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Biomedical subjects

K K Tan

Publications and source records attributed to K K Tan.

At least 19 recordsLinked to original sources
PubMed2003

Feedforward suppression of force ripple based on a simplex-optimized dither signal.

This paper presents the design and realization of a feedforward dither signal to reduce the force ripple in an iron-core permanent magnet linear motor (PMLM). A composite control structure is used, consisting of three components: a simple feedforward component, a PID feedback component, and a ripple compensator (RC). The first two components are designed based on a dominant linear model of the motor. The dither signal is generated based on a signal model which is identified using a multidimensional simplex downhill method. In this way, a simple approach is available to eliminate or suppress the inherent force ripple, thus facilitating smooth precise motion while uncompromising on the maximum force achievable. Real-time experimental results verify the effectiveness of the proposed scheme for high precision motion trajectory tracking.

Algorithms↗
PubMed2003

Relay-enhanced multi-loop PI controllers.

In this paper, the development of relay-enhanced multi-loop PI controllers is described for multivariable processes. The control system employs a relay in series with the controller. The relay can ensure a satisfactory level of closed-loop performance and it also yields oscillations for tuning of the PI controller based on an equivalent process model for each loop. A simulation example [on a two-inputs-two-outputs (TITO) process] is provided to illustrate the effectiveness of the proposed method and to compare its performance to an existing method.

Journal Article↗
PubMed2003

Multistability analysis for recurrent neural networks with unsaturating piecewise linear transfer functions.

Multistability is a property necessary in neural networks in order to enable certain applications (e.g., decision making), where monostable networks can be computationally restrictive. This article focuses on the analysis of multistability for a class of recurrent neural networks with unsaturating piecewise linear transfer functions. It deals fully with the three basic properties of a multistable network: boundedness, global attractivity, and complete convergence. This article makes the following contributions: conditions based on local inhibition are derived that guarantee boundedness of some multistable networks, conditions are established for global attractivity, bounds on global attractive sets are obtained, complete convergence conditions for the network are developed using novel energy-like functions, and simulation examples are employed to illustrate the theory thus developed.

Linear Models↗
PubMed2002

Dynamic stability conditions for Lotka-Volterra recurrent neural networks with delays.

The Lotka-Volterra model of neural networks, derived from the membrane dynamics of competing neurons, have found successful applications in many "winner-take-all" types of problems. This paper studies the dynamic stability properties of general Lotka-Volterra recurrent neural networks with delays. Conditions for nondivergence of the neural networks are derived. These conditions are based on local inhibition of networks, thereby allowing these networks to possess a multistability property. Multistability is a necessary property of a network that will enable important neural computations such as those governing the decision making process. Under these nondivergence conditions, a compact set that globally attracts all the trajectories of a network can be computed explicitly. If the connection weight matrix of a network is symmetric in some sense, and the delays of the network are in L2 space, we can prove that the network will have the property of complete stability.

Journal Article↗
PubMed2002

Four-month chemotherapy in the treatment of smear-negative pulmonary tuberculosis: results at 30 to 60 months.

INTRODUCTION: Most patients with active pulmonary tuberculosis (PTB) are treated with a 6-month short course regimen. The purpose of the present study was to assess the efficacy of using 4 months of chemotherapy to treat patients with smear-negative PTB. METHODS: A total of 314 patients were randomised to a daily or combined (daily and intermittent) regimen as follows: (1) 2HRZ/2HR--2 months of isoniazid (H), rifampicin (R) and pyrazinamide (Z), followed by 2 months of H and R or (2) 2HRZ/2H3R3--2 months of HRZ as in regimen 1, followed by H and R given 3 times weekly for 2 months or 4 months if initial sputum specimens were culture positive. RESULTS: One hundred and fifty-eight patients were assigned to the daily regimen and 156 to the combined regimen. Of the 158 patients, 99 had negative cultures and 59 had positive cultures. There was no relapse among 96 culture-negative patients assessed at 30 months and 68 patients at 60 months. However, 6 patients had no radiological response while 1 was considered on review to have non-tuberculous disease. There was no relapse among 57 culture-positive patients assessed at 30 months and 41 at 60 months. In the combined regimen group, 102 had negative cultures and 54 had positive cultures. There was 1 relapse in the culture-negative group of 100 patients assessed at 30 months and 74 at 60 months. There was no radiological response in 5 patients. One patient in the culture-positive group failed therapy but there were no relapses during follow-up to 60 months. CONCLUSION: A 4-month daily or combined regimen appears to be highly effective in the treatment of non-immunocompromised patients with smear- and culture-negative PTB.

Adolescent↗
PubMed2001

Composite control of a gyro mirror line-of-sight stabilization platform--design and auto-tuning.

In this paper, we propose a composite control scheme for a gyro mirror line-of-sight stabilization system. It comprises of an adaptive controller augmented with a variable structure (VS) to remain efficient in the face of modeling errors and extraneous disturbances. Under an adequate selection of control parameters, the control scheme guarantees an asymptotically stable closed-loop response. An automatic tuning method is developed for the proposed control scheme which explicitly uses inherent properties of the control structure for tuning purposes. Simulation and experimental results are provided to illustrate the operational principles of the proposed scheme and to demonstrate its viability in real practical applications.

