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Bacterial chemotaxis can enhance the bioremediation of contaminants in aqueous and subsurface environments if the contaminant is a chemoattractant that the bacteria degrade. The process can be promoted by traveling bands of chemotactic bacteria that form due to metabolism-generated gradients in chemoattractant concentration. We developed a multiple-relaxation-time (MRT) lattice-Boltzmann method (LBM) to model chemotaxis, because LBMs are well suited to model reactive transport in the complex geometries that are typical for subsurface porous media. This MRT-LBM can attain a better numerical stability than its corresponding single-relaxation-time LBM. We performed simulations to investigate the effects of substrate diffusion, initial bacterial concentration, and hydrodynamic dispersion on the formation, shape, and propagation of bacterial bands. Band formation requires a sufficiently high initial number of bacteria and a small substrate diffusion coefficient. Uniform flow does not affect the bands while shear flow does. Bacterial bands can move both upstream and downstream when the flow velocity is small. However, the bands disappear once the velocity becomes too large due to hydrodynamic dispersion. Generally bands can only be observed if the dimensionless ratio between the chemotactic sensitivity coefficient and the effective diffusion coefficient of the bacteria exceeds a critical value, that is, when the biased movement due to chemotaxis overcomes the diffusion-like movement due to the random motility and hydrodynamic dispersion.

Traveling bacterial waves are capable of improving contaminant remediation in the subsurface. It is fairly well understood how bacterial chemotaxis and growth separately affect the formation and propagation of such waves. However, their interaction is not well understood. We therefore perform a modeling study to investigate the coupled effects of chemotaxis and growth on bacterial migration, and examine their effects on contaminant remediation. We study the waves by using different initial electron acceptor concentrations for different bacteria and substrate systems. Three types of traveling waves can occur: a chemotactic wave due to the biased movement of chemotactic bacteria resulting from metabolism-generated substrate concentration gradients; a growth/decay/motility wave due to a dynamic equilibrium between bacterial growth, decay and random motility; and an integrated wave due to the interaction between bacterial chemotaxis and growth. Chemotaxis hardly enhances the bacterial propagation if it is too weak to form a chemotactic wave or its wave speed is less than half of the growth/decay/motility wave speed. However, chemotaxis significantly accelerates bacterial propagation once its wave speed exceeds the growth/decay/motility wave speed. When convection occurs, it speeds up the growth/decay/motility wave but slows down or even eliminates the chemotactic wave due to the dispersion. Bacterial survival proves particularly important for bacterial propagation. Therefore we develop a conceptual model to estimate the speed of growth/decay/motility waves.

Organic shale in coal-bearing strata contains a large amount of shale gas resource in China. The organic shale is typically interlayered with coal beds and tight sandstone, and thus, joint development of the three unconventional gases, coal bed methane, tight gas, and shale gas, is becoming a frontier topic. In this paper, an integrated characterization of coal-bearing shale was implemented through a systematic series of measurements to assess the potential of shale gas in the Huainan–Huaibei coalfield. According to X-ray diffraction, quartz, kaolinite, and mixed illite/smectite (I/S) are the major minerals and the brittleness index for most samples is low to moderate (30–60). The risk of water swelling during hydraulic stimulation may be low in terms of the low concentration of smectite and mixed I/S. The efficiency of acid solution is limited by the low concentration of calcite and dolomite. The pore system has been well-developed on the basis of the thin section, scanning electron microscopy, mercury i...

The depositional environment of organic-rich shale and the related tectonic evolution in China are rather different from those in North America. In China, organic-rich shale is not only deposited in marine environment, but also in non-marine environment: marine-continental transitional environment and lacustrine environment. Through analyzing large amount of outcrops and well cores, the geologic features of organic-rich shale, including mineral composition, organic matter richness and type, and lithology stratigraphy, were analyzed, indicating very special characteristics. Meanwhile, the more complex and active tectonic movements in China lead to strong deformation and erosion of organic-rich shale, well-development of fractures and faults, and higher thermal maturity and serious heterogeneity. Co-existence of shale gas, tight sand gas, and coal bed methane (CBM) proposes a new topic: whether it is possible to co-produce these gases to reduce cost. Based on the geologic features, the primary production issues of shale gas in China were discussed with suggestions.

