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In this article, we present a surface-potential-based approach to model the bias-dependent effective velocity observed in AlGaN/GaN high-electron-mobility transistors (HEMTs) due to optical phonon scattering. Our model precisely reproduces the progressive decrease in the saturation velocity in GaN HEMTs with increasing gate voltages, as reported in the literature, which is predominantly due to the scattering of electrons, forming the high-density two-dimensional electron gas (2DEG), by optical phonons at high overdrive voltages. We show that this dependence differs from the traditional mobility degradation models in terms of its impact on the device current–voltage ( ${I}$ – ${V}$ ) characteristics and illustrate how the inclusion of a velocity saturation model also provides the model users with an additional handle for parameter extraction. The model is explicit and, by virtue of its Simulation Program with Integrated Circuit Emphasis (SPICE) compatibility, is readily implemented in the industry-standard Advanced SPICE Model for HEMTs (ASM-HEMTs) model and has been validated against experimental dc ${I}$ – ${V}$ and RF S-parameter measurements of an in-house GaN device.

Background: Diabetes is a chronic metabolic disease because of the elevated levels of glucose in the blood. And usually most of the diabetic patients are left undiagnosed in their early stages of the disease because of the unnoticeable symptomsby the patients which could lead to the severe damage to the body system, hence an early diagnosis is very important and life saving indiabetic patients. Aim: aim of the present study is to evaluate the accuracy of gingival crevicular blood as a diagnostic tool in diabeticpatients. Methods: This study involves total 50 patients 25 diabetic and 25 non diabetic patients, with moderate to severe periodontitis. Regular dental check-up is done including periodontal pocket depth probing. Blood oozing from the gingival crevice was collected with the strips of glucose self monitoring devise. To the same patient finger stick Blood glucose level and venous blood[ VB] glucose level with standardized laboratory method was taken. Results: The results showed significant strong correlation between all three groups. With p value (P < 0.001). Conclusion: Blood oozing during the pocket detection can be used for diagnosing aid in diabetes. Keywords: gingival crevicular blood, Finger stick blood, venous blood, diabetes mellitus, Glucometer, chronicperiodontitis.

In this article, we report the development of a novel physics-based analytical model for explaining the current–voltage relationship in Schottky barrier (SB) 2-D-material field effect transistors (FETs). The model has at its core the calculation of the surface-potential (SP) which is accomplished by invoking 2-D density of states in conjunction with Fermi–Dirac (FD) distribution for electron and hole statistics. The explicit computation for the SP, carried out using the Lambert-W function together with Halley’s method, is used to construct the SP-based band-diagram for realizing the transparency of the SBs. Thereafter, the ambipolar current is derived in terms of the electron and hole injection phenomena—the thermionic emission and Fowler–Nordheim tunneling mechanisms—at the SB contacts. Furthermore, drift-diffusion current is derived in terms of the SP and incorporated in the model to account for the scattering in the intrinsic 2-D channel. Finally, the Verilog-A model is validated against experimental ${I}-{V}$ data reported in the literature for two different 2-D-material systems. This is the first demonstration of an explicit SP-based SPICE model for ambipolar SB-2-D-FETs that is simultaneously built on tunneling-emission and drift-diffusion formalisms.

In this work, we present a tenably accurate and computationally efficient analytical calculation of the surface potential in organic thin-film transistors (OTFTs). Double exponential density of states is used to model deep and tail trap states for carrier electrostatics. We employ the Lambert-W function to obtain the analytical surface potential expression. The validity of the obtained expressions is ascertained through a comparison between the numerical and explicit expressions. Furthermore, we also build on a model that was based on Lagrange Reversion theorem and test its validity for different biasing conditions. The proposed model, by virtue of its explicit analytical nature, while preserving the underlying physics, is suitable for the development of surface-potential-based compact models for OTFTs, which can be used for circuit design.

