Correcting for accidental correlations in saturated avalanche photodiodes

In this paper we present a general method for estimating rates of accidental coincidence between a pair of single photon detectors operated within their saturation regimes. By folding the effects of recovery time of both detectors and the detection circuit into an "effective duty cycle" we are able to accomodate complex recovery behaviour at high event rates. As an example, we provide a detailed high-level model for the behaviour of passively quenched avalanche photodiodes, and demonstrate effective background subtraction at rates commonly associated with detector saturation. We show that by post-processing using the updated model, we observe an improvement in polarization correlation visibility from 88.7% to 96.9% in our experimental dataset. This technique will be useful in improving the signal-to-noise ratio in applications which depend on coincidence measurements, especially in situations where rapid changes in flux may cause detector saturation.

Obesity prevention and management: Singapore's experience

Singapore's obesity prevalence among adult Singapore residents aged 18-69 increased from 6.9% (2004) to 10.8% (2010). Among school-going children, the prevalence of overweight and severely overweight (body weight > 120% standard weight for height) increased from 1.4% (1976) to 12.7% (2006) for primary 1 students, and 2.2% to 15.9% for primary 6 students. Fundamentally, obesity is a function of excess energy intake (food consumption) and insufficient energy expenditure (physical activity). In 2010, about 40% did not have sufficient physical activity, and about 60% consumed excess energy. For students in the mainstream schools, only a fifth consumed at least two servings of fruits and vegetables every day, and a tenth were physically active for at least 60 min on 5 or more days a week. From a public health perspective, the most powerful levers for influencing population health lie in interventions that make healthy living convenient and an unconscious choice by targeting the social and environmental context. Recognizing this, the Health Promotion Board has in recent years made a strategic shift away from just public education campaigns aimed at individual behaviours, to focus on creating a ground-up social movement to enable and empower individuals to live out a healthy lifestyle.

Enhancing image contrast using coherent states and photon number resolving detectors

We experimentally map the transverse profile of diffractionlimited beams using photon-number-resolving detectors.We observe strong compression of diffracted beam profiles for high detected photon number. This effect leads to higher contrast than a conventional irradiance profile between two Airy disk-beams separated by the Rayleigh criterion.

Heralded, pure-state single-photon source based on a Potassium Titanyl Phosphate waveguide

We analyze the generation of single spatial mode, spectrally uncorrelated photon pairs via type II spontaneous parametric down-conversion in a Potassium Titanyl Phosphate (KTP) waveguide using real experimental parameters. We show that this source can be used as an efficient, heralded, pure-state single-photon source.

Identification of alkylidene hydrazides as glucagon receptor antagonists

High throughput screening of our small molecule combinatorial library identified a class of benzoylnaphthalenehydrazones with modest affinity for the human glucagon receptor. Optimization of this initial hit through a series of targeted libraries and traditional medicinal chemistry led to ligands with nanomolar affinities. Pharmacological evaluation demonstrated that these ligands were competitive glucagon receptor antagonists. Intravenous administration of a representative benzoylnaphthalenehydrazone into rats attenuated glucagon-stimulated glucose levels.

Intracellular pH on translocation of protein kinase C isozymes in rat pinealocytes

In rat pinealocytes, cytoplasmic alkalization causes protein kinase C (PKC) translocation, but the isozyme involved is not known. In this study, we investigated the effect of cytoplasmic alkalization on membrane-associated PKCalpha, delta, epsilon, and zeta, four isozymes present in the rat pineal gland. Treatment with NH(4)Cl, which had no effect on PKCzeta, caused a sustained increase in membrane-associated PKCalpha, delta, and epsilon that lasted for at least 60 min. The effect of NH(4)Cl on PKCalpha, delta, and epsilon was reduced by sodium propionate, an agent that counteracts the effect of NH(4)Cl on intracellular pH. Both sodium propionate and 5-(N,N-hexamethylene)amiloride (HMA), two treatments that abolished the effect of norepinephrine on cytoplasmic alkalization, also reduced norepinephrine-mediated increases in membrane-associated PKCalpha, delta, and epsilon. In contrast, these two treatments did not have an effect on the increase in membrane-associated PKC isozymes caused by 4beta-phorbol 12-myristate 13-acetate (PMA), an active phorbol ester, even though HMA was effective in abolishing PMA-mediated increases in intracellular pH. These results, apart from demonstrating that cytoplasmic alkalization by itself can cause translocation of PKCalpha, delta, and epsilon in rat pinealocytes, also indicate that the norepinephrine-stimulated cytoplasmic alkalization plays an important role in transducing signals from the adrenergic receptor to selective PKC isozymes. However, PKC translocation stimulated directly by PMA does not appear to be sensitive to changes in intracellular pH.