The corrosion fatigue behavior of epoxy-coated Mg–3Al–1Zn alloy was investigated in air and 3.5 wt% NaCl solution. Epoxy coating as a new method was used to improve the corrosion fatigue property of the material. Results show that the fatigue limit (FL) of the coated specimens is higher than that of the uncoated specimens in 3.5 wt% NaCl solution because of the strengthening and blocking functions of the epoxy coating. The FL of the coated specimens in 3.5 wt% NaCl solution is as high as that in air. It implies that the coated specimens are not as sensitive to the environment as the magnesium alloy. The low tensile strength and the short elongation of the pure epoxy coating lead to that the fatigue crack of the coated specimen is always initiated from the epoxy-coating film. Pores and pinholes accelerate the fatigue crack initiation process. Pinholes are caused by the corrosion reactions between the epoxy coating and the NaCl solution.

The superficial temperature evolution of 10 mm-thick extruded AZ31B magnesium alloy plate was measured during the high-cycle fatigue test. The mechanism of heat generation was analyzed according to the law of energy conversion. The temperature fluctuation during the fatigue test was related to the cyclic hardening/softening process which was discussed according to the followed tensile tests. The temperature evolution was also measured during tensile tests. The influence of cyclic hardening/softening process on the change of thermoelastic effect in tensile tests was also discussed. Finally, the density evolution of dislocation was related to the energy change during fatigue tests.

The fatigue behavior of AZ31B magnesium alloy welded joint during high cycle fatigue test was investigated by infrared thermography. Five stages of superficial temperature evolution were observed: an initial temperature increase, a temperature decline, a temperature equilibrium, an abrupt temperature increase and a temperature drop after the failure. The theoretical models were formulated to explain the observed temperature evolution. The mean temperature decline caused by thermoelastic effect was observed and discussed when the maximum stresses were below 30 MPa. The influence of weld reinforcement on fatigue behavior was also investigated. A good precision was achieved in fatigue strength prediction by means of infrared thermography.

Based on the infrared thermography method, experiments are carried out to investigate the evolution of temperature field of the extruded AZ31B magnesium alloy specimens under high cyclic fatigue load. The experimental results show that the superficial temperature of specimen under cyclic fatigue load changes with the number of cycles. According to the characteristics of surface temperature change, we propose a formula to calculate the residual fatigue life using energy approach. The proposed formula to assess the fatigue parameters (fatigue limit, residual fatigue life, fatigue life and S–N curve) achieves good results for AZ31B magnesium alloy. Furthermore, the fatigue limits (ΔσeSN = 90·3 MPa) derived from the traditional method through 107 cycles were compared with the values predicted by the infrared thermographic method (ΔσeTM = 87·3 MPa) and the energy approach (ΔσeΦ = 86·2 MPa), and the comparison results of percentage differences are 3·3 and 4·5% respectively.

The adsorption of NH 3 on the Lewis and Bronsted acid sites of MoO 3 (0 1 0) surface has been investigated based on the density functional theory (DFT) method using the clusters models. The calculated results indicate that NH 3 could strongly adsorb on both the Lewis and Bronsted acid sites in the form of NH 3 species and NH 4 + respectively, whereas the adsorption on the Lewis acid site is found to be more favorable energetically than that on the Bronsted acid site. For the Lewis acid site Mulliken population analysis shows a donation of lone pairs from NH 3 to the surface and activation of N–H bond. The overlaps of N-s, N-p and Mo-d orbitals suggest the strong interaction between N and Mo atoms. For the Bronsted acid site N–H bond is also activated by the formation of NH 4 + species. The hybridizations between H and O atoms as well as N and H atoms are the major reasons for strong chemical adsorption of NH 3 and the existence of NH 4 + species, which partly attributed to the presence of N–H… O hydrogen bonds. Furthermore, the formation of a second Lewis acid site at adjacent or diagonal site results in slight changes of adsorption stability, structural changes and charge redistributions, suggesting its small influence on NH 3 adsorption.

