Sharif Digital Repository

We propose a cosmological model, üΛCDM, based on "über gravity," which is a canonical ensemble average of many theories of gravity. In this model, we have a sharp transition from (a purely) ΛCDM era to a phase in which the Ricci scalar is a constant. This transition occurs when the Ricci scalar reaches a critical scale or alternatively a transition redshift, z. We use the observations of baryonic acoustic oscillations and supernovae Ia, as well as the cosmic microwave background data to constrain üΛCDM. This yields H0=70.6-1.3+1.1 km/s/Mpc, ωm=0.2861±0.0092, and z=0.537-0.375+0.277, providing a marginally better fit with a Akaike information criterion of 0.8. Therefore, üΛCDM can ease the H0... 

The observed discrepancy of the Hubble parameter measurements in the local universe with the cosmic microwave background (CMB) data may indicate a new physics. It is vital to test the alternative models that reconcile the Hubble tension with other cosmological observations in this direction. The CMB lensing is a crucial observation that relates the early universe perturbations to the matter's late-time distribution. In this work, we study the prediction of the üΛCDM as a solution for H0 tension for CMB lensing and the low- and high-ℓ's temperature (TT) power spectrum internal inconsistency. We show that this model relaxes the low- and high-ℓ's TT mild inconsistency and the CMB lensing... 

We have studied the cosmic microwave background (CMB) map looking for features beyond cosmological isotropy. We began by tiling the CMB variance maps (which are produced by different smoothing scales) with stripes of different sizes along the most prominent dipole direction. We were able to confirm previous findings regarding the significance of the dipole. Furthermore, we discovered that some of the higher multipoles exhibit significance comparable to the dipole that naturally depends on the smoothing scales. In the end, we discussed this result having an eye on the look-elsewhere-effect. We believe our results may indicate an anomalous patch in the CMB sky that warrants further... 

The authors carried out the study to prepare chitosan N-isopropylacrylamide hydrogel via heating and radiation processes. Properties investigation of prepared samples revealed that radiation prepared samples show higher yield and swelling ratios in comparison with the heating prepared ones. Effects of hydrogel addition to drilling mud on its important rheological properties such as apparent viscosity, plastic viscosity, and stress-strain behavior are measured. The rheological properties of hydrogel were compared with cellulosemethylcarboxyl and resins that are widely used in drilling fluid. The results demonstrate that whereas linear polymer effects on mud properties are more significant in... 

The nanofibers prepared by electrospinning process have high potential for the removal of toxic matters from wastewaters. In the present study, the titanium dioxide and titanium dioxide/zinc oxide (TiO2/ZnO) nanofibers prepared by electrospinning technique were coated on the sewage sludge carbon (SSC) surface for adsorption of Ni(II), Cu(II), and COD from aqueous solutions and industrial wastewaters of Iran. The synthesized adsorbents were characterized using XRD, SEM and EDX analysis. The effect of adsorbent type, pH, adsorbent dosage, contact time and initial concentrations of Ni(II), Cu(II) and COD on the adsorption capacity of synthesized SSC/TiO2 and SSC/TiO2/ZnO nanofibrous adsorbents... 

The nanofibers prepared by electrospinning process have high potential for the removal of toxic matters from wastewaters. In the present study, the titanium dioxide and titanium dioxide/zinc oxide (TiO2/ZnO) nanofibers prepared by electrospinning technique were coated on the sewage sludge carbon (SSC) surface for adsorption of Ni(II), Cu(II), and COD from aqueous solutions and industrial wastewaters of Iran. The synthesized adsorbents were characterized using XRD, SEM and EDX analysis. The effect of adsorbent type, pH, adsorbent dosage, contact time and initial concentrations of Ni(II), Cu(II) and COD on the adsorption capacity of synthesized SSC/TiO2 and SSC/TiO2/ZnO nanofibrous adsorbents... 

With the development of science and technology through social networks, the process of diffusion has become a controversial subject. In social networks, the process of diffusion is transmitted from one individual to another. The influence maximization problem, in which at least k nodes are chosen as the initial nodes of the spreader in the smallest amount of time, is one of the most critical aspects of the diffusion process. Furthermore, the initial nodes in the social network should generate the most influence on the other nodes in the network. However, in the algorithms proposed to solve the problem of influence maximization, the real-world factors which affect the influence probability in... 

Temporal and spatial analysis of dynamics of hybrid transversely excited atmospheric pressure (TEA)-CO2 lasers is studied using two different models with four and eight energy levels. These models are used for simulation of the laser and computing the output energy. Effects of several parameters such as input energies and gas mixture concentrations (especially presence of CO molecules) are also studied. © 2007 Elsevier Ltd. All rights reserved  

Machine learning (ML) algorithms are becoming popular in cosmology for extracting valuable information from cosmological data. In this paper, we evaluate the performance of a convolutional neural network (CNN) trained on matter density snapshots to distinguish clustering dark energy (DE) from the cosmological constant scenario and to detect the speed of sound (cs) associated with clustering DE. We compare the CNN results with those from a Random Forest (RF) algorithm trained on power spectra. Varying the DE equation of state parameter wDE within the range of -0.7 to -0.99 while keeping c2s = 1, we find that the CNN approach results in a significant improvement in accuracy over the RF... 

