Biomedical subjects

A Akay

Publications and source records attributed to A Akay.

5 recordsLinked to original sources

PubMed2006

Near-irreversibility in a conservative linear structure with singularity points in its modal density.

Through two complementary approaches, using modal response and wave propagation, the analyses presented here show the conditions under which a decaying impulse response, or a nearly irreversible energy trapping, takes place in a linear conservative continuous system. The results show that the basic foundation of near-irreversibility or apparent damping rests upon the presence of singularity points in the modal density of dynamic systems or, analogously, in the wave-stopping properties associated with these singularities. To illustrate the concept of apparent damping in detail, a simple undamped beam is modified to introduce a singularity point in its modal density distribution. Simulations show that a suitable application of a compressive axial force to an undamped beam placed on an elastic foundation attenuates its impulse response with time and develops the characteristics of a nearly irreversible energy trap.

Journal Article↗

PubMed2002

Assessment of depression in subjects with psoriasis vulgaris and lichen planus.

AIM: The aim of this study was to investigate the frequency of depressive symptoms in psoriasis vulgaris and lichen planus and to evaluate the relationship between the Beck depression scores and the Psoriasis Area and Severity Index (PASI) scores of subjects with psoriasis vulgaris. SUBJECTS: The study involved 120 subjects attending the dermatology clinic of Izmir Ataturk Training Hospital (Izmir, Turkey) and comprised 50 subjects with psoriasis vulgaris, 30 with lichen planus and 40 healthy control subjects. RESULTS: Subjects with psoriasis vulgaris, lichen planus and controls had depression scores of 58%, 53% and 20%, respectively. The Beck depression scores of patients with psoriasis vulgaris were significantly higher than those of the control group. The PASI scores showed a correlation with Beck depression scores. Smoking and drinking were very common in subjects with psoriasis vulgaris. There was no correlation between the duration of illness and depressive symptoms. CONCLUSIONS: This study confirms the importance of depressive symptoms in two common dermatological diseases. It is important to recognize this association as it affects both clinical outlook and response to treatment.

Adult↗

PubMed2002

Calcinosis cutis universalis.

We report the case of a 49-year-old female who complained of hardening of the skin, with onset about 1.5 years before presentation. The laboratory data showed normal biochemistry profile. Routine haematochemical examinations showed slight anaemia, an increased erythrocyte sedimentation rate and negative rheumatological markers. Calcium excretion in a 24-h urine sample was normal, but the phosphate excretion was slightly low. The clinical diagnosis was verified by soft tissue ultrasound examination showing subcutaneous calcifications. X-ray examination of bones evidenced no abnormal calcification. Mammography revealed deep seated bilateral reticular calcifications, even in the axillary region. Histological examination showed calcinosis cutis. On these grounds, the diagnosis of idiopathic universal calcinosis cutis was made. The authors describe the clinical and histological picture and discuss the laboratory findings.

Calcinosis↗

PubMed2000

Dissipation in solids: thermal oscillations of atoms

Dissipation in solids describes conversion of kinetic energy to thermal energy. Heat capacity of a solid relates to the kinetic energy of the oscillations of its atoms with the assumption that they are in thermal equilibrium. Previous studies investigated criteria related to thermal relaxation, the process by which thermal equilibrium is established. They examined conditions for irreversible distribution of energy among the modes of a nonlinear periodic structure that represents atoms in a solid. These studies all point to the chaotic behavior of a freely vibrating nonlinear lattice as the kernel of the problem in addressing thermal relaxation. This paper extends the results of previous studies on thermalization to modeling of dissipation as energy absorption that takes place during forced vibration of particles in a nonlinear lattice. Results show that dissipation and chaotic behavior of the particles develop simultaneously. Such behavior develops when the forcing frequency falls within a resonance band. The results also support the argument that for a real solid, both in terms of size and complexity, resonance bands overlap significantly broadening the frequency range within which dissipation takes place.

Journal Article↗

PubMed1981

Comparison between the effects of continuous and impact noise on cochlear potentials in guinea pigs.

Cochlear microphonics (CM), action potentials (AP), and endocochlear potential (EP) were recorded from anesthetized, immobilized guinea pigs during potential (EP) were recorded from anesthetized, immobilized guinea pigs during and following 20 min periods of noise exposure. Changes in cochlear potentials were compared in guinea pigs exposed to continuous broadband noise or mechanically generated impact noise of equal energy content. Over a range of continuous noise levels from 95 to 105 dB SPL it was found that continuous noise produced less suppression of CM and a greater suppression of AP than did impact noise of equal energy. A reduction of EP did not accompany CM suppression with either type of noise exposure. Suppression of CM and AP was also compared in guinea pigs with chronically implanted round window electrodes. In these preparations, AP was suppressed to a similar extent by impact and continuous noise of equal energy, but CM was suppressed to a significantly greater extent by impact noise. The data from both series of experiments indicate that the suppression of cochlear responses is not predicted by an "equal energy" rule when impact and continuous noise are compared.

Acoustics↗