The surface temperature of extruded AZ31B alloy plate was measured by infrared thermograph in air during tension and high-cycle fatigue tests. The mechanism of heat production was discussed and the value of critical fatigue damage temperature was calculated according to the P —Δ T curve. Results show that the variation trend of temperature is different between tension and fatigue tests. The temperature evolution in tension test consists of four stages: linear decrease, reverse linear increase, abrupt increase, and final drop. The initial decrease of temperature is caused by thermal elastic effect, which is corresponding to the elastic deformation in tension progress. When cyclic loading is above the fatigue limit, the temperature evolution mainly undergoes five stages: initial increase, steep reduction, steady state, abrupt increase, and final drop. The peak temperature in fatigue test is caused by strain hardening that can be used to evaluate the fatigue life of magnesium alloy. The critical temperature variation that causes the fatigue failure is 3.63 K. When Δ T ≤3.63 K, the material is safe under cyclic loading. When Δ T >3.63 K, the fatigue life is determined by cycle index and peak temperature.

Shallow wake patterns are investigated by numerical method based on the solutions of two-dimensional (2D) shallow water equations and three-dimensional (3D) Reynolds-Averaged Navier-Stokes (RANS) equations with the implicit scheme on collocated mesh in the FVM framework. The analysis are made on vorticity contour distribution, transverse velocity (uy) variation with time, Strouhal number (St) and time-averaged longitudinal velocity (ux) to verify the characteristics of shallow wakes behind cylinder. We compare the numerical results with Chen’s experiment very well and show the capability and difference of 2D model and 3D model in modeling shallow wake structure. The results show that the 2D model predicts the vortex street (VS) wake well, yet the 3D model is fit for the steady bubble (SB) wake. The 2D model performs more accurately when VS wake transforms to unsteady bubble (UB) wake, while the 3D model is better when UB wake transforms to SB wake.

Density functional theory (DFT) cluster studies on the MoO 3 (0 1 0) surface are carried out to examine formation of different locations of terminal oxygen vacancies and adsorption of NO in this work. The formation of two adjacent terminal oxygen vacancies requires almost twice energy of formation of one terminal oxygen vacancy, and the formation of two adjacent terminal oxygen vacancies is slightly easier than that of two diagonal terminal oxygen vacancies. NO can only adsorb on the cluster holding terminal oxygen vacancy and preferentially occupies the terminal oxygen vacancy site with N bonds to the surface. The increase of N–O bond length and the decrease of N–O bond order before and after NO adsorption indicate that one terminal oxygen vacancy can improve the activation of NO. The presence of another surrounding terminal oxygen vacancy further promotes the adsorption ability and the activation of NO.

To apply robotic surgery of early ovarian malignancy tumors clinically and evaluate its feasibility in management for early ovarian cancer.Using the da Vinci robotic surgical system, seven patients with early ovarian malignancy tumors (stage I) underwent robotic surgery from April 2012 to September 2013. The average age was 45.7 years. Robotic surgeries approaches contained salpingo-oophorectomy, para-aortic lymphadenectomy, pelvic lymphadenectomy, omentectomy and appendectomy. Perioperative and follow-up clinical data were recorded.All robotic surgeries were successfully completed without the conversion to laparotomy. The mean operative time was 225 minutes (100-330 minutes). The average estimated blood loss was 171 ml (20-600 ml). No patients received blood transfusions. No intraoperative and postoperative complications were observed. The average number of pelvic lymph node dissected were 18.3 (11-34). The average number of para-aortic lymph node dissected were 3.7 (3-4). The mean follow-up time was 26.0 months after surgery (20-36 months). Currently, all patients had no tumor recurrence and survived.Robotic surgery is feasible as a novel alternative approach in the treatment of early ovarian malignancy tumors.