We report a charge-based analytic and explicit compact model for field effect transistors (FETs) based on two-dimensional materials (2DMs), for the simulation of 2DM- based analog and digital circuits. The device electrostatics is handled by invoking 2D density of states and Fermi-Dirac statistics, that are later combined with Lambert-W function and Halley’s correction, so to eventually obtain explicit expressions for the electron and hole charges, which are exploited in the calculation of drift-diffusion currents for both carriers. Further, the charge model is extended to obtain characteristics of 2DM- based negative capacitance FETs. The model is benchmarked against experimental MoS2 FET measurements, and experi- mental ambipolar characteristics of narrow band-gap materials such as black phophorous. Its soundness for SPICE circuit-level simulations is also demonstrated.

We present the latest developments in Advance SPICE Model for GaN (ASM GaN) HEMTs in this paper. The ASM GaN model has been recently selected as an industry-standard compact model for GaN radio frequency (RF) and power devices. The core surface-potential calculation and the modeling of real device effects in this model are presented. We discuss the details of the nonlinear access region model and enhancement in this model to include a physical dependence on barrier thickness. We also present the novel model feature of configurable field-plate modeling and discuss the extraction procedure for the same. New results with the ASM GaN model on high-frequency and enhancement-mode GaN power devices are also presented.

In this paper, a consistent DC to RF modeling solution for Al gallium nitride (GaN)/GaN high electron mobility transistors is demonstrated that is constructed around a surface-potential-based core. Expressions for drain current and intrinsic terminal charges in the form of surface-potential are used to simultaneously model the DC characteristics and the intrinsic capacitances of a commercial GaN device. Self-heating and trapping effects are incorporated to account for the non-linear nature of the device. We discuss the parameter extraction flow for some of the key model parameters that are instrumental in fitting the DC characteristics, which simultaneously determines the bias-dependent intrinsic capacitances and conductances that significantly eases the RF parameter extraction. Parasitic capacitances, gate finger resistance, and extrinsic bus-inductances are extracted, from a single set of measured non-cold-FET S-parameters, using the model process design kit. The extraction procedure is validated through overlays of broadband (0.5-50 GHz) S-parameters, load-pull and harmonic-balance (10 GHz) simulations against measured data, under multiple bias conditions to successfully demonstrate the model performance at large-signal RF excitations.

In this paper, we present a capacitance model for field-plate AlGaN/GaN High Electron Mobility Transistor (HEMTs) accounting for the contribution of substrate capacitances and cross-coupling between field plates. TCAD simulations are performed to analyze both these contributions and analytical expressions for charges corresponding to the cross-coupling and substrate capacitances are presented in terms of our existing surface-potential-based model. The modeled results are validated by comparing the time-domain waveforms of a test circuit using a mixed-mode simulation setup in which the impact of cross-coupling and substrate capacitances on accuracy of switching transients predicted by the model is discussed.

In this letter, we propose a method to extract the small-signal equivalent circuit model for GaN HEMTs using extrinsic-level RF broadband (0.5–50 GHz) Z-parameters. The measured Z-parameters of large gate-periphery GaN devices exhibit certain interesting characteristics, due to their inherently larger intrinsic capacitances and their subsequent interaction with the extrinsic inductances. We exploit these characteristics to simultaneously extract the intrinsic as well as the extrinsic small-signal model components and successfully validate it with measured S-parameter data for a $10~\times90~\mu \text{m}$ GaN device.

In this letter, we present a novel approach toward understanding the Kink effect (KE) in the bode plot of short circuit current gain ( ${h_{21}}$ ) observed for microwave transistors, particularly gallium nitride (GaN) HEMTs. We ascribe the origin of the KE to the presence of a pair of complex conjugate poles at the frequency of interest, introduced due to the extrinsic parasitic inductances and their interaction with the device intrinsic elements, such as the capacitances and transconductance, and develop simplified mathematical expressions that govern the behavior of the kink. We also present a physics-based compact model that is capable of capturing the KE and extensively validate the model against measured data for a GaN device under multibias conditions, thereby advocating the strong physical background of the model. We conclude by demonstrating the impact of various elements of the small signal model on the kink based on the developed mathematical hypothesis for KE.

