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Biomedical subjects

S Baek

Publications and source records attributed to S Baek.

16 recordsLinked to original sources
PubMed2007

Stress-strain behavior of the passive basilar artery in normotension and hypertension.

Vascular cells are very responsive to even subtle changes in their local mechanical environment, thus there is a pressing need to quantify normal states of stress and strain as well as any perturbations from these normal states. Toward this end, we must quantify constitutive behaviors for both normal and adapted (maladapted) arteries. In this note, we report the first quantification of changes in the biaxial mechanical behavior of the passive basilar artery due to hypertension.

Basilar Artery↗
PubMed2006

High friction from a stiff polymer using microfiber arrays.

High dry friction requires intimate contact between two surfaces and is generally obtained using soft materials with an elastic modulus less than 10 MPa. We demonstrate that high-friction properties similar to rubberlike materials can also be obtained using microfiber arrays constructed from a stiff thermoplastic (polypropylene, 1 GPa). The fiber arrays have a smaller true area of contact than a rubberlike material, but polypropylene's higher interfacial shear strength provides an effective friction coefficient of greater than 5 at normal loads of 8 kPa. At the pressures tested, the fiber arrays showed more than an order of magnitude increase in shear resistance compared to the bulk material. Unlike softer materials, vertical fiber arrays of stiff polymer demonstrate no measurable adhesion on smooth surfaces due to high tensile stiffness.

Journal Article↗
PubMed2006

A theoretical model of enlarging intracranial fusiform aneurysms.

The mechanisms by which intracranial aneurysms develop, enlarge, and rupture are unknown, and it remains difficult to collect the longitudinal patient-based information needed to improve our understanding. We submit, therefore, that mathematical models hold promise by allowing us to propose and test competing hypotheses on potential mechanisms of aneurysmal enlargement and to compare predicted outcomes with limited clinical information--in this way, we may begin to narrow the possible mechanisms and thereby focus experimental studies. In this paper, we present a constrained mixture model of evolving thin-walled, fusiform aneurysms and compare multiple competing hypotheses with regard to the production, removal, and alignment of the collagen that provides the structural integrity of the wall. The results show that this type of approach has the capability to infer potential means by which lesions enlarge and whether such changes are likely to produce a stable or unstable process. Such information can better direct the requisite histopathological examinations, particularly on the need to quantify collagen orientations as a function of lesion geometry.

Animals↗
PubMed2005

Histological evidence for the role of mechanical stress in modulating thermal denaturation of collagen.

The hyperthermia and thermal denaturation literatures reveal a time-temperature equivalency when heating cells or connective tissues: thermal damage increases with increasing temperature (for the same duration) and increases with increasing duration (for the same temperature). Recent findings conversely suggest that increasing the mechanical loading on a tissue during heating decreases the thermal damage (for a given temperature and duration of heating). Surprisingly, however, there are few histological correlates of such damage. In this paper, we show that progressive light microscopic changes - swelling of collagen bands, thickening of collagen-rich layers, hyalinization, and loss of birefringence approximately - correlate very well with both increased heating times and decreased mechanical loading. Increased mechanical stress is thus thermally protective and should be considered in the design of clinical procedures that use heating to treat diseases or injuries.

Animals↗
PubMed2005

Single-mode plane-polarized ytterbium-doped large-core fiber laser with 633-W continuous-wave output power.

We demonstrate a cladding-pumped single-mode plane-polarized ytterbium-doped fiber laser generating 633 W of continuous-wave output power at 1.1 microm with 67% slope efficiency and a polarization extinction ratio better than 16 dB. The laser is end pumped through both fiber ends and shows no evidence of roll-over, even at the highest output power, which is limited only by the available pump power.

Journal Article↗
PubMed2005

Heat-induced changes in the finite strain viscoelastic behavioir of a collaagenous tissue.

Supra-physiological temperatures are increasingly being used to treat many different soft need for injuries. To identify improved clinical treatments, however, there is a need for better information on the effect of the mechanics on the thermal damage process as well as the effect of the incurred damage on the subsequent mechanical properties. In this paper we report the first biaxial data on the stress relaxation behavior of a collagenous tissue before and after thermal damage. Based on a two-dimensional finite strain viscoelastic model, which incorporates an exponential elastic response, it is shown that the thermal damage can significantly decrease the characteristic time for stress relaxation and the stress residual.

Animals↗
PubMed2001

Synthesis and antibacterial activity of 2-substituted 6-fluoro-1,4-dihydro-4-oxo-3-quinolinecarboxylic acids.