The fatigue crack propagation rate of as-extruded AZ31B magnesium alloy was studied. Compact tension [C(T)] of the notch direction parallel (T-L), vertical (L-T), and inclined at 45° to the extrusion direction was investigated. The experimental results indicate that the crack propagation direction is parallel to the extrusion direction for T-L and L-T specimens, whereas the specimen inclined at 45° has an angular deflection of 9° to 11° toward the extrusion direction. The T-L specimen has the fastest fatigue crack propagation rate, and the L-T specimen has the slowest rate, the fatigue crack propagation rate of the specimen inclined at 45° is between the two directions. The crack tip propagates by both transgranular and intergranular fractures. Fatigue fractures consist of cleavage plane or quasi-cleavage and are brittle fractures. The fatigue striation occurs for specimens inclined at 45° and its size is 3–15 μm.

Four and a half LIM domain (FHL) protein 3 is a member of the FHL protein family that plays roles in the regulation of signal transduction, cell adhesion, survival, and mobility. FHL3 has been implicated in the development and progression of liver cancer. However, the biological function of FHL3 in other cancers remains unclear. Here, we show that FHL3 is downregulated in breast cancer patients. Using small interfering RNA (siRNA) knockdown and/or overexpression experiments, we demonstrated that FHL3 suppressed anchorage-dependent and -independent growth of human breast cancer cells. The antiproliferative effects of FHL3 on breast cancer cell growth were associated with both the G1 and the G2/M cell cycle arrest, which was accompanied by a marked inhibition of the G1-phase marker cyclin D1 and the G2/M-phase marker cyclin B1 as well as the induction of the cyclin dependent kinase inhibitor p21 (WAF1/CIP1), a negative regulator of cell cycle progression at G1 and G2. These results suggest that FHL3 may play a role in the development and progression of breast cancer, and thereby may be a potential target for human breast cancer gene therapy. © 2011 IUBMB IUBMB Life, 63(9): 764–771, 2011

The dissolved oxygen concentration in a flow changes with distance downstream of the spillway crest and depends on the geometric configuration of the spillway and the hydraulic and operating conditions. A mathematical model was developed to simulate the turbulent structure of the flow over the spillway of the Three Gorges Dam at the 145 m reservoir water level to study the aeration characteristics and the gas transport. The model was calibrated and verified with measured data. The analysis of distribution of the aeration and the dissolved oxygen showed that the downstream water level, upstream dissolved oxygen content, and the flow discharge all affect the dissolved oxygen saturation downstream of the sluicing dam. The simulation provides guidance for controlling the dissolved oxygen supersaturation and environmentally friendly operation of the Three Gorges Dam.

A generic numerical model which is valid both in the strong inversion regime and sub-threshold regime for the detection of terahertz radiation utilizing Metal–Oxide–Semiconductor (MOS) Field-Effect Transistors (FETs) is developed in this paper. A general carrier density equation and gate leakage current are coupled to the basic hydrodynamic equations which govern the electron transport in the 2D channel of the MOS field-effect transistor to obtain the numerical solution; a progress-based photo-response signal of the terahertz radiation of MOSFET is calculated. The simulation results are compared with existing analytical results, proving the validity of the proposed numerical model and overcoming limitations of the analytical theories.

