A distorted physical model to study sudden dam break flows

A distorted physical model, based upon Urkmez Dam in Izmir, Turkey, was built to study sudden dam break flows. The distorted model had a horizontal scale of 1/150 and vertical scale of 1/30, containing dam reservoir, dam body and downstream area—from dam body to Urkmez urban area until the sea coast. In the model, the reservoir is approximately 12 m3, the dam body has a width of 2.9 m and a height of 1.1 m and the downstream area is nearly 200 m2. The Ürkmez dam is chosen since it has reasonable dimensions and it is located close to Ürkmez village. The features creating roughness such as buildings, roads, plant, etc are also reflected in the physical model. The dam break problem is investigated for sudden partial collapse which is simulated by a trapezoidal breach on the dam body. The water depths are measured by using e+ WATER L (level) sensors. The velocities are determined by Ultrasonic Velocity Profiler (UVP) transducers. The propagation of the flood is recorded by a HD camera. The experimental results show that Urkmez area can be flooded in a matter of minutes, at depths reaching up to 3 meters in residential areas. The flood wave can reach in the residential areas in 4 minutes. Flood wave velocities at peak discharge can exceed 55 km/h

Regulation factors of productivity, nitrogen fixation and phytoplankton species composition in the upwelling area and the Mekong estuary off southern central Vietnam, South China Sea

Im südchinesischen Meer wird durch den Südwest- (SW) Monsun zwischen Juni und September vor der südlichen vietnamesischen Küste Auftrieb verursacht. Diese Arbeit beinhaltet die Erstbeschreibung der Produktivität des Gebietes sowie eine Abschätzung der Bedeutung von Nitrat und pelagischer Distickstoff- (N2) Fixierung als neue Stickstoffquellen für die Primärproduktion. Weiterhin wird gezeigt, dass die Flussfahne des Mekongs optimale Bedingungen für das Wachstum von Diazotrophen bietet. Dieses Ergebnis unterstützt die Hypothese, dass tropische Flüsse durch ihre Einträge von Phosphat und Eisen generell die N2 Fixierung im Meer fördern.In the South China Sea (SCS), the southwest (SW) monsoon between June and September induces coastal upwelling off southern central Vietnam. This thesis includes the first ground truth evaluation of the primary productivity of this upwelling zone, as well as an assessment of the importance of nitrate and pelagic dinitrogen (N2) fixation in fueling the productivity. Further, it was shown that Mekong River discharge sets favorable nutrient conditions for diazotrophs, which supports the hypothesis that discharge by tropical rivers might generally enhance oceanic N2 fixation

Yeraltusuyu Kirlilik Taşınım Deneyi ve Boyuna Dispersivite Değerinin Belirlenmesi

Groundwater is the safest and most important source of available freshwater. However, it is threatened by pollution arising from various activities. In this study the contaminant transport in homogeneous medium is investigated by means of an experimental set-up designed for the hydrologic cycle available in Hydraulics Laboratory. The experiments are carried out in the physical aquifer chamber 2 m long, 1 m wide and 0.10 m high. The piezometer tubes and observation wells are placed at the bottom of the chamber longitudinally and transversally. NaCl solution which represents contaminant is injected from a well instantaneously, as a point source. Electrical Conductivity (EC) values of the water are measured by using probes placed in the observation wells. Measurements are taken at specific time interval. The NaCl concentrations of the samples are determined indirectly by converting these measured EC values to concentration values by means of the calibration curve generated at the beginning of the experiments. Consequently, the longitudinal dispersivity of the porous medium was determined by solving the one dimensional advective-dispersive equation.Tatlı su kaymakları arasında yeraltısuyu en güvenilir ve en önemli kaynaktır. Ancak bu kaynaklar kirlilik tehdidiyle karşı karşıyadır. Bu çalışmada, Hidrolik laboratuarında mevcut olan Hidrolojik çevrim deney düzeneği kullanılarak homojen ortamda yeraltısuyu kirlilik taşınımı deneysel olarak incelenmiştir. Akiferin boyutları 2 m uzunluğunda, 1 m genişliğinde ve 0.10 m yüksekliğindedir. Piyezometre tüpleri ve gözlem kuyuları akiferde boyuna ve enine yönde yerleştirilmiştir. NaCl solüsyonu noktasal kirlilik kaynağı olacak şekilde bir kuyudan akifere verilmiştir. Suyun elektriksel iletkenlik değerleri gözlem kuyularından elektriksel iletkenlik probları kullanılarak ölçülmüştür. Ölçümler belirli aralıklarla gerçekleştirilmiştir. Ölçülen elektriksel iletkenlik değerleri deney başında çıkarılan kalibrasyon eğrisi yardımıyla NaCl konsantrasyonlarına dönüştürülmüştür. Sonuç olarak, gözenekli ortamın boyuna dispersivite değeri bir boyutlu adveksiyon-dispersiyon denklemi çözülerek elde edilmiştir

