Terminal Charges Research Articles

Compact Charge Model for Independent-Gate Asymmetric DGFET

Analytical expressions for terminal charges of an independent-gate asymmetric double gate MOSFET (DGFET) are derived. The new charge model is <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">∞</sub> continuous, valid for all bias conditions and does not involve charge-sheet approximation. This is accomplished by developing the symmetric linearization method in the form that does not require identical boundary conditions at the two Si-SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> interfaces and allows for the volume inversion in the DGFET channel. Verification of the model is performed with both numerical computations and 2D TCAD simulations under a wide range of biasing conditions. The terminal charges expressions are similar to those in the PSP bulk MOSFET model and in the PSP-based common-gate symmetric DGFET model. The latter becomes a special case of the new model.

Surface-potential-based compact modeling of dynamically depleted SOI MOSFETs

We present a complete surface-potential-based compact model of dynamically depleted (DD) SOI MOSFETs. The surface potential equation of DD-SOI MOSFETs was reconditioned to avoid the unphysical behaviors near the flat-band voltage. In order to capture the dynamic depletion effect, the coupling equation for the front and back surface potentials was reformulated to include the back gate effect, which is not available in other surface-potential-based DD-SOI compact models. The new formulation of surface potential and coupling equations was verified by comparing with numerical computations combining the Pao–Sah double integral based formulation and the exact coupling equation. To obtain explicit expressions for the terminal charges and drain current, a new symmetric linearization method has been proposed. The complete model, PSP-SOI DD is implemented in the context of the PSP and PSP-SOI PD models and includes all the secondary effects, floating body simulation capability, etc. The new model has been extensively verified with 2D TCAD simulation results and accurately captures the manifestation of the dynamic depletion effect observed in the device characteristics.

Analysing the optimal location of a hub port in Southeast Asia

This paper applies an integer programming model on the selection of the Pakbara port as an expecting hub competition among the major ports in Southeast Asia. By solving the integer programming model, several origin/destination container flows in the world are serviced via candidate hub ports such that the total system costs, taking into account port costs (entrance and terminal handling charges) and shipping costs (feeder and mainline) are minimised. The result shows the Port Klang or the Pakbara port as the optimal single-hub solution in several scenarios of structural shifts in traffic flows at the Pakbara port.

Effects of Terminal Functional Groups on the Stability of the Polyproline II Structure: A Combined Experimental and Theoretical Study

The conformational stability of the polyproline II (PPII) helix with respect to the functional groups at the C- and N-termini was examined both experimentally and theoretically. Oligoprolines AcN-[Pro](12)-CONH(2) (1), HN-[Pro](12)-CONH(2) (2), AcN-[Pro](12)-CO(2)H (3), and HN-[Pro](12)-CO(2)H (4) with charged and capped termini served as model compounds, and the relative ease with which they switch from the PPII to the polyproline I (PPI) helix was used as a measure to analyze their conformational stabilities. CD spectroscopic studies demonstrate that a positively charged N-terminus and a negatively charged C-terminus destabilize the PPII helix and favor the PPI helix, whereas capped termini favor the PPII over the PPI helix. These experimental findings are supported by the energy differences between the PPII and PPI helices of oligoprolines 1-4 computed by ab initio methods including electron-correlation effects (second-order Møller-Plesset perturbation theory, MP2). Furthermore, these quantum-chemical calculations show that differences in charge-dipole interactions are responsible for the experimentally and computationally observed relative stabilities. Although these electrostatic interactions between the terminal charges and the amide dipoles stabilize both helices, they are significantly stronger in the PPI helix where the amide bonds are oriented almost linear to the helix axis as compared to the PPII helix in which the amides are nearly perpendicular to the axis. Moreover, we demonstrate that a negative charge at the C-terminus has a more pronounced effect on the relative stability as compared to a positive charge at the N-terminus due to destabilization of the PPII helix by repulsive interaction between the C-terminal carboxylate with the neighboring amide bond. Studies at different pH values verified the electrostatic nature of the observed effects and demonstrate how changes in the protonation state can be used to deliberately stabilize the PPII helix over the PPI helix or vice versa.

Instability of Cationic Gold Nanoparticle Bioconjugates: The Role of Citrate Ions

Gold nanoparticles of 6, 8, and 16 nm, synthesized with HAuCl(4) and sodium citrate, were derived with biomolecules based on the peptide CIPGNVG and possessing different terminal charges. We have studied the stability of these conjugates as a function of ionic strength, pH, and the presence of other species in solution. It was observed that multiple electrostatic interactions between the conjugates mediated by cross-linking species led to an effective strong bond and consequently to irreversible aggregation and precipitation. In the presence of citrate or diamine ions, nanoparticles precipitated when two-headed ions had charges opposite (and therefore attractive) to the conjugate, thus acting as bridging molecules. This effect depends on the pH, the concentration of particles, and their size, and it is relevant to designing bioconjugates for biomedical applications.