Mastocytosis: magnetic resonance imaging patterns of marrow disease

OBJECTIVE

To report the bone marrow MRI findings of patients with mastocytosis and correlate them with clinical, pathologic, and radiographic features.

DESIGN AND PATIENTS

Eighteen patients with mastocytosis had T1-weighted spin echo and short tau inversion recovery MRI of the pelvis at 0.5 T. In each patient the MR pattern of marrow disease was classified according to intensity and uniformity and was correlated with the clinical category of mastocytosis, bone marrow biopsy results, and radiographic findings.

RESULTS

Two patients had normal MRI scans and normal bone marrow biopsies. One patient had a normal MRI scan and a marrow biopsy consistent with mastocytosis. Fifteen patients had abnormal MRI scans and abnormal marrow biopsies. There were several different MR patterns of marrow involvement; none was specifically associated with any given clinical category of mastocytosis. Fifteen of the 18 patients had radiographs of the pelvis; of those, 13 with abnormal MRI scans and abnormal marrow biopsies had the following radiographic findings: normal (nine); sclerosis (three); diffuse osteopenia (one).

CONCLUSION

While radiographs are very insensitive for the detection of marrow abnormalities in mastocytosis, MRI is very sensitive and may display several different patterns of marrow involvement.

Systemic mastocytosis: CT and US features of abdominal manifestations

PURPOSE

To study the imaging findings in patients with systemic mastocytosis and to correlate the findings with the severity of disease on the basis of an established classification system. Pathologic findings, when available, were correlated with imaging findings.

MATERIALS AND METHODS

Computed tomographic (CT) and ultrasound (US) scans and corresponding pathologic findings, when available, were retrospectively reviewed in 27 patients with systemic mastocytosis.

RESULTS

Only five (19%) of the patients in our series had normal abdominal CT and/or US examination results. Common abdominal imaging findings associated with systemic mastocytosis were hepatosplenomegaly, retroperitoneal adenopathy, periportal adenopathy, mesenteric adenopathy, thickening of the omentum and the mesentery, and ascites. Less common findings included hepatofugal portal venous flow, Budd-Chiari syndrome, cavernous transformation of the portal vein, ovarian mass, and complications such as chloroma. The findings were more common in patients with category II and those with category III disease.

CONCLUSION

Abdominal findings at CT and US are common in patients with systemic mastocytosis. Although the findings in patients with systemic mastocytosis are not specific to the disease, they are useful in directing further studies for diagnostic confirmation and in estimating the extent of systemic involvement.

Role of tissue diagnosis in pulmonary involvement in pediatric human immunodeficiency virus infection

BACKGROUND

Pulmonary complications occur commonly during HIV infection. The aim of this study was to evaluate the clinical value of lung tissue examination in the diagnosis and treatment of pulmonary disorders in children with HIV infection.

METHODS

The medical records of 347 children enrolled between January, 1990, and April, 1994, into various antiretroviral therapy protocols were reviewed to identify patients who underwent a lung biopsy.

RESULTS

Fourteen patients underwent diagnostic lung biopsies on 16 separate occasions. The most common radiologic findings were nodular infiltrates which were localized in 7 patients and diffuse in 6. Eight patients presented with fever and progressive respiratory distress unresponsive to empiric therapy, whereas the rest had progressive nodular infiltrates. The pathologic diagnoses included opportunistic infection in 7 patients, lymphocytic interstitial pneumonitis in 5, non-Hodgkin's lymphoma in 3 and interstitial fibrosis in 1. The biopsy led to a major change in the treatment of 7 patients which resulted in a significant improvement of the pulmonary process in all of them. In an additional patient the excisional biopsy proved curative.

