Primary Calvarial Tuberculosis: a report of three cases.

Calvarial tuberculosis is rare presentation and has been reported in only about 0.01% of all patients with mycobacterial infections. Though rare, the incidence of Calvarial tuberculosis seems to be on the rise, especially in developing countries. We present three cases of Calvarial tuberculosis which were successfully managed at our Centre. All the cases occurred de novo in young, otherwise healthy individuals, hailing from good socio-economic backgrounds and without any past history or contact history with tuberculosis patients. We highlight the importance of keeping this diagnosis in mind in appropriate clinical situations as well as recommend the early commencement of optimal management to prevent serious neurologic complications & sequelae.

Design of fractional order PID controller for load frequency control system with communication delay.

This work explores a frequency-domain approach to design a fractional order proportional-integral-derivative (FO-PID) controller cascaded with a first-order filter for the load frequency control (LFC) system with communication delay. The proposed method is based on suitable reference model development in the direct synthesis (DS) approach, followed by frequency response matching technique. The reference model is developed for robust control-loop performance using the stability-margin and time-domain specifications. The values of the fractional orders of the integral and derivative terms are obtained according to the dynamics of the nominal system. The proposed controllers have been designed for some LFC systems taken from the literature that have different dynamics with reheat, non-reheat and hydraulic turbines and performances with non-linearity like generation rate constraint (GRC), generation dead band (GDB) along with noise have been compared favorably with that of some controllers prevalent in the literature. The proposed controllers have been shown to work efficaciously for the decentralized multi-area IEEE 39-bus New England test system along with variable communication delay. To show the efficacy of the proposed controllers the load-disturbance responses along with the frequency and time domain performance indices have been evaluated for comparison.

A Prospective Study Comparing the Three-Dimensional Rotational Angiography and Two-Dimensional Digital Subtraction Angiography in Evaluation of Brain Arteriovenous Malformations.

Background: Complex angioarchitecture of brain arteriovenous malformations (BAVM) are often difficult to evaluate with standard imaging technique of digital subtraction angiography (DSA). These details are better provided by 3D rotational angiography (3D-RA). Objective: The aim of the study is to compare two-dimensional digital subtraction angiography (2D-DSA) and 3D rotational angiography in the evaluation of BAVM angiographic architecture. Materials and Methods: 2D-DSA and 3D-RA of 167 consecutive patients with BAVM were analyzed for arterial feeders, nidal patterns, and detection of flow-related aneurysms, arteriovenous fistulous components, venous drainage, and draining vein stenosis. Results: 3D-RA detected a significantly higher number of aneurysms and draining venous stenoses (P < 0.001). The detected number of true intranidal aneurysms was significantly higher with 3D-RA (n = 94) vs 2D-DSA (n = 34) (P < 0.001). 2D-DSA has low sensitivity (43.1%) and specificity (73.4%) for detecting intranidal aneurysms. 3D-RA detected a significantly higher number (12.6%) of BAVM patients with feeding artery aneurysms as compared to 2D-DSA (8.4%), P value of 0.004. 3D-RA accurately depicted the distal course of dominant arterial feeders and fistulous sites in BAVMs. Direct arteriovenous communications were evident in 31.1% with 3D-RA, as compared to 2D-DSA (15%) with P value < 0.0001. A significantly higher number of draining vein stenosis was detected with 3D-RA (21.6%) as compared to 2D-DSA (13.2%), P value < 0.001. Conclusion: 3D-RA is better than 2D-DSA for detecting BAVM-associated flow-related aneurysms, distal course of the dominant arterial feeders, direct visualization of the fistulous components, deep venous drainage, and draining venous stenosis; findings imperative for making a prudent therapeutic decision.

Centralized PI controller design method for MIMO processes based on frequency response approximation.

A simple method of controller design for multi-input multi-output (MIMO) processes have been proposed in frequency domain. The intensive calculation for the inverse of the process transfer function matrix is simplified to a great extent by evaluating the process transfer function matrix at a low frequency point. The desired closed loop transfer functions are derived for the process using a single tuning parameter for each diagonal element of the process transfer function matrix which represents the desired closed loop time constant. Centralized PI controllers are then designed using a model matching technique by evaluating the transfer functions at a low frequency point. The PI controllers provide acceptable performances for lag dominated as well as time-delay dominated processes and is also applicable to high-dimensional processes. The proposed method is extended for the non-square MIMO processes using two approaches one of which squares up the process transfer function matrix to apply the proposed technique while the other is based on pseudo-inverse evaluation of the process transfer function matrix at a low frequency point.

A pictorial review of brain arterial spin labelling artefacts and their potential remedies in clinical studies.

Arterial spin labelling is an emerging non-invasive magnetic resonance imaging technique for estimating the cerebral perfusion without the requirement for gadolinium-based intravenous contrast agents. Despite the wide range of applications in epilepsy, dementia, brain tumours, vascular malformations and stroke imaging, obtaining clinically useful arterial spin labelling data is technically challenging and prone to numerous artefacts. The objective of this review is to provide a comprehensive pictorial overview of the various artefacts associated with arterial spin labelling, particularly three-dimensional fast spin echo pseudocontinuous arterial spin labelling with spiral readout. These artefacts could be broadly classified as those occurring during the magnetic labelling, arterial transit or image acquisition. Arterial spin labelling artefacts of clinical diagnostic utility are also elaborated. A thorough knowledge of the basis of these artefacts will avoid diagnostic pitfalls while interpreting arterial spin labelling images. Important tips to reduce or overcome these artefacts are also discussed.

Model based PI power system stabilizer design for damping low frequency oscillations in power systems.

This paper explores a two-level control strategy by blending local controller with centralized controller for the low frequency oscillations in a power system. The proposed control scheme provides stabilization of local modes using a local controller and minimizes the effect of inter-connection of sub-systems performance through a centralized control. For designing the local controllers in the form of proportional-integral power system stabilizer (PI-PSS), a simple and straight forward frequency domain direct synthesis method is considered that works on use of a suitable reference model which is based on the desired requirements. Several examples both on one machine infinite bus and multi-machine systems taken from the literature are illustrated to show the efficacy of the proposed PI-PSS. The effective damping of the systems is found to be increased remarkably which is reflected in the time-responses; even unstable operation has been stabilized with improved damping after applying the proposed controller. The proposed controllers give remarkable improvement in damping the oscillations in all the illustrations considered here and as for example, the value of damping factor has been increased from 0.0217 to 0.666 in Example 1. The simulation results obtained by the proposed control strategy are favourably compared with some controllers prevalent in the literature.

A frequency response model matching method for PID controller design for processes with dead-time.

In this paper, a PID controller design method for the integrating processes based on frequency response matching is presented. Two approaches are proposed for the controller design. In the first approach, a double feedback loop configuration is considered where the inner loop is designed with a stabilizing gain. In the outer loop, the parameters of the PID controller are obtained by frequency response matching between the closed-loop system with the PID controller and a reference model with desired specifications. In the second approach, the design is directly carried out considering a desired load-disturbance rejection model of the system. In both the approaches, two low frequency points are considered for matching the frequency response, which yield linear algebraic equations, solution of which gives the controller parameters. Several examples are taken from the literature to demonstrate the effectiveness and to compare with some well known design methods.