Does trigger point mechanism create monopoly power for Hong Kong container terminals?

In recent years, the Hong Kong port has been challenged by the emergence of the Shenzhen port. This gives rise to a concern that the high terminal handling charges (THC) levied by the Hong Kong terminal operators are undermining the competitiveness of the Hong Kong port. As the major container terminals in both Hong Kong and Shenzhen are operated by the Hong Kong terminal operators, the monopoly power of these operators is commonly believed to be the cause of the high THC in Hong Kong. The theoretical model developed in this study shows that the trigger point mechanism (TPM) used by the Hong Kong Government to control the supply of terminal capacity may be a source of such monopoly power. Two possible scenarios are considered in the model—Scenario 1 in which expansion of capacity is unconstrained (i.e. the Shenzhen port); and Scenario 2 in which expansion of capacity is constrained by TPM (i.e. the Hong Kong port). Under TPM, the Hong Kong Government commits not to grant the right to build new container terminals unless and until the demand for container handling services exceeds the current capacity by a certain amount, which provides the incumbent operators incentives to invest preemptively in excess capacity in order to block the entry of potential entrants. This model is supported by the empirical findings from this study. The results from this study suggest an urgent need for the Hong Kong Government to overhaul the current port development policy as a part of the effort to promote economic integration between Hong Kong and the Mainland China.

A Compact Model of Silicon-Based Nanowire MOSFETs for Circuit Simulation and Design

A silicon-based nanowire FET (SNWT) compact model is developed for circuit simulation. Starting from the solution of poisson's equation, an accurate inversion charge expression is derived for SNWTs with arbitrary body doping concentration. The drain current, transconductance, output conductance, terminal charges, and capacitances are then calculated based on fundamental device physics. Short-channel and quantum effects have been included in the model in a self-consistent way. Comparison between the numerical simulation and analytical calculation shows that the proposed model is valid for all operation regions of SNWTs with different dimensions and channel doping. The model has been implemented in circuit simulators by Verilog-A, and its application in circuit simulation is also demonstrated.

Compact modeling of amorphous‐silicon thin‐film transistors with BSIM3

Abstract— A novel approach of modeling a‐Si:H TFTs with the industry‐standard BSIM3 compact model is presented. The described approach defines the a‐Si:H TFT drain current and terminal charges as explicit functions of terminal voltages using a minimum set of BSIM3 parameters. The set of BSIM3 parameters is chosen based on the electrical and physical characteristics of the a‐Si:H TFT and their values extracted from measured data. By using the selected BSIM3 model parameters, the a‐Si:H TFT is simulated inside SPICE to fit the simulated I‐V and C‐V curves with the measured results. Finally, the extracted BSIM3 model is validated by simulating the kickback voltage effect in an AMLCD pixel array.

Identification and characterization of a novel fibril forming peptide in fungal starch binding domain

Scanty information is available regarding the chemical basis for structural alterations of the carbohydrate-binding modules (CBMs). The N-terminal starch binding domain (SBD) of Rhizopus oryzae glucoamylase (GA) forms fibrils under thermal stress, presenting an unusual conformational change from immunoglobulin-like to β-sheet-rich structure. Site-directed mutagenesis revealed that the C-terminal Lys of SBD played a crucial role in the fibril formation. The synthetic peptide (DNNNSANYQVSTSK) representing the C-terminal 14 amino acid residues of SBD was further demonstrated to act as a fibril-forming segment, in which terminal charges and an internal NNNxxNYQ motif were key fibril-forming determinants. The formation of fibril structure in a fungal SBD, caused by its chemical and biophysical requirements, was demonstrated for the first time.

Carrier-based compact modeling of charge and capacitance of long channel undoped symmetric double-gate MOSFETs

Carrier-based compact modeling of terminal charges and intrinsic trans-capacitances of a long channel undoped symmetric double-gate MOSFET is presented in this paper. The explicit expressions for the terminal charges are obtained from a simplified carrier-based drain current model and the current continuity principle. Then analytic trans-capacitances are derived in terms of the charges at the source and drain ends. The validity of the analytic terminal charges and trans-capacitances is also verified by 2D numerical analysis proving the accuracy of the compact model presented here.

