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Biomedical subjects

C Kwon

Publications and source records attributed to C Kwon.

At least 19 recordsLinked to original sources
PubMed2001

Ultrafast conductivity dynamics in colossal magnetoresistance manganites.

Ultrafast picosecond measurements of optically induced changes in the absolute conductivity (0.4-1.0 THz) of La0.7M0.3MnO3 thin films ( M = Ca, Sr) from 10 K to approximately 0.9 Tc reveal a two-component relaxation. A fast, approximately 2 ps, conductivity decrease arises from an optically induced modification of the effective phonon temperature. The slower component, related to spin-lattice relaxation, has a lifetime that increases upon approaching Tc from below in accordance with an increasing spin specific heat. We show that, for T<<Tc, partial differential sigma/ partial differential T is primarily determined by thermally disordered phonons while spin fluctuations dominate near Tc.

Journal Article↗
PubMed2001

Automatic activation of positive but not negative attitudes after traumatic brain injury.

This study investigated social judgment problems of an individual (AM) with bilateral frontal and temporal lobe damage including damage to the amygdala. We hypothesized that AM could automatically process positive, but not negative evaluative information and could process both types of evaluative information using controlled processing. In Phase 1 of Experiment 1 AM and controls were shown a series of words one at a time and were required to make good/bad judgments as quickly as possible. Results showed that AM was more likely than controls to rate words as good, and was significantly slower to make good/bad judgments of negatively, but not positively, evaluated words. In Phase 2 AM was shown a prime (positive or negative) then target (positive or negative) and instructed to evaluate whether the target word was good or bad. Results showed that AM responded more quickly when prime and target were both positive, but not when prime and target were both negative, whereas controls showed both types of priming. Experiment 2 determined whether AM's impaired processing of negative evaluative information could be abolished under controlled processing. AM was explicitly instructed to generate positive and negative connotations of a series of single words and given essentially unlimited time. Under these conditions, AM and controls did not differ significantly in their ability to generate positive versus negative connotations of words. In Experiment 3 AM and controls both showed normal semantic priming effects. The results are interpreted within the component process model of memory.

Adult↗
PubMed2000

The magnitude and challenge of false-positive newborn screening test results.

OBJECTIVES: This study examined for the first time to our knowledge the national data available from newborn screening programs in the United States and determined the salient characteristics of various screening tests for 3 hereditary metabolic disorders and 2 congenital endocrinopathies with emphasis on positive predictive values (PPVs) to delineate the magnitude of false-positive results. METHODS: Reports published by the Council of Regional Networks for Genetic Services for 1990 through 1994 were examined carefully, paying particular attention to phenylketonuria, galactosemia, biotinidase deficiency, congenital hypothyroidism, and congenital adrenal hyperplasia (CAH). Because of recent improvements in data collecting, reporting, and tabulating, we used data from 1993 and 1994 to determine the apparent sensitivity, specificity, relative incidence rates, and PPVs for the 5 disorders. For biotinidase deficiency and CAH, we also calculated relative incidence rates and PPVs for 1991 and 1992. RESULTS: Our analyses revealed the following best estimates for the relative incidence rates of 5 disorders: phenylketonuria, 1:14,000; galactosemia, 1:59,000; biotinidase deficiency, 1:80,000; congenital hypothyroidism, 1:3,300; and CAH, 1:20,000. An apparent sensitivity of 100% has been reported by the various states for most of the disorders, and specificity levels are all above 99%. The PPVs, however, range from 0.5% to 6.0%. Consequently, on average, there are more than 50 false-positive results for every true-positive result identified through newborn screening in the United States. CONCLUSIONS: The magnitude of false-positive results generated in newborn screening programs, particularly for congenital endocrinopathies, presents a great challenge for future improvement of this important public health program. Attention must be given to improved laboratory tests, use of more specific markers, and better risk communication for families of patients with false-positive test results.

Adrenal Hyperplasia, Congenital↗
PubMed1999

Orally bioavailable nonpeptide vitronectin receptor antagonists containing 2-aminopyridine arginine mimetics.

A peptide RGD analog containing a novel 2-aminopyridine arginine mimetic was discovered to have good affinity and selectivity for the vitronectin receptor. Incorporation of the 2-aminopyridine arginine mimetic into the 3-oxo-1,4-benzodiazepine-2-acetic acid integrin antagonist series led to novel and potent nonpeptide vitronectin receptor antagonists with promising levels of oral bioavailability.

Administration, Oral↗
PubMed1999

Brain O2 consumption and glutamate release during hypoglycemic coma in piglets are temperature sensitive.

Hypoglycemic injury in the mature brain is mediated by excitotoxicity, which is worsened by disordered cellular energy metabolism. The role of excitotoxicity in relation to brain energy metabolism during hypoglycemia has not been studied in the immature brain. Brain oxygen consumption (CMRO2) increases during hypoglycemia in piglets, whereas CMRO2 decreases in adult pig models. We tested the hypothesis that increased CMRO2 during hypoglycemic coma is temperature dependent and coincides with increased excitatory amino acids (EAA). We measured cerebral blood flow (CBF), CMRO2, and cortical microdiaysate EAA in pentobarbital-anesthetized piglets during hypoglycemic coma and during 2 h of recovery and in normoglycemic controls. In warmed animals brain temperature was kept normothermic (38.5 degrees C). In unwarmed animals brain temperature was allowed to fall (37.6 degrees C). During hypoglycemia CBF increased similarly in warmed animals and unwarmed animals; CMRO2 increased in warmed animals but not unwarmed animals. Glutamate increased during coma and increased more in warmed animals than unwarmed animals but normalized quickly during recovery. EEG recovered earlier in unwarmed animals. We conclude that during a hypoglycemic coma in the immature brain, CMRO2 and glutamate are increased in a temperature-dependent manner.

Animals↗
PubMed1998

Blood pressure in children exposed prenatally to cocaine.

Prenatal exposure to cocaine may alter autonomic nervous system function resulting in hypertension. Blood pressure was measured oscillometrically in a convenience sample of cocaine-exposed (n = 32) and nonexposed (n = 23) children, aged 8 to 26 months, by examiners unaware of exposure status. The exposed and nonexposed groups did not differ in systolic pressure (mean +/- SD 102.3 +/- 9.9 mmHg vs 119.1 +/- 19.4). Prenatal exposure to cocaine does not appear to be associated with elevated blood pressure in young children.

Autonomic Nervous System↗
PubMed1996

Structure-activity relationships of novel hematoregulatory peptides.

Hematopoiesis is a lifelong cell renewal process regulated by a family of lineage specific hematopoietic growth factors. Several hematopoietic growth factors such as G-CSF, GM-CSF, and M-CSF have been clinically evaluated for enhancement of host defense in normal and immunocompromised patients and for the treatment of infectious diseases. This paper reports the structure-activity relationships of low molecular weight hematoregulatory peptides based on a nonapeptide (1, SK&F 107647). Like the macromolecular growth factors, these peptides modulate host defense. A molecular target for this class of compounds has not yet been identified. However, the structure-activity relationships established by this study implicate a very specific molecular recognition event that is pivotal for the biological activities of 1 and its analogues.

Amino Acid Sequence↗