Laser welding has been considered to be one of the most promising joining processes for Nitinol medical device manufacturing. Presently, there is still a limited understanding about how laser welding affects the microstructure and the resultant corrosion behaviors. This work aimed to reveal the microstructural factors that influence the corrosion resistance of laser-welded crossed Nitinol joints. The microstructures within various zones of the joints were characterized by using transmission electron microscopy (TEM), and the corrosion behaviors of the joints in 0.9% NaCl and Hank’s solutions were studied. The base metal exhibits a single austenite (B2) phase and the highest corrosion resistance. The phase constituent of the fusion zone is the coexistence of the B2 matrix and some precipitates (T2Ni, TiNi3, and Ti3Ni4 particles), resulting in a slight decrease in corrosion resistance. The heat affected zone (HAZ) shows the austenite matrix but with the precipitation of R-phase, which considerably reduces the corrosion potential, making it the weakest zone.

In this paper, studies were conducted to investigate the deformation behavior and microstructure change in a hot-rolled AZ31B magnesium alloy during a tensile-tensile cyclic loading. The relationship between ratcheting effect and microstructure change was discussed. The ratcheting effect in the material during current tensile-tensile fatigue loading exceeds the material’s fatigue limit and the development of ratcheting strain in the material experienced three stages: initial sharp increase stage (Stage I); steady stage (Stage II); and final abrupt increase stage (Stage III). Microstructure changes in Stage I and Stage II are mainly caused by activation of basal slip system. The Extra Geometrically Necessary Dislocations (GNDs) were also calculated to discuss the relationship between the dislocation caused by the basal slip system and the ratcheting strain during the cyclic loading. In Stage III, both the basal slip and the {11−20} twins are found active during the crack propagation. The fatigue crack initiation in the AZ31B magnesium alloy is found due to the basal slip and the {11−20} tensile twins.

Summary Aerobic glycolysis (the Warburg effect) facilitates tumor growth, and drugs targeting aerobic glycolysis are being developed. However, how the Warburg effect is directly regulated is largely unknown. Here we show that transcription factor SIX1 directly increases the expression of many glycolytic genes, promoting the Warburg effect and tumor growth in vitro and in vivo . SIX1 regulates glycolysis through HBO1 and AIB1 histone acetyltransferases. Cancer-related SIX1 mutation increases its ability to promote aerobic glycolysis and tumor growth. SIX1 glycolytic function is directly repressed by microRNA-548a-3p, which is downregulated, inversely correlates with SIX1, and is a good predictor of prognosis in breast cancer patients. Thus, the microRNA-548a-3p/SIX1 axis strongly links aerobic glycolysis to carcinogenesis and may become a promising cancer therapeutic target.

Failure in early diagnosis and ineffective treatment are the major causes of ovarian cancer mortality. Hyaluronan and its receptor, cluster of differentiation (CD)44, have been considered to be valid targets for treating cancer. The anti-CD44 monoclonal antibody IM7 is effective in treating ovarian cancer; however, its toxicity should not be ignored. The present study has developed a new drug carrier system composed of chitosan nano-particles coated with polylactic acid (PLA) to improve the treatment efficacy and reduce toxicity. An ionic crosslinking method and 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride/N-hydroxysuccinimide were used to prepare the IM7 antibody, which was loaded with chitosan nano-particles. The surfaces of the nano-particles were coated with PLA to generate PLA-chitosan-IM7. Subsequently, transmission electron microscopy (TEM) was used to observe the size and zeta potential of the nano-particles. In addition, a spectrophotometer was used to calculate the loading rate and release rate of the nano-particles in acidic and neutral environments. MTT assay was used to evaluate the anti-proliferative effect of PLA-chitosan-IM7 on the human ovarian cancer cell line HO-8910PM. In addition, an in vivo imaging system was used to further investigate the effect of PLA-chitosan-IM7 on the treatment of mice with ovarian cancer. A total of 35 days subsequent to PLA-chitosan-IM7 treatment, all animals were sacrificed by CO2, and the tumors were removed and weighted. The PLA-chitosan-IM7 nano-particles were successfully prepared, since TEM revealed that their size was 300-400 nm and their zeta potential was +25 mV. According to the spectrophotometry results, the loading rate was 52%, and PLA-chitosan-IM7 exhibited good resistance to acids. MTT assay demonstrated that PLA-chitosan-IM7 could suppress the proliferation of HO-8910PM cells in vitro. The in vivo imaging system revealed that PLA-chitosan-IM7 was effective in controlling the development of human ovarian cancer cells and the tumor weight. These results suggest that PLA-chitosan-IM7 could be effective in treating cancers in vitro and in vivo, which may provide a novel approach to enhance the effectiveness of anti-CD44 treatment while reducing its toxicity.