A series of 2-substituted 6-fluoro-1,4-dihydro-4-oxo-3-quinolinecarboxylic acids was prepared and evaluated for antibacterial activity. The 6-fluoro-2-methyl-1-prenyl-1,4-dihydro-7-(3,5-dimethylpiperazinyl)-4-oxo-3-quinolinecarboxylic acid (14f) exhibited the most potent antibacterial activity against gram-positive bacteria among the total 32 derivatives. The synthetic strategies involve the use of well known keto ester condensation of benzoyl chloride and reductive cyclization of intermediates (4a-d) to afford 4-hydroxy-1,2-dihydro-2-oxo-quinoline derivatives (5a,b) or 1-hydroxy-1,4-dihydro-4-oxo-quinoline derivatives (6a,b).

Anti-Bacterial Agents↗
PubMed2001

Optimal operational factors for nitrite accumulation in batch reactors.

The environmental factors that affected the accumulation of nitrite in nitrifying reactors were investigated using a mixed culture. A batch reactor with 50 mg-N/l of ammonia was used. The pH, temperature and dissolved oxygen concentration were varied. The concentration of unionized free ammonia also changed with the oxidation of ammonia and the variation of pH and temperature. The accumulation of nitrite was affected sensitively by pH and temperature. A higher nitrite concentration was observed at pH 8-9 or temperature around 30 degrees C. The dissolved oxygen also affected, giving the highest nitrite accumulation at around 1.5 mg/l. These were the favored conditions for nitrite production. The free ammonia concentration influenced the nitrite accumulation also, by inhibiting nitrite oxidation. The inhibition became apparent at a concentration of approximately 4 mg/l or above, but insignificant at below 1 mg/l. Thus, simultaneously high free ammonia concentration and maximum specific ammonia-oxidation rate (above 15 x 10(-3) mg-N/mg-VSS x h) were needed for a significant nitrite accumulation. When the two conditions were met, then the highest accumulation was observed when the ratio of the maximum specific oxidation rate of ammonia to the maximum specific oxidation rate of nitrite (ka/kn) was highest. Under the optimal operating conditions of pH 8, 30 degrees C and 1.5 mg/l of dissolved oxygen, as much as 77% of the removed ammonia accumulated in nitrite.

Algorithms↗
PubMed2001

Guidewire incidents with inferior vena cava filters.

Several authors have demonstrated that prophylactically inserted inferior vena cava filters have decreased pulmonary thromboembolic complications in selected high-risk trauma patients. Guidewire-related mishaps are potential complications of inferior vena cava filters and are likely underreported. The authors present two cases and review strategies to prevent these complications.

Aged↗
PubMed2000

Failure to induce inhibition of cyclin A and up-regulation of p21 expression in phorbol ester-resistant U937 cells by phorbol ester.

Differentiation resistant U937 cells were derived from parental U937 cells by selecting for continuously growing U937 cells in cell cultures continuously exposed to phorbol 12 myristate 13-acetate (PMA). Unlike in other known PMA resistant U937, the basal expression of protein kinase C (PKC) isozymes in these PMA resistant cells (R-U937) was significantly decreased. Subsequent analyses revealed differences between the wild type U937 and the R-U937 cells with respect to G1 phase arrest, which seemed to occur in U937 because of low levels of cdk2 kinase activity. This abolished cdk2 kinase activity is mainly due to inhibition of cdk2 phosphorylation, cyclin A down-regulation and cyclin dependent kinase inhibitor p21 up-regulation. Our data suggest that events down-stream of PKC activation may mediate cell cycle control. Thus, the R-U937 cells could be useful for further PKC mediated cell cycle control studies.

Blotting, Western↗
PubMed1998

Gene therapy for restenosis: getting nearer the heart of the matter.

Intensive work over the past decade has been directed to the study of vascular gene transfer as an approach to the unresolved problem of restenosis. This effort has resulted in a significant foundation of knowledge relative to the activities of potentially therapeutic gene products as well as the capabilities and limitations of vector systems and mechanical delivery modalities available for effecting the vascular expression of these gene products. In several instances, significant progress has been made by experiments highlighting unexpected difficulties and the need for more comprehensive understanding. It is thus now possible to clearly define and address specific challenges that must be overcome in order to make feasible progress from the preclinical to the clinical arena. The key challenges at present appear to include the evolution of clinically practical delivery methods that meet the kinetic requirements of achieving efficient gene transduction and the availability of vectors that maximize efficiency while minimizing undesirable host responses. Emerging data suggest that approaches to solving each of these issues may have recently been developed. Basic research evaluating these new delivery mechanisms and molecular vectors is essential to establish their true potential for use in the clinical arena.

Animals↗
PubMed1996

Syme amputation: results in patients with severe forefoot ischemia.

