speci?c class of black holes which are called extremal. By de?ning extremality asdouble-horizon condition and imposing ?niteness assumption, we show that the dynamics of ?eldsat the horizon decouples from the rest of space. This decoupling occurs by vanishing all radialderivatives. We show this decoupling for the extremal black holes in the theories of gravity correctedby f(R)terms.We also show that these two above conditions leads to AdS × S1 near horizon geometry2of rotating black holes. This geometry which preserve SO(2, 1) × U(1) isometry group, is recentlyused in improving the entropy function method. Finally we show that decoupled equations of horizon can be derived from a... 

Dynamic searchable encryption schemes enable keyword search query and update operations on encrypted data. One of their applications is to use them in cloud storage services that allow the client to store, search and update data on an external server. Due to the importance of efficiency in real-world applications, retrieving information in searchable schemes involves leakage of some information such as search and access patterns. However, with the addition of update operations (insertion and deletion), more leakages are considered for these schemes. In this regard, reducing the amount of information disclosed to the server is necessary. For this purpose, forward and backward security... 

Weexaminetherelationshipbetweenfamilysizeandchildreneducationaloutcomes. Using a 2 percent sample of Iran Populaion Census 2011, we construct a sample of school age children. Estimation using unrestricted OLS with controls shows an inverse-U relationship between family size and educational outcomes; children educational performance improves significantly as their number increases form 1 to 2, but for families with 3 or more children, increasing the number of childern deteriorates educational outcomes  

According to the AdS/CFT correspondance,Gravity in an asymptotically AdS spacetimes has a conformal field theory dual. One of the perplexing concepts in theoretical physics is obtaining a comprehensive understanding of holography. To this end, it is of interest to explore whether holography exists beyond the known example of the AdS/CFT correspondence and for spacetimes other than the AdS. asymptotically flat spacetimes are of great theoretical importance.A correspondence has recentlay been proposed,which is between asymptotically flat spacetimes and a field theory with Galilean conformal symmerty and it is known as BMS/GCA correspondance.In this thsis,we have reviewed this correspondence... 

Imaging using ultrasonic waves is one of the common non-invasive diagnostic methods which have gained a lot of attention in recent years. The imaging resolution depends mainly on the center frequency of the ultrasonic transducer. High frequency ultrasonic imaging is mainly used in intravascular, skin and eye diseases and also in small animal studies. The main Goal of this thesis is to design two high frequency ultrasound imaging probes (between 10 to 50 MHz) which millimetric dimensions which can be used to image skin, eye or intravascular systems. In this thesis after discussing the science of high frequency ultrasound and reviewing the importance papers and books on the subject, two... 

Selection of development methodologies according to the specifications of software development projects continues to be an important challenge for the software industry. Despite the growth of software methodologies, this problem has not been fully resolved yet. Software engineers have realized, however, that there is no general-purpose methodology which is suitable for all situations. Therefore, the necessity of Situational Method Engineering (SME) has become apparent, and engineers have started to use different methods for engineering software processes to fit the project situation at hand. Assembly-based, Extension-based and Paradigm-based approaches are the SME methods prevalently used... 

Event-based embedded systems are usually energy-constrained and also have to be highly reliable. This thesis presents a novel energy-efficient standby-sparing technique for eventbased embedded systems. It speculatively pre-executes reaction tasks prior to events, resulting in a high available slack time for energy management. Although the prediction might be wrong, we will show that in average the proposed speculative standby-sparing technique (SSS) consumes less energy compared to non-speculative techniques. We present some real-life examples of event-based embedded systems to justify practical use for the proposed technique. To evaluate SSS extensive experiments were conducted on a variety... 

In recent years, high interest in using virtualization platforms and Virtual Machines (VMs) in enterprise data centers and Clouds has significantly increased the demand for high performance data storage systems. Recent studies in virtualized platforms have suggested using high-performance storage elements such as Solid-State Drives (SSDs) as a caching layer for storage subsystems mainly built upon Hard Disk Drives (HDDs). Such studies implicitly focus on sharing and partitioning the I/O cache space between VMs, while they neglect to address other important parameters such as SSD lifetime, reliability, and cache policies, which can significantly affect the efficiency of I/O caching in terms... 

nowadays Acoustic play an important role in the treatment of various diseases, especially cancer. in 2020 cancer has been the cause of death for more than 10 million patients. High intensity focused ultrasound is a non-invasive technique that used successfully to treat Malignant cancers like liver, pancreas and prostate. One of the major problems of using acoustic waves is the absorption of high frequency waves by the tissue before reaching the target area. in this study, a finite element model used to find the relation between frequency and acoustic pressure of transducer and focal region intensity. the results show, the maximum intensity in focal region linearly proportional to frequency...