Certificateless public key cryptography is a new paradigm with two interesting features. On one hand, it keeps the certificate free property of identity-based public key cryptography (ID-PKC), while on the other hand, it gets rid of the inherent key escrow problem of ID-PKC. These two distinctive features make certificateless threshold signature schemes more applicable in practice as it removes the cost of transmitting and verifying the public key certificates of the participants who are involved in signing, and yet without the fear of key escrow. In this paper, we analyze the security of an existing certificateless threshold signature (CLTHS) scheme recently proposed by Zhong et al.[26]. We show it is insure by demonstrating its three security drawbacks. Especially, we present a kind of public key replacement attack against it. Our attack reveals that it is subject to universal forgeries of type I adversaries

Four and a half LIM domain (FHL) protein 3 is a member of the FHL protein family that plays roles in the regulation of signal transduction, cell adhesion, survival, and mobility. FHL3 has been implicated in the development and progression of liver cancer. However, the biological function of FHL3 in other cancers remains unclear. Here, we show that FHL3 is downregulated in breast cancer patients. Using small interfering RNA (siRNA) knockdown and/or overexpression experiments, we demonstrated that FHL3 suppressed anchorage-dependent and -independent growth of human breast cancer cells. The antiproliferative effects of FHL3 on breast cancer cell growth were associated with both the G1 and the G2/M cell cycle arrest, which was accompanied by a marked inhibition of the G1-phase marker cyclin D1 and the G2/M-phase marker cyclin B1 as well as the induction of the cyclin dependent kinase inhibitor p21 (WAF1/CIP1), a negative regulator of cell cycle progression at G1 and G2. These results suggest that FHL3 may play a role in the development and progression of breast cancer, and thereby may be a potential target for human breast cancer gene therapy.

Background Innate immunity to viruses involves receptors such as RIG-I, which senses viral RNA and triggers an IFN-β signaling pathway involving the outer mitochondrial membrane protein MAVS. However, the functional status of MAVS phosphorylation remains elusive. Methodology/Principal Findings Here we demonstrate for the first time that MAVS undergoes extensive tyrosine phosphorylation upon viral infection, indicating that MAVS phosphorylation might play an important role in MAVS function. A tyrosine-scanning mutational analysis revealed that MAVS tyrosine-9 (Y9) is a phosphorylation site that is required for IFN-β signaling. Indeed, MAVS Y9F mutation severely impaired TRAF3/TRAF6 recruitment and displayed decreased tyrosine phosphorylation in response to VSV infection compared to wild type MAVS. Functionally, MAVS Y9 phosphorylation contributed to MAVS antiviral function without interfering with its apoptosis property. Conclusions/Significance These experiments identify a novel residue of MAVS that is crucially involved in the recruitment of TRAF3/TRAF6 and in downstream propagation of MAVS signaling.