CONCLUSIONS

When patients are selected appropriately, lung biopsy might have a significant impact on therapy and outcome in HIV-infected children with pulmonary infiltrates.

Gaucher disease: abdominal MR imaging findings in 46 patients

Abdominal magnetic resonance imaging findings were reviewed in 46 patients with Gaucher disease. All patients had hepatosplenomegaly at the time of initial imaging. Splenic nodules were present in 14 patients (30%) and varied in signal intensity. These nodules were isointense on T1-weighted and hypointense on T2-weighted images. Splenic infarcts were seen in 15 patients (33%), and four of these patients (9%) also had subcapsular fluid collections. Both nodules and infarcts were present in the spleen in four patients (9%). Pathologic correlation was performed with specimens from two patients who underwent partial splenectomy. Focal areas of abnormal signal intensity were noted in the liver in nine patients (20%). They were either stellate or segmental, and may represent fibrotic septa with ischemic changes associated with aggregates of Gaucher cells. No changes were noted in the kidneys or abdominal lymph nodes.

Pulmonary metastases: MR imaging with surgical correlation--a prospective study

The sensitivity of magnetic resonance (MR) imaging for detection of pulmonary metastases in 11 patients scheduled for thoracotomy and curative resection of metastases was evaluated with a prospective, controlled study. MR imaging performed at 0.5 T was compared with chest radiography, computed tomography (CT), and thoracotomy in 12 cases. (One patient had two separate occurrences of pulmonary metastases.) All images were interpreted in blinded fashion. When all MR sequences were interpreted together, MR imaging enabled correct identification of all patients with pulmonary nodules (100%). CT enabled detection of at least one nodule in all 12 cases (100%) by design; the sensitivity of chest radiography was only 64%. For individual nodules, MR imaging was at least as sensitive as CT (P2 less than .25 [two-sided value]) and significantly more sensitive than chest radiography (P2 less than .01). Among all MR sequences, short inversion time inversion-recovery sequences had the highest sensitivity for detection of individual nodules (82%).

Residual coronary stenoses and calculated transstenotic gradients after intravenous streptokinase versus tissue plasminogen activator

To compare the relative success of intravenous streptokinase (STK) and tissue plasminogen activator (TPA) on the severity of residual infarct-related coronary stenoses, we evaluated 45 patients receiving thrombolytic therapy for acute myocardial infarction. Twenty-three patients (18 men and 5 women) received STK (1.5 million units), while 22 patients (18 men and 4 women) received TPA (100 mg) within 6 hours of chest discomfort. Cardiac catheterization was performed before hospital discharge (8 days) with quantitative coronary arteriography and estimation of transstenotic pressure gradients using fluid dynamic equations. Although angina pectoris was equally common (STK, 7 of 23 [30%] versus TPA, 5 of 22 [23%], p = NS), recurrent infarction (STK, 3 of 23 [13%] versus TPA, 7 of 22 [32%], p less than 0.05) and coronary angioplasty (STK, 2 of 23 [9%] versus TPA, 7 of 22 [32%], p less than 0.05) were more frequent in those receiving TPA. Infarct-related coronary patency was greater in TPA-treated subjects (STK, 15 of 23 [65%] versus TPA, 19 of 22 [86%], p less than 0.05), although minimum stenotic diameter (STK, 0.77 +/- 0.48 mm versus TPA, 0.57 +/- 0.38 mm, p less than 0.05), and calculated transstenotic pressure gradient (STK, 8.7 +/- 17.0 mm Hg versus TPA, 23.7 +/- 30.2 mm Hg, p less than 0.05) suggested severe residual stenosis. These effects were accentuated at elevated coronary flow velocities (8 to 20 cm/sec).(ABSTRACT TRUNCATED AT 250 WORDS)

Detection of ACTH-producing bronchial carcinoid tumors: MR imaging vs CT

Adrenocorticotrophic hormone (ACTH)-producing bronchial carcinoid tumors tend to occur in the middle third of the lung adjacent to pulmonary vessels. Because they cause signs and symptoms when quite small (by virtue of their ACTH production), they may not be detected by CT. MR imaging was performed in 10 consecutive patients with surgically proved ACTH-producing bronchial carcinoid tumors in order to test the ability of MR to clarify equivocal or indeterminate findings on CT examinations. All bronchial carcinoid tumors had high signal intensity on T2-weighted and short-inversion-time inversion-recovery images, facilitating their distinction from pulmonary vasculature. In eight patients, the CT and MR images were equivalent in the detection of bronchial carcinoid tumors. In two patients, MR showed tumors in the middle third of the lung that were equivocal on CT. MR imaging may distinguish small bronchial carcinoid tumors from adjacent pulmonary vessels in the central third of the lung at a time when the CT study is nondiagnostic or equivocal.

