Sharif Digital Repository

Central composite orthogonal design was applied to quantify relations of xylanase production, loss of dry matter and change of pH with four critical variables during solid state fermentation of a mixture of wheat bran and wheat straw on which Aspergillus niger CCUG 33991 was cultivated. The studied variables included the percentage of wheat straw, wheat bran, temperature, moisture content, and fermentation time. The second-order quadratic model predicted the xylanase activity at a suitable set of conditions namely 29°C, 55% moisture content, and 50 hours of fermentation to be 1465 U/g of fermented dry matter which differed less than 6% from measured value at this set of conditions.... 

The performance of continuous solid state bioreactors having two different solid substrate flow patterns, namely plug flow and completely mixed flow, is quantified for both steady-state and transient operation using a simple mathematical model. The core assumption is that each substrate particle acts as an infinitesimal bioreactor. The residence time distribution of the particles is considered in the formulation of the equations for the mixed-flow bioreactor and the error that results from neglecting it is investigated by comparing the simulation results with those of a completely mixed, continuous bioreactor for submerged liquid fermentation (a chemostat). The model is extended to include... 

We develop a method for predicting the moisture content of the fermenting solids in an intermittently mixed packed-bed bioreactor on the basis of measurements of the inlet and outlet gas stream temperatures and the assumption that both the gas streams are saturated with water vapor. This method can be used to estimate when an intermittently mixed packed bed should be mixed and how much water should be added during the mixing event. The predictions were experimentally verified for the growth of Aspergillus niger on wheat bran in a thin packed bed. We show that the application of a controller based on our estimation method would have led to adequate moisture control, with significant errors in... 

A mathematical model was introduced to describe the heat transfer behaviour of moist wheat bran beds. Comparison of predicted transient temperature profiles with experimental data collected in a simulated bed was used to evaluate bed thermal conductivity at various conditions. This parameter was correlated with the bed density and moisture content via a mathematical relation. Furthermore, extent of error in thermal conductivity evaluation resulted from neglecting water vapour diffusion was quantified. Results provide useful means to design, analyse, and predict the behaviour of solid state fermenters in a more reliable manner. © 2005 Institution of Chemical Engineers  

The effect of wall cooling in tray-type solid-state fermenters was investigated by cultivation of Aspergillus niger ATCC 10 864 on wheat bran. Temperature, moisture, pH and glucoamylase activity in the bed were monitored. Application of the heat exchanger plate reduced the overall water loss but increased the heterogeneity of moisture distribution in the bed. Moisture content increased markedly close to the heat transfer plate while the upper regions of the bed dried out. The thermal conductivity of the bed was measured to be 0.19 Wm-1 K-1. At these conditions and depending on the air flow rate, 58-82% of the metabolic heat was removed via conduction towards the plate. A mathematical model... 

Using multiple antennas at the transmit and receive sides of a passive radar brings both the benefits of MIMO radar and passive radar. However one of the obstacles arisen in such configuration is the receive antennas placement in proper positions so that the radar performance is improved. Here we just consider the case of positioning one receiver among multiple illuminators of opportunity. Indeed it is a start for the solution of optimizing the geometry of the multiple receivers in a passive radar  

SbCl3 supported on montmorillonite K-10 is an efficient catalyst for the ring opening of epoxides with aromatic amines under solvent-free conditions and microwave irradiation to give the corresponding b-amino alcohols in high yields with high regioselectivity  

In this paper, we consider an integrated sensing and communication (ISAC) system with wireless power transfer (WPT) where an unmanned aerial vehicle (UAV)-based radar serves a group of energy-limited communication users in addition to its sensing functionality. In this architecture, the radar senses the environment in phase 1 (namely sensing phase) and mean-while, the communications users (nodes) harvest and store the energy from the radar transmit signal. The stored energy is then used for information transmission from the nodes to UAV in phase 2, i.e., uplink phase. Performance of the radar system depends on the transmit signal as well as the receive filter; the energy of the transmit... 

One of the important obstacles in MIMO (Multiple Input Multiple Output) radars is the issue of designing proper transmit signals. Indeed, the capability of signal design is a significant advantage in MIMO radars, through which, the system can achieve much better performance. Many different aspects of this performance improvement have been considered yet, and the transmit signals have been designed to attain such goal, e.g., getting higher SNR or better detector's performance at the receiver. However, an important tool for evaluating the radar's performance is its ambiguity function. In this paper, we consider the problem of transmit signal design, in order to optimize the ambiguity function... 

Two gains play key roles in recently developed MIMO wireless communication systems: "spatial diversity" gain and "spatial multiplexing" gain. The diversity gain refers to the capability to decrease the error rate of the MIMO channel, while the multiplexing gain implicitly refers to the amount of increase in the capacity of the MIMO channel. It has been shown that there is a fundamental tradeoff between these two types of gains, meaning interplay between increasing reliability (via an increase in the diversity gain) and increasing data rate (via an increase in the multiplexing gain). On the other hand, recently, MIMO radars have attracted much attention for their superior ability to enhance... 