Background The calcification of blood vessels correlates with increased morbidity and mortality in patients with atherosclerosis, diabetes, and end-stage kidney disease. Increased inflammasome activation has been shown to play an important role in the pathogenesis of atherosclerosis. However, the contribution of inflammasome activation on the development of vascular calcification has not been investigated. Methods β-Glycerophosphate (β-GP) was used as a procedure to induce extensive artery calcification in primary vascular smooth muscle cells (VSMCs). Analysis of the levels of Nalp3 inflammasome complex was performed by quantitative real-time PCR and western blotting. The effect of Nalp3 deficiency on VSMC calcification was examined after transfecting Nalp3 siRNA into cultured VSMCs. Results We demonstrated for the first time that the mRNA levels of Nalp3 inflammasome complex including Nalp3, ASC and caspase1 were upregulated in calcifying VSMCs, resulting in increased IL-1β secretion. Inhibition of inflammasome activation by Nalp3 RNA interference reduced IL-1β secretion and inhibited VSMC calcification. Further analysis of clinical popliteal artery specimens showed an upregulation of inflammasome complex mRNA levels (4/5) and caspase1 activity (5/5) compared with their non-calcified adjacent tissues, indicating that Nalp3 inflammasome was tightly correlated with arterial calcification disease. Conclusion Our findings indicate that activation of the Nalp3-mediated inflammatory response pathway is an important venue associated with host response and pathogenesis of VSMC calcification.

Different mechanisms of deformation could make different influence on inner structure and physical properties of tectonically deformed coal (TDC) reservoirs. This paper discusses the relationship between macromolecular structure and physical properties of the Huaibei-Huainan coal mine areas in southern North China. The macromolecular structure and pore characteristics are systematically investigated by using techniques such as X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), electron paramagnetic resonance (EPR), nuclear magnetic resonance (NMR), and low-temperature nitrogen adsorption method. The results suggest that under the directional stress, basic structural units (BSU) arrangement is closer, and the orientation becomes stronger from brittle deformed coal to ductile deformed coal. Structural deformation directly influences the macromolecular structure of coal, which results in changes of pore structure. The nanoscale pores of the cataclastic coal structure caused by the brittle deformation are mainly mesopores, and the proportion of mesopores volume in ductile deformed coal diminishes rapidly. So the exploration and development potential of coalbed gas are good in reservoirs such as schistose structure coal, mortar structure coal and cataclastic structure coal. It also holds promise for a certain degree of brittle deformation and wrinkle structure coal of low ductile deformation or later superimposed by brittle deformation.

Modeling of resonant detection of terahertz (THz) radiation of Metal-Oxide-Semiconductor (MOS) field effect transistors (FETs) under the optical beating mode is studied in this paper. An analytical model is first proposed which covers all operation regions of FETs from sub-threshold to the strong inversion, and then is verified by the numerical tool which has been improved to simulate THz detection characteristics under the case of optical beating. Furthermore, extensive characteristics of resonant detection under the optical beating mode have been predicted.

Terahertz (THZ) detection by field effect transistors (FETs) has been paid great attention in recent years. This paper outlined the numerical study of terahertz radiation detection by FETs in our group, including the fundamental THz detection model, detection model with two sources, heterodyne detection model and optical beating model. These study results demonstrated the potential application of MOSFETs as THz detectors, which may be helpful in the optimization of MOSFET in improving THZ detector performance.

The heterodyne detection characteristics of field effect transistors are studied in this paper. Based on the hydrodynamic equations which govern the terahertz signal transport in field effect MOS transistors, a numerical simulation program is developed. This program works well in all operation regions of FETs from sub-threshold to strong inversion and from linear to saturation. The work demonstrates the potential to use MOS transistors for THz detectors and the method to optimize the device structure. Simulation results agree well with the existing theory in the nonresonant situations.

A numerical method is proposed to simulate the corresponding terahertz photoresponse which is induced by radiations between source-and-gate and gate-and-drain electrodes in field effect transistors. Simulations illustrate that the response of terahertz radiation in field effect transistor depends on the gate bias. The response contains contributions of different polarities which induced by radiations between 'source and gate electrodes' and 'gate and drain electrodes' respectively. The simulation matches well with the existing theory quantitatively. The proposed method is also used to study the response in resonant region by changing some parameters of field effect transistors (FET). The results illustrate that it is a useful tool in THz detector design and optimization.