Detection of malignant bone tumors: MR imaging vs scintigraphy

One hundred six patients with a known or suspected diagnosis of bone cancer (11 patients with biopsy-proved primary tumors, 95 patients with metastatic disease) were evaluated with scintigraphy and MR imaging to determine the relative sensitivity of each technique in the detection of bone disease. MR imaging was performed at 0.5 T as part of the entry evaluation into Intramural Research Board protocols (30%), for evaluation of cord compression, or because of an equivocal scintigram. MR was performed with T1-weighted (e.g., 300-500/10-20 [TR/TE]), T2-weighted (e.g., 2000/80) spin-echo (SE), and a short-TI inversion recovery (STIR) pulse sequence. Scintigrams were performed with 99mTc-methylene diphosphonate. A retrospective analysis showed that in 30 (28%) of 106 patients, MR imaging performed over a limited region of interest revealed a focal abnormality consistent with tumor that was not observed on scintigraphy. Only one patient had an abnormality on scintigraphy, caused by a metastasis, that was not found on MR images. In 73 (69%) of the 106 patients, the results of MR imaging and scintigraphy were equivalent; in 41 cases results of both techniques were normal. A McNemar analysis of the discordant cases showed MR imaging to be more sensitive than scintigraphy was (p less than .001). Our results suggest that although MR imaging has a greater sensitivity in detecting focal disease, scintigraphy is still the most useful screening test for evaluating the entire skeleton. MR imaging should be reserved for clarification of scintigraphic findings when suspicion is high for tumor.

Development of ultrastructural specializations during the formation of acetylcholine receptor aggregates on cultured myotubes

The ultrastructure of cultured rat myotubes was examined at stages in the initial assembly of acetylcholine receptor (AChR) aggregates in order to elucidate the role of cell-surface specializations in aggregate formation. Within 4-6 hr, embryonic brain extract (EBX) induces the formation of sites of AChR density elevated 5-9 X above that of surrounding regions, and the appearance of these aggregates is preceded by the formation of clouds of punctate microaggregates (Olek et al., 1983). A video image-intensification system was used to monitor this redistribution of fluorescently labeled AChR, and sites of aggregation were mapped on identified myotubes. After processing the cultures for electron microscopy, thin sections were taken through identified aggregate sites at various stages in assembly. Specializations, including a basal lamina, mound-shaped plasma membrane contours with occasional deep infoldings, and a subjacent dense cytoskeletal specialization, which tended to exclude other cytoplasmic organelles, were associated with newly formed aggregates found 4-6 hr after adding EBX to the cultures. Analysis of random thin sections through EBX-treated and untreated myotubes showed that the extent of specializations of the basal lamina and cytoplasm was approximately threefold greater in cells exposed to EBX for 4 hr, suggesting a concurrent, and possibly interdependent, organization of such specializations with AChR aggregate assembly. Examination of sections through clouds of microaggregates, which formed within 90 min, revealed mound-shaped plasma membrane contours and underlying cytoplasm depleted of organelles but relatively little basal lamina and submembrane cytoskeletal density. These results suggest that the initial stage of AChR aggregate assembly involves relatively subtle changes in the structure of the cell cortex and that the evolution of microaggregates to aggregates may require the formation of additional cytoskeletal and extracellular matrix structures.