Effect of different conditions on shear behaviour of rock has been investigated by various researchers. As known, in larger scale the continuity of the rock material is interrupted by separated planes such as bedding planes, faults, shear zones, closure and the behaviour converts to be inelastic and anisotropic. Generally, discontinuities appear repeatedly in more than one preferential direction, creating a three dimensional structure, reducing its stiffness and shear strength as mechanical effects and increasing its transport velocity associated with discontinuity flow as hydraulic effects. They also make rock behavior more complex and different compared to the behavior of soil. According... 

Dynamic properties of soil, such as shear modulus and damping ratio, are necessary for analyzing the dynamic response of the soil in geostructures. This study investigates the effects of partially inherent anisotropy and stress-induced anisotropy on the shear stiffness of unsaturated soil through a series of dynamic hollow cylinder tests at medium strain levels. The different inherent anisotropy in tested sand specimens was introduced through different compaction water contents in the sample preparation stage while keeping the void ratio nearly constant. Moreover, the influences of the angle of maximum principal stress, α, and intermediate principal stress parameter, b = (σ2 − σ3)/(σ1 − σ3),... 

The cosmological constant term can be seen as a constant potential for a (scalar) field. In this viewpoint, at late times, the field is stopped rolling and behaves as a cosmological constant (w=-1). While at the early Universe, its kinetic term can be dominant and behaves as a stiff fluid (w=+1). This new phase lowers the cosmological sound horizon by increasing the Hubble parameter for very high redshifts. Consequently, the lower cosmological sound horizon results in the higher Hubble constant at the present time. This early phase ends before the photon decoupling, so we do not expect any new physics after the last scattering surface. We checked this model in the presence of (reduced) CMB,... 

This letter investigates the deterministic design of pilot power and pattern for sparse channel estimation in OFDM systems based on minimizing the coherence of the DFT sub-matrix. It has been suggested that the pilot pattern forming a cyclic difference set (CDS) or almost difference set (ADS) is optimal. So, we proposed a deterministic procedure that jointly optimized for pattern and power of pilots as a solution. First, pilot patterns forming CDS/ADS were gathered through a search. Then, the power was numerically allocated to the different pilots from all the patterns. Finally, the pilot pattern and power pair leading to minimum coherence was selected from the available pairs. Simulation... 

In this paper, the problem of finding the shortest path between two points in the presence of single-point visibility constraints is studied, In these types of constraint, there should be at least one point on the output path from which a fixed viewpoint is visible. The problem is studied in various domains, including simple polygons, polygonal domains and polyhedral surfaces. The method is based on partitioning the boundary of the visibility region of the viewpoint into a number of intervals. This is done from the combinatorial structure of the shortest paths from the source and destination to the points on the boundary. The result for the case of simple polygons is optimal with O(n) time... 

In this paper, we study the problem of finding the shortest path between two points inside a simple polygon such that there is at least one point on the path from which a query point is visible. We provide an algorithm which preprocesses the input in O (n2 + n K) time and space and provides logarithmic query time. The input polygon has n vertices and K is a parameter dependent on the input polygon which is O (n2) in the worst case but is much smaller for most polygons. The preprocessing algorithm sweeps an angular interval around every reflex vertex of the polygon to store the optimal contact points between the shortest paths and the windows separating the visibility polygons of the query... 

We study a constrained version of the shortest path problem in polygonal domains, in which the path must visit a given target polygon. We provide an efficient algorithm for this problem based on the wavefront propagation method and also present a method to construct a subdivision of the domain to efficiently answer queries to retrieve the constrained shortest paths from a single-source to the query point. © 2008 Springer-Verlag Berlin Heidelberg  

We study a constrained version of the shortest path problem in simple polygons, in which the path must visit a given target polygon. We provide a worst-case optimal algorithm for this problem and also present a method to construct a subdivision of the simple polygon to efficiently answer queries to retrieve the shortest polygon-meeting paths from a single-source to the query point. The algorithms are linear, both in time and space, in terms of the complexity of the two polygons. © 2004 Elsevier B.V. All rights reserved  

Computing the period of the periodic functions is the main reason of using Simon’s algorithm to attack symmetric-key cryptographic primitives. However, if the target function does not satisfy Simon’s promise completely or if the number of superposition queries of the adversary is limited, Simon’s algorithm cannot compute the actual target period, unambiguously. These problems may lead to the failure of period-finding-based quantum attacks.Our main aim in this paper is to relax Simon’s algorithm so that quantum adversaries can still carry out the mentioned attacks without any assumptions (Simon’s promise) on the target function. To that end, we use two different methods, each of which is...