Journal Article↗
PubMed2001

Acute epiglottitis in the tropics: is it an adult disease?

Acute epiglottitis has traditionally been described as a paediatric disease in reports from temperate countries. There have been very few reports from tropical countries. This is a retrospective review of 32 cases of acute epiglottitis from Singapore over an eight-year period from 1992 to 1999. There were 31 adults and only one child. In Singapore, Haemophilus influenzae Type b (Hib) immunization in not routine, and thus the increased prevalence in adults cannot be attributed to Hib immunization. Eleven patients required airway intervention, of whom nine had endotracheal intubation and two had a surgical airway. Significant predictors for airway intervention included the sex of the patient, stridor, presence of airway compromise on examination and a "thumb sign" on the lateral neck radiograph. In adults, selective airway intervention is recommended as those without airway compromise at presentation recover very well with medical treatment alone.

Acute Disease↗
PubMed2001

Physics-based approach to color image enhancement in poor visibility conditions.

Degradation of images by the atmosphere is a familiar problem. For example, when terrain is imaged from a forward-looking airborne camera, the atmosphere degradation causes a loss in both contrast and color information. Enhancement of such images is a difficult task because of the complexity in restoring both the luminance and the chrominance while maintaining good color fidelity. One particular problem is the fact that the level of contrast loss depends strongly on wavelength. A novel method is presented for the enhancement of color images. This method is based on the underlying physics of the degradation process, and the parameters required for enhancement are estimated from the image itself.

Journal Article↗
PubMed2000

Sphenochoanal polyps in Singapore: diagnosis and current management.

Sphenochoanal polyp is a rare form of choanal polyp. If unrecognised, they can be mistaken for an antrochoanal polyp. This will result in unnecessary exploration of the maxillary sinus, and a failure to remove the sphenoidal component of the sphenochoanal polyp. Adequate preoperative evaluation with computed tomography or magnetic resonance is mandatory to ascertain the correct diagnosis, and to facilitate the planning of the appropriate surgical procedure. We present two patients with sphenochoanal polyp and a review of the literature.

Adult↗
PubMed2000

Pneumonia presenting as acute abdomen in children: a report of three cases.

From 10th September 1998 till 5th June 1999, the Paediatric and Cardiothoracic Surgery Units of Sultanah Aminah Hospital Johor Bahru managed three children with lung collapse secondary to pneumonia. The dominant initial clinical presentation in all three cases was acute abdominal pain. Basal pneumonia was diagnosed in two cases post-operatively after surgical contributory causes were excluded intra-operatively. Thoracotomy, evacuation of infected debris and decortication of the collapsed lung was done in all three cases. In children presenting with acute abdominal pain, basal pneumonia should be considered as a possible contributory cause.

Abdomen, Acute↗
PubMed1999

Spontaneous subarachnoid haemorrhage and outcome--results from Tan Tock Seng Hospital, Singapore.

AIM OF STUDY: To ascertain the number of cases of spontaneous (aneurysmal) subarachnoid haemorrhage presenting to Tan Tock Seng Hospital, Singapore, over a one year period, the demographics of the patients involved, their treatment and their eventual outcome. METHOD: A retrospective study from June 1995 to June 1996. RESULTS: There were 62 patients admitted over this period with an average of 5 patients per month. Their ages ranged from 9 to 85 years with a mean of 54 years. All 62 patients underwent 4-vessel cerebral angiograms. Forty-three patients (69%) underwent clipping of their aneurysms. Twelve patients (19%) had negative angiograms. Four patients (6%) underwent coiling of their aneurysms via interventional neuroradiology techniques. Patients with subarachnoid haemorrhage of Grades 1 to 3 on the WFNS (World Federation of Neurological Surgeons) grading had a favourable outcome (Glasgow Outcome Score of 4 and 5) in 85% of the cases. The overall mortality rate for the operated group (all grades) was 11%. However for the group with good WFNS grading, namely the Grade 1 to 2 groups, there were no deaths. Twenty-four percent of patients developed clinically symptomatic vasospasm. Eighteen percent of patients required ventriculo-peritoneal shunting for hydrocephalus secondary to the subarachnoid haemorrhage. The overall management mortality (operated and non-operated cases) was 14% for proven aneurysmal and angiographically-negative spontaneous subarachnoid haemorrhage. These results are comparable to that of other reputable centers reported in the literature.

Adolescent↗
PubMed1998

Differential localisation of the metabotropic glutamate receptor mGluR1a and the ionotropic glutamate receptor GluR2/3 in neurons of the human cerebral cortex.

