Browsing by Subject "Compression"

Now showing 1 - 4 of 4

Open Access
Analysis of brick wall debris for reusing
(Gazi Universitesi * Muhendislik Mimarlik Fakultesi,Gazi University * Faculty of Engineering & Architecture, 2021-03-21) Üçer Erduran, Deniz; Demirel, İsmail Ozan; Elias-Ozkan, S. T.
Tuğla duvarlar sağlam ve uzun ömürlü olmalarına rağmen farklı sebeplerle yıkıma maruz kalırlar. Bu çalışma Ankara Çiğdem Mahallesinde 1990’larda inşa edilmiş tuğla duvar dolgulu betonarme bir kooperatif binasının yıkım sürecini sunmaktadır. Yıkım sonrası atık olarak sahada biriken yatay delikli tuğla duvar parçaları incelenmiş ve yeniden kullanıma uygun olabilecekleri gözlenmiştir. Tuğlalar, sıva ve harç numuneleri laboratuvarda basınç testine, duvar parçaları da başlangıç kayma dayanımı testine tabi tutulmuştur. Elde edilen mukavemet değerleri ve ölçülen diğer fiziksel özellikler ilgili standartlardaki değerlerden yüksek olduğu için kullanılmalarının uygun olduğu sonucuna varılmış ve uygun bir yeniden kullanım metodu sunulmuştur. Son olarak, bu metot temel alınarak yıkımda oluşan genel duvar atıklarının kurtarılması için nasıl düzenlemeler yapılabileceği tartışılmıştır.
Open Access
Compressed multi-framed signature files: an index structure for fast information retrieval
(ACM, 1999-02-03) Koçberber, Seyit; Can, Fazlı
A new indexing method, called Compressed Multi-Framed Signature File (C-MFSF), that uses a partial query evaluation strategy with compressed signature bit slices is presented. In C-MFSF, a signature file is divided into variable sized compressed vertical frames with different on-bit densities to optimize the response time. Experiments with a real database of 152,850 records show that a response time less than 150 milliseconds is possible. For multi-term queries C-MFSF obtains the query results with fewer disk accesses than the inverted files. The method requires no indexing vocabulary. These attributes have important implications; for example, web search engines process multi-term queries in very large databases with sizeable vocabularies.
Open Access
Partial query evaluation for vertically partitioned signature files in very large unformatted databases
(1996) Koçberber, Seyit
Signature ﬁle approach is a well-known indexing technique. The Bit Sliced Signature File (BSSF) method provides an efﬁcient retrieval environment by only accessing on-bits of query signatures. However, its response time increases for increasing number of query terms. For BSSF we deﬁne a stopping condition that tries to avoid the processing of all on-bits of query signatures through partial evaluation. The aim of the stopping condition is to reduce the expected number of false drops to the level that also provides the lowest response time within the framework of BSSF. We propose the Partially evaluated Bit-Sliced Signature File (P-BSSF) method that employs the partial evaluation strategy and minimizes the response time in a multi-term query environment by considering the submission probabilities of the queries with different number of terms. Experiments show that P-BSSF provides 85% improvement in response time over BSSF depending on space overhead and the number of query terms. To provide better optimization of the signature ﬁle parameters in multi-term query environments, we propose Multi-Fragmented Signature File (MFSF) method as an extension of P-BSSF. In MFSF, a signature ﬁle is divided into variable sized vertical fragments with different on-bit densities to optimize the response time using a similar query evaluation methodology. In query evaluation the query signature on-bits of the lower on-bit density fragments are used first. As the number of query terms increases, the number of query signature on-bits in the lower on-bit density fragments increases and the query stopping condition is reached in fewer bit slice evaluation steps. Therefore, in MFSF, the response time decreases for an increasing number of query terms. The analysis shows that, with no space overhead, MFSF outperforms the P-BSSF and generalized frame-sliced signature file organizations. Due to hashing and superimposition operations used in obtaining signatures, the signature of an irrelevant record may match the query signature, i.e., it is possible to have false drops. In signature file processing the accurate estimation of the number of false drops is essential to obtain system parameters that will yield a desirable response time. We propose a more accurate false drop estimation method for databases with varying record lengths instead of using an average number of distinct terms per record. In this method, the records of a database are conceptually partitioned according to the number of distinct terms they contain and the number of false drops of each group is estimated separately. Experiments with real data show that depending on the space overhead, the proposed method obtains up to 33%, 25%, and 20% response time improvements for the sequential, generalized frame-sliced, and MFSF methods, respectively. For very large databases even one bit slice of MFSF may occupy several disk blocks. We propose the Compressed Multi-Fragmented Signature File (C-MFSF) method that stores the bit slices of MFSF in a compact form which provides a better response time. To minimize the number of disk accesses, the signature size and the disk block size can be adjusted such that most bit slices fit into a single disk block after compression. In such environments, C-MFSF evaluates the queries with more than two terms with only one disk access per query term rather than two disk accesses of the inverted file method which are respectively for the pointer of the query term posting list and the list itself. Our projection based on real data shows that for a database of one million records C-MFSF provides a response time of 0.85 seconds.
Open Access
A privacy-preserving solution for compressed storage and selective retrieval of genomic data
(Cold Spring Harbor Laboratory Press, 2016) Huang Z.; Ayday, E.; Lin, H.; Aiyar, R. S.; Molyneaux, A.; Xu, Z.; Fellay, J.; Steinmetz, L. M.; Hubaux, Jean-Pierre
In clinical genomics, the continuous evolution of bioinformatic algorithms and sequencing platforms makes it beneficial to store patients' complete aligned genomic data in addition to variant calls relative to a reference sequence. Due to the large size of human genome sequence data files (varying from 30 GB to 200 GB depending on coverage), two major challenges facing genomics laboratories are the costs of storage and the efficiency of the initial data processing. In addition, privacy of genomic data is becoming an increasingly serious concern, yet no standard data storage solutions exist that enable compression, encryption, and selective retrieval. Here we present a privacy-preserving solution named SECRAM (Selective retrieval on Encrypted and Compressed Reference-oriented Alignment Map) for the secure storage of compressed aligned genomic data. Our solution enables selective retrieval of encrypted data and improves the efficiency of downstream analysis (e.g., variant calling). Compared withBAM, thede factostandard for storing aligned genomic data, SECRAM uses 18%less storage. Compared with CRAM, one of the most compressed nonencrypted formats (using 34% less storage than BAM), SECRAM maintains efficient compression and downstream data processing, while allowing for unprecedented levels of security in genomic data storage. Compared with previous work, the distinguishing features of SECRAM are that (1) it is position-based insteadofread-based,and(2)itallowsrandomqueryingofasubregionfromaBAM-likefileinanencryptedform.Ourmethod thus offers a space-saving, privacy-preserving, and effective solution for the storage of clinical genomic data.