Calculation of the time-varying mean velocity by different methods and determination of the turbulence intensities

The raw velocity data for both stream-wise and transversal directions in unsteady flows, which are formed by generating input hydrograph, are obtained by using a flow tracker. The same hydrograph is generated 15 times and the mean values are found by calculating the average of all hydrographs. The time varying mean is obtained by using FFT, moving average, wavelet and EMD methods. The best time varying mean is selected according to prescribed criteria. Then, the 15 time series are processed and the stream-wise and transversal turbulence intensities are obtained. The mean of the product of fluctuations is also determined. © 2010 Academic Journals.TÜBİTAK (project number 106M274

Correlated Pseudorandomness from the Hardness of Quasi-Abelian Decoding

Secure computation often benefits from the use of correlated randomness to achieve fast, non-cryptographic online protocols. A recent paradigm put forth by Boyle $\textit{et al.}$ (CCS 2018, Crypto 2019) showed how pseudorandom correlation generators (PCG) can be used to generate large amounts of useful forms of correlated (pseudo)randomness, using minimal interactions followed solely by local computations, yielding silent secure two-party computation protocols (protocols where the preprocessing phase requires almost no communication). An additional property called programmability allows to extend this to build N-party protocols. However, known constructions for programmable PCG's can only produce OLE's over large fields, and use rather new splittable Ring-LPN assumption. In this work, we overcome both limitations. To this end, we introduce the quasi-abelian syndrome decoding problem (QA-SD), a family of assumptions which generalises the well-established quasi-cyclic syndrome decoding assumption. Building upon QA-SD, we construct new programmable PCG's for OLE's over any field $\mathbb{F}_q$ with $q>2$. Our analysis also sheds light on the security of the ring-LPN assumption used in Boyle $\textit{et al.}$ (Crypto 2020). Using our new PCG's, we obtain the first efficient N-party silent secure computation protocols for computing general arithmetic circuit over $\mathbb{F}_q$ for any $q>2$.Comment: This is a long version of a paper accepted at CRYPTO'2

ÜÇGEN ŞEKLİNDEKİ TAŞKIN HİDROGRAFINDAN KAYNAKLANAN TABAN MALZEMESİ TAŞINMASININ DENEYSEL ARAŞTIRILMASI

In this study, experiments are carried out in the system designed and built in Hydraulics Laboratory of DEU, involving a rectangular flume of 18.6 m length in order to investigate the sediment transport in the cases of unsteady flow. The flume experiments are conducted using different triangular shaped input hydrographs without sediment feeding at upstream. The sediment median size D50 and the standard  deviation  gσ   are  4.8  mm  and  1.4  mm,  respectively.  The  sediment  is  collected  at  the downstream end of the flume and weighed. The measured bed load values are compared with those calculated from the empirical relations given in the relevant literature for steady flow cases, assuming that they are also applicable in unsteady cases. It is found that the measured bed load values are better compatible with those calculated from the expression given by Engelund and Fredsoe (1976).Bu çalışma kapsamında, DEÜ Hidrolik Laboratuvarında mevcut 18,6 m uzunluğundaki kanalda zamanla değişen akım rejiminde sürüntü maddesi hareketi incelenmiştir. Deneyler üçgen şeklindeki farklı  giriş  hidrografları  kullanılarak  ve  membadan  sürüntü  maddesi  beselemesi  olmadan gerçekleştirilmiştir. Kanal tabanına D50= 4,8 mm, standart sapması  gσ =1,4 mm olan üniform malzeme serilmiştir. Kanal mansabında bulunan sepetlerde toplanan malzeme tartılarak sürüntü maddesi yükü belirlenmiş ve bu değerler ‐literatürde verilen ampirik denklemlerin zamanla değişen akımlar için de uygulanabilir olduğu kabulüyle ‐ hesaplananlar ile karşılaştırılmıştır. Deneysel bulguların, konuyla ilgili literatürde yer alan denklemlerden Engelund ve Fredsoe (1976) tarafından verilen ampirik bağıntı ile daha çok uyumlu olduğu görülmüştür.