In this paper, the impact of source via-inductance on stability performance of large gate-periphery RF transistors is investigated in terms of Rollett’s stability factor (K-factor) using a small-signal equivalent circuit model. The RF device-under-test studied in this work is a commercial multi-finger GaN HEMT with a considerably large gate-periphery of 10 × 90 µm. A systematic analysis of the K-factor is done by deriving its mathematical expression in terms of the equivalent circuit intrinsic and extrinsic components. While gate-to-drain capacitance is unanimously considered to be the most critical component in determining the device stability performance, due to the formation of the feedback loop, the simulation and experimental results obtained in this work reveal potential regions of device instability in the form of peaks and valleys, that emerge as a manifestation of the coupling between the via-inductance and the intrinsic drain-to-source capacitance. This study is of significance particularly to multi-finger large gate-periphery devices since they have a reduced gate-resistance and therefore are driven further into instability. This work is expected to serve as a guideline in obtaining optimized multi-finger RF transistors with regard to stability.

In this paper, we present a physics based compact model for GaN-based Metal-Semiconductor-Metal (MSM) 2DEG varactors in which the intrinsic charges and currents are evaluated in terms of the bias-dependent surface-potential. Physical phenomena such as Thermionic Emission, Poole-Frenkel Effect and Fowler-Nordheim Tunneling are incorporated to realize the non-idealities of the Schottky gates. The model is successfully validated against measured data for a state-of-the-art GaN-based varactor. Furthermore, a circuit simulation is performed for a phase shifting network wherein its behavior for various bias conditions and operating frequencies is observed using the proposed model.

In this paper, a surface-potential-based compact model is proposed for the capacitance of an AlGaN/GaN high-electron mobility transistor (HEMT) dual field-plate (FP) structure, i.e., with gate and source FPs. FP incorporation in a HEMT gives an improvement in terms of enhanced breakdown voltage, reduced gate leakage, and so on, but it affects the capacitive nature of the device, particularly by bringing into existence in a subthreshold region of operation, a feedback miller capacitance between the gate and the drain, and also a capacitance between the drain and the source, therefore, affecting switching characteristics. Here, we model the bias dependence of the terminal capacitances, wherein the expressions developed for intrinsic charges required for capacitance derivation are analytical and physics-based in nature and valid for all regions of device operation. The proposed model, implemented in Verilog-A, is in excellent agreement with the measured data for different temperatures.

In this paper we present the dependence of Gallium nitride (GaN) high electron mobility transistor (HEMT) AM/AM and AM/PM non-linearities on AlGaN barrier layer thickness (Tbar). While the effect of barrier layer thickness on two-dimensional electron gas density has been shown earlier, in this paper we show for the first time that Tbar affects the non-linear behavior of the device through the changes in channel effective mobility and capacitances. We accurately model five different GaN HEMT devices with Tbar varying from 8 nm to 25 nm using a physics-based model and use the developed accurate model as a tool to analyze the non-linear behavior of the GaN HEMT device.

In this paper, we aim to present a surface potential based model for GaN High Electron Mobility Transistors. The analytical model is computationally efficient and can be accurately used for DC and RF predictions. It includes various effects of velocity saturation, access region resistance, temperature, gate current and noise.

In this paper, we aim to present an overview of a surface-potential (SP) based model named “Advanced Spice Model for High Electron Mobility Transistor” (ASM-HEMT) for AlGaN/GaN HEMTs. This model is presently under consideration in the phase-III of industry standardization by the Compact Model Coalition (CMC). SP of GaN HEMT is obtained by solving Schrodinger and Poisson equations in the triangular potential well considering the first two energy subbands. The core drain current model and a intrinsic charge model are derived using the developed SP model. Various real device effects like: velocity saturation, drain-induced barrier lowering (DIBL), self-heating, field dependent mobility, non-linear access region resistances etc. are included in the core drain current model to represent real GaN HEMTs. Field-plate (FP) model is incorporated to predict accurate current and capacitance trends observed in the high power GaN HEMTs with source and gate connected field-plates. Along with the gate current model, non-linear trapping effects are also included in the model to capture larghe-signal high-frequency device behavior. This model is extensively validated with the experimental data of both high power and high frequency GaN HEMTs.