Analytic Carrier-Based Charge and Capacitance Model for Long-Channel Undoped Surrounding-Gate MOSFETs

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> Three terminal charges and nine intrinsic capacitances associated to the gate, source, and drain terminals of long-channel undoped surrounding-gate (SRG) MOSFETs are derived physically from an exact analytical solution of the channel current-continuity principle and channel charge-partition scheme in this paper. Although requiring lengthy and complex mathematical expressions, all explicit solutions for the capacitances can be obtained analytically. The validity of the analytical solutions is confirmed by comparing model predictions with simulation data obtained using the 3-D numerical solvers. The explicit expressions to the terminal charges and transcapacitance not only lead to a clearer understanding of SRG MOSFET device physics but also provide a better infrastructure to develop a complete carrier-based model for the SRG-MOSFET-based circuit simulation. </para>

Surface Potential-Based Polycrystalline Silicon Thin-Film Transistor Model

A surface potential-based polycrystalline silicon thin-film transistor (poly-Si TFT) model is proposed. Surface and grain boundary (GB) potentials are calculated by solving one-dimensional Poisson equations in both perpendicular and lateral directions to a poly-Si surface. A drain current model considers composite mobility to describe conductivities at both GB and intragrain, GB-induced mobility modulation, hot carrier effect, gate-induced drain leakage, and trap-dependent generation current. A capacitance model is derived from physically partitioned terminal charges and coupled to a drain current behavior. Furthermore, the poly-Si TFT model incorporates external resistances to express lightly doped drain structure and internal resistances to express non-quasi-static effects. Solving the Poisson equations not only allows for the accurate simulations of drain current and capacitance, but also well reproduces the dependence of TFT characteristics on grain size, GB trap density, and temperature. This poly-Si TFT model is successfully implemented into a circuit simulator and verified by ring-oscillator simulation. The good agreements with the measurements of both static and dynamic characteristics confirm the validity of the model.

PH-Activated Fusogenic Transmembrane LV-Peptides

LV-peptides mimic the in vitro fusogenicity of synthetic fusion protein transmembrane domains. The original versions of these peptides consist of a variable hydrophobic core (containing leucine and/or valine residues (LV)) that is flanked by invariant lysine triplets at both termini. Previously, peptide fusogenicity was correlated with the structural plasticity of their hydrophobic cores. Here, we examined the functional importance of positively charged flanking residues. To this end, we determined the fusogenicities of peptide variants that contain terminal His and/or Lys triplets. Interestingly, liposome fusion by peptides with His triplets was triggered by acidic pH. The pH dependence of fusion is reflected by a sigmoidal titration curve whose midpoint is close to the pKa value of histidine. Thus, only peptides with positively charged residues at both termini are fusogenic. The previously established dependence of fusogenicity on the sequence of the hydrophobic peptide core of Lys-flanked LV-peptides was preserved with the His-flanked versions at low pH. We propose that the structural flexibility of the core region as well as positive terminal charges are required for LV-peptide function in lipid mixing. In a potential practical application, the pH-dependent LV-peptides might prove to be useful in the lipofection of eukaryotic cells.

Multicommodity network flow model for Asia's container ports

This paper seeks to develop a multi-commodity network model to analyse the flow of containers within the Asia Pacific context. The model is used to evaluate the impact of container throughput in Asia's port by varying terminal handling charges and turnaround time. The three main regions analysed are north-east Asia, east Asia (Chinese port region) and south east Asia. Using the model, it could be shown that Busan port, which is an important transhipment hub in north-east Asia, could boost the container activities in the north-eastern part of China by improving its service quality. It is also found that the efficiency of the land link between Hong Kong and mainland China plays a crucial role for the future of Hong Kong port. While Singapore port maintains its position as a transhipment hub in south-east Asia, there would be expected competition from neighbouring low costs ports.

An analytic potential model for symmetric and asymmetric DG MOSFETs

This paper presents an analytic potential model for long-channel symmetric and asymmetric double-gate (DG) MOSFETs. The model is derived rigorously from the exact solution to Poisson's and current continuity equation without the charge-sheet approximation. By preserving the proper physics, volume inversion in the subthreshold region is well accounted for in the model. The resulting analytic expressions of the drain-current, terminal charges, and capacitances for long-channel DG MOSFETs are continuous in all operation regions, i.e., linear, saturation, and subthreshold, making it suitable for compact modeling. As no fitting parameters are invoked throughout the derivation, the model is physical and predictive. All parameter formulas are validated by two-dimensional numerical simulations with excellent agreement. The model has been implemented in Simulation Program with Integrated Circuit Emphasis version 3 (SPICE3), and the feasibility is demonstrated by the transient analysis of sample CMOS circuits.