Since 1980, 35 patients (age range 40-77 years) with severe forefoot ischemia have undergone a unilateral Syme amputation. Thirty-one patients (89%) were diabetic. The indication for amputation was either extensive forefoot gangrene or ulceration too advanced for a digital or transmetatarsal amputation. Twenty-two amputations (63%) were immediately preceded by either percutaneous transluminal angioplasty (four) or a bypass procedure to the popliteal artery (five) or an infrapopliteal artery (13). Primary healing occurred in 19 (86%) of 22 amputations immediately preceded by revascularization and in 10 (77%) of 13 limbs undergoing amputation alone. Twenty-eight (97%) of the 29 patients with successful primary healing were successfully rehabilitated. Rehabilitation rendered 13 patients fully ambulatory, 15 ambulatory with intermittent use of a walker or cane and one unable to walk. At follow-up of four months to 13 years (mean 42 months), the cumulative ambulatory rate at 1, 3, and 5 years was 92, 80 and 80%, respectively. Syme amputation allows a return to a functional ambulatory status in a high percentage of patients with severe forefoot ischemia. These findings suggest that Syme amputation is an acceptable option in dysvascular patients with severe forefoot ischemia.

Adult↗
PubMed1996

Directional loading of the kinesin motor molecule as it buckles a microtubule.

Single kinesin motor molecules were observed to buckle the microtubules along which they moved in a modified in vitro gliding assay. In this assay a central portion of the microtubule was clamped to the glass substrate via biotin-streptavidin bonds, while the plus end of the microtubule was free to interact with motors adsorbed at low density to the substrate. A statistical analysis of the length of microtubules buckled by single motors showed a decreasing probability of buckling for loads greater than 4-6 pN parallel to the filament. This is consistent with kinesin stalling forces found in other experiments. A detailed analysis of some buckling events allowed us to estimate both the magnitude and direction of the loading force as it developed a perpendicular component tending to pull the motor away from the microtubule. We also estimated the motor speed as a function of this changing vector force. The kinesin motors consistently reached unexpectedly high speeds as the force became nonparallel to the direction of motor movement. Our results suggest that a perpendicular component of load does not hinder the kinesin motor, but on the contrary causes the motor to move faster against a given parallel load. Because the perpendicular force component speeds up the motor but does no net work, perpendicular force acts as a mechanical catalyst for the reaction. A simple explanation is that there is a spatial motion of the kinesin molecule during its cycle that is rate-limiting under load; mechanical catalysis results if this motion is oriented away from the surface of the microtubule.

Animals↗
PubMed1995

Concurrent abdominal aortic aneurysm and urologic neoplasm: an argument for simultaneous intervention.

This report describes the surgical management of 24 patients with concurrent abdominal aortic aneurysm (AAA) and urinary tract neoplasm. The patient population consisted of 22 men and two women whose average age was 65.5 years. AAA sizes ranged from 3.1 to 9.0 cm (mean 5.2 cm) in diameter. Urinary tract neoplasms included transitional cell carcinoma (TCC) of the bladder (n = 19), adenocarcinoma of the prostate (n = 3), and TCC of the renal pelvis (n = 2). Urologic procedures included radical prostatectomy, radical nephroureterectomy, and radical cystoprostatectomy with continent or ileal loop urinary diversion. The AAA was resected at the time of the urologic procedure in 12 patients (group I) or prior to the urologic procedure in five patients (group II) and was left in situ in seven patients (group III: AAA diameter 3.1 to 5.5 cm). All patients but one in group I recovered without complications. One patient developed an infection postoperatively as a result of fluid collection anterior to the aortic vascular graft; the fluid was successfully drained and the patient subsequently recovered uneventfully. All patients in group II had a marked retroperitoneal desmoplastic reaction at the time of the urologic procedure as a result of prior aneurysmectomy, which complicated the ureteral dissection. One patient later required an ileal ureteral reconstruction for obliterative fibrosis of the ureter. At a mean follow-up of 34 months, no infectious or mechanical complications of the vascular prosthesis occurred in group I or II. Eight patients in group I and two in group II are alive. Three have died of metastatic disease and two of myocardial infarction. Of the seven patients in group III, four subsequently required AAA resection for an increase in AAA size and three have died.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenocarcinoma↗
PubMed1976

Benign liver cell adenoma associated with use of oral contraceptive agents.

A benign hepatic adenoma in a young woman taking oral contraceptives for 7 years is reported. The diagnosis must be suspected in any young woman taking oral contraceptive agents who develop signs and symptoms of acute cholecystitis with hepatomegaly or mass, or when signs and symptoms of non-traumatic intraabdominal hemorrhage are present. Rupture of the tumor is a life-threatening complication. Treatment should be either hepatic lobectomy or wide local resection.

Adult↗