The aim of this study to analyze whether ultrastaging of initially negative nonsentinel lymph nodes (non-SLNs) would increase nodal positivity in colon cancer and rectal cancer.After SLN mapping (SLNM), SLNs were ultrastaged by 4 hematoxylin and eosin and 1 immunohistochemistry sections. A blinded pathologist reexamined initially negative non-SLNs by 3 additional hematoxylin and eosin and 1 immunohistochemistry sections.In 156 colon cancer and 44 rectal cancer patients, 2,755 nodes were identified (494 SLNs and 2,261 non-SLNs). Metastases were detected in 20.9% of SLNs and 8.6% of non-SLNs (P.0001). After ultrastaging non-SLNs, only .58% became positive for metastases in 12 patients. Of these, 10 already had positive lymph nodes, hence no change of staging occurred. Ultrastaging upstaged only 2 of 200 patients (1%).The chance of finding additional metastases by ultrastaging of all non-SLNs is extremely low (1%) and of little benefit.

In this work, we study the trapping in GaN power HEMTs and discuss effect of traps on device characteristics. Simulation setups for analysis of switching collapse and current collapse observed in pulsed I–V are also presented. We propose an RC network based trap model to capture the effect of trapping in a surface potential based compact model for GaN HEMTs. The proposed model has been verified with the hardware data for various quiescent biases and frequencies, and the model results are in excellent agreement with the hardware data.

Incorporation of Field Plate in High Electron Mobility Transistors (HEMTs) improves the device breakdown voltage but on the other hand, increases the device Capacitance. It has a direct impact on the device switching characteristics and hence the study of the capacitive behavior holds supreme importance for GaN HEMTs power switching application. Also, in GaN HEMTs, lower values of access region resistance improves the device output current but at the cost of increase in its capacitance, C GD . In this paper, using TCAD simulations on a field plated GaN HEMT, we present the physical explanation for the variation in C-V characteristics for different access region and field plate lengths.

Background Fascin is an actin cross-linking protein, which is part of the cytoskeleton and involved in cell motility in several cell types. The differentiation of epithelial cells is greatly influenced by cell–matrix and cell–cell interactions, which play an important role in the normal organisation and stabilisation of epithelial cells and maintain the cells in a non-migratory state. The malignant conversion of epithelial cells results from a phenotypic switch to a migratory state, which allows tumour invasion beyond the basement membrane, as well as metastasis. Such a switch requires complex rearrangements of the actin cytoskeleton and is governed by multiple actin-binding proteins including fascin. In non-neoplastic lymphoid tissue, fascin expression is highly selective and is predominantly localised in dendritic cells, while lymphocytes, plasma cells, etc are uniformly non-reactive. However, all or nearly all Reed–Sternberg cells and their variants in all types of Hodgkin9s lymphoma express fascin and are strongly immunoreactive for fascin. Conclusion Lymphomas (Hodgkin9s and non-Hodgkin9s) are among the commonest malignancies seen in our practice. The Section of Histopathology at the Aga Khan University, Karachi is the largest centre for histopathology in Pakistan, a densely populated country with an estimated population of 170 million. The authors wanted to test the utility of Fascin in distinguishing between Hodgkin9s lymphoma and morphologically closely related forms of non-Hodgkin9s lymphoma such as diffuse large B cell non-Hodgkin9s lymphoma and anaplastic large cell lymphoma in difficult cases. If found useful, this antibody could help us in reaching a correct diagnosis in difficult cases and allow appropriate patient management.

A 27 year old female presented with two months history of continuous vaginal bleeding. On evaluation, she was diagnosed as a case of vaginal clear cell adenocarcinoma (VCCA) along with associated Müllerian duct anomalies including didelphys uterus with double vagina; left sided renal agenesis and situs inversus. Although VCCA is strongly linked to in-utero exposure with Diethyl stillboestrol (DES), this patient had no known history regarding such exposure. Also, only a few cases have been described in the literature in which this tumour was seen in association with Müllerian duct anomalies and renal agenesis; in the absence of known DES exposure.

Primary Cutaneous lymphomas of B cell origin are rare, there remains a controversy in truly classifying these lymphomas and an updated EORTC classification divides them on the basis of their distinct histopthological grounds rather than on the basis of their anatomic location as in WHO classification, while the new WHO- EORTC joint classification maintains some characteristics of both systems, We report an elderly gentleman who primarily had a typical Leg dominant Cutaneous lymphoma of B cell origin uniquely with involvement of nasal Sinusues, bearing the Immunohistochemical staining features of "Cutaneous lymphoma - Leg Type" befitting the new joint WHO-EORTC classification of Cutaneous B cell Lymphoma.