Measurement of Thermodynamic Parameters for Hydrophobic Mismatch 2: Intermembrane Transfer of a Transmembrane Helix

Hydrophobic matching between proteins and lipids is essential for the thermodynamic stability of integral membrane proteins. However, there is no direct thermodynamic information available about the intermembrane transfer of proteins between membranes with different hydrophobic thicknesses, which is crucial for understanding hydrophobic mismatch. This article reports the complete set of thermodynamic parameters (DeltaG, DeltaH, DeltaS, and DeltaC(p)) for the intermembrane transfer of the inert hydrophobic model transmembrane helix NBD-(AALALAA)(3)-NH(2) (NBD: 7-nitro-2-1,3-benzoxadiazol-4-yl), which is exchangeable between vesicles, from 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) to dimonounsaturated-phosphocholine lipid bilayers with different hydrophobic thicknesses (C14-C22) at 37-58 degrees C. The transfer free energies were calculated from equilibrium values of the extent of helix transfer from donor to acceptor lipid vesicles, as monitored by a decrease in fluorescence resonance energy transfer from the NBD group to a lipid-labeled Rhodamine in the donor upon transfer to the quencher-free acceptor. Under hydrophobic mismatch conditions up to approximately 7 A, the helix partitioning became unfavorable up to +7 kJ mol(-)(1), hampered by an increase in entropic (up to +20 kJ mol(-)(1)) and enthalpic (up to +66 kJ mol(-)(1)) terms in thinner and thicker membranes, respectively. Together with the results that H/D exchange at the membrane interface was accelerated in thinner membranes the obtained thermodynamic parameters were reasonably explained assuming that hydrophobic mismatch induces aqueous exposure or membrane burial of the helix termini, resulting in excess energies originating from the hydration of terminal hydrophobic residues or the unfavorable Born energy of terminal partial charges of the helix macrodipole.

Structural Characterization of α-Helices of Implicitly Solvated Poly-Alanine

The structural characteristics of alpha-helices in poly-alanine-based peptides have been investigated via molecular dynamics simulation with the goal of understanding the basic features of peptide simulations within the context of a model system, classical molecular dynamics with generalized Born (GB) solvation, and to shed insight into the formation and stabilization of alpha-helices in short peptides. The effects of peptide length, terminal charges, proline substitution, and temperature on the alpha-helical secondary structure have been studied. The simulations have shown that distinct secondary structure begins to develop in peptides with lengths approaching 10 residues while ambiguous structures occur in shorter peptides. The helical content of peptides with lengths > or =10 amino acids is observed to be nearly constant up to (Ala)(40). Interestingly, terminal charges and proline in the second position from the N-terminus alter the secondary structure locally with little effect on the overall alpha-helical content of the peptide. The free energy profile of helix formation was also investigated. A large increase in free energy accompanying the formation of helices with more than two consecutive hydrogen bonds in the (i, i + 4) pattern was observed while the free energy increases linearly with additional hydrogen bonds. Values for the change in enthalpy and entropy of helix nucleation and propagation are reported. Additionally the results obtained from the GB model are compared to explicit solvent simulations of two synthetic alanine-based peptides.

New fundamental insights into capacitance modeling of laterally nonuniform MOS devices

In compact transistor modeling for circuit simulation, the capacitances of conventional MOS devices are commonly determined as the derivatives of terminal charges, which in their turn are obtained from the so-called Ward-Dutton charge partitioning scheme. For devices with a laterally nonuniform channel doping profile, however, it is shown in this paper that no terminal charges exist from which the capacitances can be derived. Instead, for such devices, a new model is presented for the capacitances themselves. Furthermore, a method is given to incorporate such a capacitance model into circuit simulators, which are traditionally based on terminal charge models. Comparison with two-dimensional device simulations and a segmentation model shows that for a constant mobility, the new capacitance model provides an accurate description for a MOSFET with a laterally diffused channel doping profile. Through a comparison with high-frequency measurements, the agreement between model and experimental results is discussed.

Effects of the terminal charges in human neutrophil α-defensin 2 on its bactericidal and membrane activity

Human neutrophil α-defensin 2 (HNP2) was N-terminally acetylated and/or C-terminally amidated, resulting in three terminally modified analogs, Ac-HNP2, HNP2-NH 2 and Ac-HNP2-NH 2. We examined their bactericidal activity against E. coli and S. aureus and their ability to induce leakage from large unilamellar vesicles. Loss of the N-terminal positive charge was functionally deleterious, whereas removal of the C-terminal negative charge enhanced microbial killing and membrane permeabilization. Our findings validate the importance of electrostatic forces in defensin–microbe interactions and point to the bacterial cytoplasmic membrane as a target of HNP2 activity.

Physics-Based Single-Piece Charge Model for Strained-Si MOSFETs

A physics-based single-piece charge model for strained-silicon (s-Si) MOSFETs from accumulation to strong-inversion regions is presented. The model is formulated from regional solutions of the well-known Pao-Sah equation and unified with interpolation functions while keeping the physics in the derived flat-band voltages that depend on the device material and structural parameters, such as band gaps, conduction and valence band offsets, Ge mole fraction, layer thickness, and doping. The model is validated by comparison with numerical devices for a wide range of Ge mole fractions and s-Si layer thicknesses. It is shown that the model accurately describes the physical behavior of the surface potentials, terminal charges and capacitances, especially charge accumulation/depletion at the s-Si/SiGe interface that gives rise to the observed "plateau" in the capacitance-voltage characteristics.