Properties of p-nitrophenyl phosphatase activity from porcine neutrophils

p-nitrophenyl phosphatase activity is high in porcine neutrophils and was found in plasma membrane and granule fractions isolated from sucrose density gradients after nitrogen cavitation to disrupt the cells. Very little activity was found in the cytosol. The enzyme has optimum activity at alkaline pHs with a pH optimum of 10.3. The pH profile was fairly broad with activity still remaining at physiological pH. Orthovanadate was shown to be a potent competitive inhibitor of the enzyme with a Ki of 14 microM. Phosphate also inhibited but at millimolar concentrations and the two inhibitors bind in a mutually exclusive fashion. Evidence from experiments using divalent ion chelators and zinc ions suggested that the phosphatase is a zinc metalloenzyme. Beryllium was found to be a very potent, non-competitive inhibitor of the neutrophil enzyme (Ki = 1.1 microM). Levamisole and theophylline were both shown to be uncompetitive inhibitors of the porcine phosphatase (Ki = 0.2 mM and 1.2 mM respectively). The neutrophil phosphatase was inhibited by L-homoarginine but unaffected by L-phenylalanine and L-glutamate.

Basilar-membrane motion in the alligator lizard: its relation to tonotopic organization and frequency selectivity

In the alligator lizard the entire basilar membrane is accessible for measurements of its velocity by the Mössbauer method. Tests of the method indicate (1) the Mössbauer source can be placed on the basilar membrane without altering the signal-transmission properties of the cochlea, and (2) the source adheres to the basilar membrane. Isovelocity curves (IVCs) were constructed by plotting (as a function of tone frequency) the sound-pressure level at the tympanic membrane required to produce a specified velocity amplitude. IVCs from 21 lizards for source locations spanning the length of the basilar membrane indicate that basilar-membrane velocity does not vary systematically with longitudinal location as it does in mammalian cochleas. Measurements of velocity waveforms in two lizards do not indicate substantial nonlinearity in the inner-ear mechanical system. The frequency dependence of the basilar-membrane velocity is similar to that of the extrastapes velocity over the range 0.4 to 2 kHz. Thus, the tonotopic organization and frequency selectivity, which have been previously demonstrated in this species in responses of both auditory-nerve fibers and cells of the receptor organ, are apparently not primarily determined by basilar-membrane motion.

Effect of metoclopramide on interdigestive myoelectric activity in the conscious dog

The effect of two-hour infusions of metoclopramide at five different doses on interdigestive intestinal electrical activity was studied in four conscious fasting dogs. Spike activity during the infusions was quantitatively compared with activity during preceding and following periods of saline infusion. The effect of the drug was the enhancement of spike activity during migrating myoelectric complexes (MMC) without disruption of the fasting pattern; the effect was most marked in the proximal small intestinal and diminished distally. As in other published studies with metoclopramide, its effects were variable and not dose dependent. The enhancement of the MMC by an exogenous stimulus, not previously reported, provides indirect evidence for cholinergic mediation of cyclical motor activity, and also suggests a rational basis for therapy.

Quantitative effect of oral feeding on gastrointestinal myoelectric activity in the conscious dog

Gastrointestinal myoelectric activity was recorded in seven studies in five dogs during two hours of fasting immediately followed by feeding and subsequent recording for four hours. In four studies serial plasma samples were taken for radioimmunoassay of insulin and gastrin. In all animals there was a significant reduction (P less than 0.01) in gastric basic electrical rhythm (BER) frequency on feeding which was sustained throughout the postprandial period. There was no change in the duodenal BER. Feeding induced a significant (P less than 0.01) increase in overall jejunal and ileal (but not duodenal) spike activity. Ileal (but not jejunal) spike activity again increased significantly (P less than 0.05) after the first two post-prandial hours. The changes in serum gastrin or in serum insulin did not appear to account for most of the observed changes in myoelectric activity, suggesting that other humoral and/or neural factors mediate the response to food.

Identification of synaptic acetylcholine receptor sites in retina with peroxidase-labeled alpha-bungarotoxin

An alpha-bungarotoxin-horseradish peroxidase conjugate, which binds specificity to nicotinic acetylcholine receptors, was synthesized. This conjugate was bound by 5-7% of the synapses in the inner plexiform layer of the chicken retina. Bipolar ribbon synapses as well as amacrine synapses bound the conjugate.

Detection and treatment of deafness in early infancy

Procedures for the detection and rehabilitation of very young deaf children developed by the McGill University Project for Deaf Children are described. The development of tests for screening new-born babies for hearing loss in maternity hospitals, well-baby clinics and pediatric care are reported and rehabilitation procedures for deaf children in early infancy are out-lined.