It is a well known fact that using multiple antennas at transmit and receive sides improves the detection performance. However, in such multiple-input multiple-output (MIMO) configuration, proper positioning of transmitters and receivers is a big challenge that can have significant influence on the performance of the overall system. In addition, determining the power of each transmitter under a total power constraint is a problem that should be solved in order to enhance the performance and coverage of such a system. In this paper, we design the Neyman-Pearson detector under the Rayleigh scatter model and use it to introduce a criterion for the antenna placement at both transmit and receive... 

There has been much interest, recently, towards exploiting the Multiple-Input Multiple-Output (MIMO) technique in radar. It is shown that using multiple antennas at transmit and receive sides can improve the performance of the system. However, in order to analyze the system's performance, its ambiguity function, i.e. the ambiguity function of a MIMO radar, is needed to be defined. In this paper, beginning from the information theoretic definitions, we derive such function, specifically for a MIMO radar with widely separated antennas  

By combining the two ideas of MIMO (Multiple Input Multiple Output) and PCL (Passive Coherent Location) in radar, one can achieve the advantages of both recently developed techniques simultaneously. While using multiple antennas at the receive side provides a spatial diversity of the object to be detected, using multiple illuminators of opportunity, most importantly, makes the radar covert to the interceptors. One obstacle in such MIMO configuration is choosing the positions of the receive antennas. In this paper, after analyzing the Neyman-Pearson detector for the DVB-T based PCL, we introduce the probability of missed detection as a criterion to place the receive antenna. Here, we only... 

One of the most important obstacles in passive radar applications is removing the direct signal from the target channel. Otherwise, week echoes from the targets in the target channel would be ignored due to the limited dynamic range of the system. One of the most effective techniques in this field is using adaptive filters. In this paper various adaptive filters are introduced and their performances are shown and compared  

It has been shown that using multiple antennas in a radar system improves the performance considerably, since multiple target echoes are received from different aspect angles of the target. In this way, the target detection is improved. However, when using multiple antennas, some problems, such as designing the transmit signals, synchronization, etc. emerge that should be solved. One of such problems is the receiver placement. Receiver placement deals with choosing a proper position for the receive antenna in order to optimize the whole system's performance. In this paper, a receiver placement procedure based on improving the radar ambiguity function is proposed for the case of a multisite... 

By employing the MIMO (multiple-input-multiple-output) technology in radar, some new problems emerged, that, in order to benefit the MIMO gains in radar, it was necessary to solve them suitably. One of such obstacles is determining the positions of receive antennas in a MIMO radar system with widely separated antennas (WS MIMO radar), since it is shown that the antennas' positions affect the whole system's performance considerably. In this study, a proper receivers' positioning procedure is proposed. To do this end, four criteria are developed based on the proposed MIMO detector and the MIMO ambiguity function. The simulations verify that the proposed positioning procedure improves the... 

Phenols and alcohols are silylated with hexamethyldisilazane (HMDS) under microwave irradiation in solvent-free condition in good to excellent yields  

Modified couple stress theory is a size-dependent theorem capturing the micro/nanoscale effects influencing the mechanical behaviors of the micro- and nanostructures. In this paper, it is applied to investigate the nonlinear vibration of carbon nanotubes under step DC voltage. The vibration, natural frequencies and dynamic pull-in characteristics of the carbon nanotubes are studied in detail. Moreover, the effects of various boundary conditions and geometries are scrutinized on the dynamic characteristics. The results reveal that application of this theory leads to the higher values of the natural frequencies and dynamic pull-in voltages  

We study a classical problem in communication and wireless networks called Finding White Space Regions. In this problem, we are given a set of antennas (points) some of which are noisy (black) and the rest are working fine (white). The goal is to find a set of convex hulls with maximum total area that cover all white points and exclude all black points. In other words, these convex hulls make it safe for white antennas to communicate with each other without any interference with black antennas. We study the problem on three different settings (based on overlapping between different convex hulls) and find hardness results and good approximation algorithms  

Hybrid nanofluids have several advantages compared with the conventional types due to their modified properties. Their enhanced thermophysical and rheological properties make them more appropriate for solar energy systems. In this review paper, an overview of solar energy systems is represented, and afterwards, applications of hybrid nanofluids in various solar technologies, especially solar thermal, are reviewed. Comparison between the nanofluidic systems, and the conventional ones is performed in order to gain a deeper insight into the advantages of using nanofluids. According to the results of the reviewed studies, the most important reason for performance enhancement of nanofluidic solar...