Specimens of human cerebral cortex were obtained during neurosurgical operations and studied by immunocytochemistry and electron microscopy, using antibodies to the metabotropic glutamate receptor subunit mGluR1a and the ionotropic glutamate receptor GluR2/3. A small number of non-pyramidal neuronal cell bodies were labelled for mGluR1a. Double immunolabelling with mGluR1a and GluR2/3 showed that most pyramidal cell bodies were labelled for GluR2/3 but not for mGluR1a. Despite the non-colocalisation of these two receptor subtypes in cell bodies, however, many dendrites and dendritic spines were double-labelled for mGluR1a and GluR2/3 at electron microscopy. As there is evidence that most neurons positive for GluR2/3 are pyramidal cells, this suggests that mGluR1a is present in dendrites of pyramidal neurons, despite absent or low levels of immunoreactivity in their cell bodies.

Adolescent↗
PubMed1998

A study on the efficacy of intraventricular urokinase in the treatment of intraventricular haemorrhage.

Twenty-one patients with intraventricular haemorrhage were randomized to two treatment groups. Both groups had bilateral external ventricular drains inserted, but only the treatment group received 50,000 IU urokinase instilled into the ventricles. The clinical and radiological progress, and 1- and 6-month outcomes were compared. The group that received urokinase treatment was shown to have an improved outcome, with a lower mortality and a lower incidence of hydrocephalus requiring shunt insertion. No haemorrhagic complications were seen in either group, although the treatment group had a slightly increased rate of drain-related ventriculitis.

Adult↗
PubMed1998

A prospective review of laparoscopic cholecystectomy in Brunei.

Brunei has a small population and a unique medical setup: The number of laparoscopic cholecystectomies (LCs) performed in our institution represents the total number of cases performed in this country. A prospective analysis of all the LCs performed in Brunei is presented. All 220 LCs performed between February 1, 1992, and November 30, 1996, were prospectively recorded on a detailed protocol. Analyses were made with respect to preoperative patient demography, intraoperative complications, and postoperative morbidity and mortality. Symptomatic gallstone disease was found to be common among the ethnic Nepalese population. In this series, nine patients required conversion to open surgery (4%). Acute cholecystitis comprised 21% of cases, and the mean operating time was longer in these cases (144.1 min) than in elective cases (101.2 min; P = 0.002). The overall morbidity was 5% with one ductal injury (0.5%). The mortality rate in this series was 0.5%. Our results of LC are favorable and comparable with those of published series. We conclude that LC has been successfully introduced into our institution. This study also represents an unofficial audit of the state of development of LC in Brunei.

Acute Disease↗
PubMed1998

Otitis externa--the clinical pattern in a tertiary institution in Singapore.

Otitis externa is a common condition in the tropics. Most of the data related to the condition have arisen from Western sources. Locally, the aetiology and the pathogens identified have not been systematically studied. A prospective study involving 107 patients was conducted. Otomycosis was frequently encountered. Coagulase negative Staphylococcus and Aspergillus niger were the most common bacteria and fungus cultured respectively. Gentamicin and polymyxin B were the most effective topical agents against Pseudomonas aeruginosa. Self-cleaning of the ears was the most common predisposing factor.

Adolescent↗
PubMed1998

Subclavian-oesophageal fistula as a complication of foreign body ingestion: a case report.

Foreign bodies in the upper aerodigestive tract are very common. In the local community, the commonest foreign body encountered in the oesophagus is the fish bone. Impaction in the thoracic oesophagus can lead to perforation and the subsequent formation of an arterial-oesophageal fistula. Such fistulae are inevitably aorto-oesophageal in nature. A subclavian-oesophageal fistula is described in this patient.

Animals↗
PubMed1998

Outcome of patients with traumatic brain injury managed on a standardised head injury protocol.

A standardised protocol in the management of severe head injury in our hospital enables pre-determined critical care-paths and consistent treatment regimes to be instituted. In Singapore there has been no previously reported data on the outcome of severely head injured patients. Over a 6-month period, 48 consecutive patients who were enrolled in our severe head injury protocol were prospectively studied. In addition to demographic and outcome data, physiologic measurements obtained from a computerised patient information system (Carevue Hewlett-Packard 9000) were analysed to determine the mean cerebral perfusion pressure (CPP) and intracranial pressure (ICP) achieved throughout the protocol period. Median Glasgow Coma Score for all patients on admission to the protocol was 6 (range 4 to 8). The mean age was 34.46 +/- 15.03 years with a male to female ratio of 43:5. The average duration of treatment on the protocol was 110.73 hours. Initial ICP measured was 25.5 +/- 19.68 mmHg. Outcome was measured at 6 months post-injury using the Glasgow Outcome Score. Favourable outcome (GOS 4-5) was seen in 29 of 48 patients (60.4%) while 12 out of 48 (25%) had an unfavourable outcome. There was a mortality of 14.6% (7 of 48 patients). Patients who survived had a higher mean CPP (P = 0.00005), a lower initial ICP and a mean ICP (P = 0.007 and 0.0009). The use of a protocol with standardised treatment goals in the management of traumatic brain injury allows for the optimal use of limited resources and provides consistency in treatment. Good outcome is related to early aggressive resuscitation to prevent hypotension and hypoxia, prompt evacuation of surgical mass lesions and the maintenance of an adequate cerebral perfusion pressure. Our results are comparable with that reported in other established neurotrauma systems.

Accidents↗