We discuss a case of 25 year old male who was evaluated for primary infertility following marriage. He had no previous history of urogenital complaints or abnormalities. In fact, his past medical history was unremarkable. On examination epididymal masses were found. Semen analysis showed azoospermia. Right epididymal mass was surgically excised. Histopathology showed an epididymal neoplasm composed of simple and complex papillary processes lining and filling the ducts. The tumor cells were clear and positive for cytoplasmic glycogen. Immunohistochemistry was also supportive. Diagnosis of clear cell papillary cystedenoma was made based on histopathological and immunohistochemical features.

To determine in a large series of surgical biopsies, the frequency of various histologic types of primary solid malignant neoplasms in males and females in different age groups.A retrospective study of 20,000 consecutive surgical biopsies reposted in the section of histopathology, AKU in 2004.Malignant neoplasms are commonest in the fifth and sixth decades of life. The commonest malignant neoplasms in the first decade were Hodgkin's lymphoma and Wilm's tumor in males and females respectively. In the second decade, osteosarcoma in males and Ewing's sarcoma / PNET in females. In the third decade, colorectal adenocarcinoma in males and infiltrating. Ductal carcinoma of breast in females. In the fourth decade, squamous cell carcinoma of oral cavity in males and infiltrating ductal carcinoma of breast in females. In the fifth decade squamous cell carcinoma of oral cavity in males and infiltrating ductal carcinoma of breast in females. In sixth decade, squamous cell carcinoma of oral cavity in males and infiltrating ductal carcinoma of breast in females and in the seventh decade, prostatic adenocarcinoma in males and infiltrating ductal carcinoma of the breast in females. Above age of 70 years, the commonest malignant were again prostatic adenocarcinoma in males and infiltrating ductal carcinoma of breast in females.Malignant neoplasms are commonest in the fourth, fifth and sixth decades of life.

To determine the frequency of various histologic types of primary solid malignant neoplasms in males and females, in our practice, in a large series of surgical biopsies.A retrospective study of 20,000 consecutive surgical biopsies in the section of Histopathology, Aga Khan University Hospital (AKU), Karachi, in 2004.Squamous cell carcinoma of oral cavity was the commonest malignant neoplasm in males followed by diffuse Large B cell, Non-Hodgkin's lymphoma and Prostatic adenocarcinoma. In females, infiltrating Ductal carcinoma of the breast was overwhelmingly the commonest malignant neoplasm followed by Squamous cell carcinoma of the oral cavity and esophagus.Out of 20,000 biopsies, there were 4616 (23.08%) malignant neoplsms. Carcinoma of oral cavity is very common in our population in both sexes.

Post-Transplant Lymphoproliferative Disorder (PTLD) is a lymphoma, which develops as a result of immunosuppression in a recipient of a solid organ or bone marrow allograft. Majority are associated with Ebstein-Barr Virus (EBV) infection, are mostly B-cell type and less often T-cell type. We report a case of T-cell PTLD, occurring in a renal transplant recipient.

To re-classify thymic epithelial neoplasms reported at Aga Khan University Hospital during the past seven years according to the revised WHO classification, to assess the ease of application and determine association between WHO histological subtype and invasive behaviour.Descriptive study.The study was carried out in the section of Histopathology, Department of Pathology and Microbiology, Aga Khan University Hospital, Karachi, from January 2000 to October 2006.All cases of thymic epithelial neoplasms reported in the past seven years were retrieved using SNOMED coding system. Small biopsies where the tissue was insufficient for definite classification were not included. All cases were reviewed and reclassified according to WHO classification into types A, AB, B1, B2 and B3. Capsular invasion as well as extension into neighboring structures such as perithymic fat, pleura, pericardium, lung etc. was noted on morphology.A total of 62 cases were diagnosed as Thymic Epithelial Tumors (TET). Out of these, there were 5 type A (6 %), 17 type AB (21%), 7 type B1 (8.6%), 26 type B2 (32%) and 7 type B3 (8.6%) thymomas. Age range was from 22-78 years with a median age of 46 years. Male to female ratio was 6:1. History of associated myasthenia gravis was present in 21% of cases. A significant association was observed between WHO histologic subtype and invasive behaviour where types A, AB and B1 have lesser number of invasive cases as compared to non-invasive, whereas in types B2 and B3, more cases have shown invasion as compared to non-invasive cases (c2 = 14.093, df =1, p-value0.001 ).The WHO classification is simple and easy to apply and has significant association with aggressive behavior. To some extent, it reflects the clinical behaviour of thymomas along with stage and status of resection. However, morphologically benign looking thymomas can behave aggressively. Hence, tumour stage, extent of resection and histology should be combined to predict the clinical behaviour of thymomas.