On the Independence Assumption in Quasi-Cyclic Code-Based Cryptography

Cryptography based on the presumed hardness of decoding codes -- i.e., code-based cryptography -- has recently seen increased interest due to its plausible security against quantum attackers. Notably, of the four proposals for the NIST post-quantum standardization process that were advanced to their fourth round for further review, two were code-based. The most efficient proposals -- including HQC and BIKE, the NIST submissions alluded to above -- in fact rely on the presumed hardness of decoding structured codes. Of particular relevance to our work, HQC is based on quasi-cyclic codes, which are codes generated by matrices consisting of two cyclic blocks. In particular, the security analysis of HQC requires a precise understanding of the Decryption Failure Rate (DFR), whose analysis relies on the following heuristic: given random sparse vectors $e_1,e_2$ (say, each coordinate is i.i.d. Bernoulli) multiplied by fixed sparse quasi-cyclic matrices $A_1,A_2$, the weight of resulting vector $e_1A_1+e_2A_2$ is very concentrated around its expectation. In the documentation, the authors model the distribution of $e_1A_1+e_2A_2$ as a vector with independent coordinates (and correct marginal distribution). However, we uncover cases where this modeling fails. While this does not invalidate the (empirically verified) heuristic that the weight of $e_1A_1+e_2A_2$ is concentrated, it does suggest that the behavior of the noise is a bit more subtle than previously predicted. Lastly, we also discuss implications of our result for potential worst-case to average-case reductions for quasi-cyclic codes

Comparative genomics reveals surprising divergence of two closely related strains of uncultivated UCYN-A cyanobacteria

Marine planktonic cyanobacteria capable of fixing molecular nitrogen (termed 'diazotrophs') are key in biogeochemical cycling, and the nitrogen fixed is one of the major external sources of nitrogen to the open ocean. Candidatus Atelocyanobacterium thalassa (UCYN-A) is a diazotrophic cyanobacterium known for its widespread geographic distribution in tropical and subtropical oligotrophic oceans, unusually reduced genome and symbiosis with a single-celled prymnesiophyte alga. Recently a novel strain of this organism was also detected in coastal waters sampled from the Scripps Institute of Oceanography pier. We analyzed the metagenome of this UCYN-A2 population by concentrating cells by flow cytometry. Phylogenomic analysis provided strong bootstrap support for the monophyly of UCYN-A (here called UCYN-A1) and UCYN-A2 within the marine Crocosphaera sp. and Cyanothece sp. clade. UCYN-A2 shares 1159 of the 1200 UCYN-A1 protein-coding genes (96.6%) with high synteny, yet the average amino-acid sequence identity between these orthologs is only 86%. UCYN-A2 lacks the same major pathways and proteins that are absent in UCYN-A1, suggesting that both strains can be grouped at the same functional and ecological level. Our results suggest that UCYN-A1 and UCYN-A2 had a common ancestor and diverged after genome reduction. These two variants may reflect adaptation of the host to different niches, which could be coastal and open ocean habitats

On the independence assumption in quasi-cyclic code-based cryptography

Cryptography based on the presumed hardness of decoding codes – i.e., code-based cryptography – has recently seen increased interest due to its plausible security against quantum attackers. Notably, of the four proposals for the NIST post-quantum standardization process that were advanced to their fourth round for further review, two were code-based. The most efficient proposals – including HQC and BIKE, the NIST submissions alluded to above – in fact rely on the presumed hardness of decoding structured codes. Of particular relevance to our work, HQC is based on quasi-cyclic codes, which are codes generated by matrices consisting of two cyclic blocks. In particular, the security analysis of HQC requires a precise un- derstanding of the Decryption Failure Rate (DFR), whose analysis relies on the following heuristic: given random “sparse” vectors e1, e2 (say, each coordinate is i.i.d. Bernoulli) multiplied by fixed “sparse” quasi-cyclic matrices A1, A2, the weight of resulting vector e1A1 + e2A2 is very concentrated around its expectation. In the documentation, the authors model the distribution of e1A1 + e2A2 as a vector with inde- pendent coordinates (and correct marginal distribution). However, we uncover cases where this modeling fails. While this does not invalidate the (empirically verified) heuristic that the weight of e1A1 + e2A2 is concentrated, it does suggest that the behavior of the noise is a bit more subtle than previously predicted. Lastly, we also discuss implications of our result for potential worst-case to average-case reductions for quasi-cyclic codes