Subependymal giant cell astrocytomas (SEGAs) are slowly growing tumours corresponding to WHO grade I. They are intraventricular and usually occur in the setting of tuberous sclerosis complex. They often result in obstructive hydrocephalus. Treatment is usually restricted to surgical resection, recurrences are rare and long term prognosis is excellent. We present a series of three cases.

Angiokeratomas (AC) are vascular lesions which are defined histologically as one or more dilated blood vessels lying directly subepidermal and showing an epidermal proliferative reaction with ectatic capillaries in the papillary dermis. Only three other cases of isolated mucosal angiokeratoma have been reported in the indexed literature. We reviewed all cases of angiokeratoma located on the tongue, diagnosed in our department during a study period of 10 years (1995-2005). Histologically all 14 cases showed dilated and congested blood vessels in the upper papillary dermis. They lack deep dermal involvement. Hyperkeratosis and acanthosis were also seen in most of the cases. No clinical data was available to assess systemic disease. A higher incidence of of AC in tongue is seen in our study.

Background.—The identification of lymph node metastases in colorectal resection specimens is necessary for accurate tumor staging. However, routine lymph node dissection by the pathologist yields only a subset of nodes removed surgically and may not include those nodes most directly in the path of lymphatic drainage from the tumor. Intraoperative mapping of such sentinel lymph nodes (SLNs) has been reported in cases of melanoma and breast cancer. We applied a similar method to cases of colorectal carcinoma, with emphasis on the pathology of the SLNs. Methods.—Eighty-three consecutive patients with colorectal carcinoma were evaluated after intraoperative injection of 1 to 2 mL of 1% isosulfan blue dye (Lymphazurin) into the peritumoral subserosa. Blue-stained lymph nodes were suture-tagged by the surgeon within minutes of the injection for identification by the pathologist, and a standard resection was performed. Designated SLNs were sectioned at 10 levels through the block; a cytokeratin immunostain (AE1) was also obtained. To evaluate the possibility that increased detection of metastases in the SLN might be solely due to increased histologic sampling, all initially negative non-SLNs in the first 25 cases were sectioned also at 10 levels. Results.—Sentinel lymph nodes were identified intraoperatively in 82 (99%) of 83 patients and accounted for 152 (11.9%) of 1275 lymph nodes recovered, with an average of 1.9 SLNs per patient. A total of 99 positive lymph nodes (38 positive SLNs and 61 positive non-SLNs) were identified in 34 node-positive patients. The SLNs were the only site of metastasis in 17 patients (50%), while 14 patients (41%) had both positive SLNs and non-SLNs. Three patients (9%) had positive non-SLNs with negative SLNs, representing skip metastases. In patients with positive SLNs, 91 (19%) of 474 total lymph nodes and 53 (12%) of 436 non-SLNs were positive for metastasis. In patients with negative SLNs, 8 (1%) of 801 total lymph nodes and 8 (1.2%) of 687 non-SLNs were positive for metastasis. Multilevel sections of 330 initially negative non-SLNs in the first 25 patients yielded only 2 additional positive nodes (0.6%). All patients with positive SLNs were correctly staged by a combination of 4 representative levels through the SLN(s) together with a single cytokeratin immunostain. Conclusions.—Intraoperative mapping of SLNs in colorectal carcinoma identifies lymph nodes likely to contain metastases. Focused pathologic evaluation of the 1 to 4 SLNs so identified can improve the accuracy of pathologic staging.