Biomedical subjects

H Yurtseven

Publications and source records attributed to H Yurtseven.

13 recordsLinked to original sources

PubMed2006

Specific heat and frequency shifts for the translational modes in ammonia solid I close to phase transition.

The specific heat C(p) is correlated to the frequency shifts (1/nu)( partial differentialnu/ partial differentialT)(p) in ammonia solid I close to the melting point. Our calculated Raman frequencies for the translational modes of nu(T) (100 cm(-1)) and nu(T) (130 cm(-1)), are used for this correlation for the pressures of 0, 1.93 and 3.07 kbar in this crystalline system. We obtain that the specific heat varied linearly with the frequency shifts for those pressures studied and values of the slope dP(m)/dT were extracted. The observed behaviour of the ammonia solid I near the melting point is explained on the basis of our spectroscopic modification of the first Pippard relation.

Ammonia↗

PubMed2006

Temperature and pressure dependence of the mode Grüneisen parameters close to the melting point in hexagonal ice.

We reexamine the Pippard relations in this study by relating the specific heat CP to the Raman frequency shifts 1/nu (partial differentialnu/partial differentialT) P and the thermal expansivity alphap to the 1/nu (partial differentialnu/partial differentialP) T, when the mode Grüneisen parameter depends on the temperature and pressure close to the melting point in hexagonal ice. From linear relations between them, the values of the slope dP/dT are deduced in this crystal. Our slope values calculated here do not change significantly compared to those obtained when the mode Grüneisen parameter is taken as a constant close to the melting point in hexagonal ice.

Crystallography↗

PubMed2006

Temperature dependence of the damping constant and the order parameter close to the lambda phase transitions in ammonium halides.

This study gives our calculation for the damping constant, using the expressions derived for an Ising pseudospin-phonon coupled system in the ammonium halides (NH(4)Cl and NH(4)Br). For this calculation of the damping constant, we use the temperature dependence of the order parameter calculated from the molecular field theory. We predict here the damping constants for the v(5) (174 cm(-1)) and v(5) (177 cm(-1)) Raman modes of NH(4)Cl and NH(4)Br, respectively, below T(lambda) and compare them with our observed bandwidths measured as a function of temperature for those phonon modes at zero pressure. Our predictions agree well with the observed bandwidths below T(lambda) for those modes in both ammonium halide structures, in particular for NH(4)Br. Some discrepancy that occurs below T(lambda) for the v(5) (174 cm(-1)) mode of NH(4)Cl, is explained in terms of the model studied here.

Algorithms↗

PubMed2006

Temperature and pressure dependence of the Raman frequency shifts near the melting point in ice I.

This study examines the validity of the spectroscopic modification of the Pippard relations for the hexagonal ice (ice I) close to the melting point. A linear variation of the specific heat CP with the frequency shifts EQUATION: SEE TEXT is obtained for ice I. This linearity is also obtained between thermal expansivity alphaP and the frequency shifts EQUATION: SEE TEXT close to the melting point in this crystal.

Ice↗

PubMed2005

Raman frequency shifts for the rotatory lattice mode close to the melting point in ammonia solid I.

We correlate here the thermal expansivity alphap to the frequency shifts 1/nu(partial differential nu/partial differential P)T for the rotatory lattice (librational) mode in ammonia solid I close to the melting point. This is carried out for the pressures of 0, 1.93, and 3.07 kbar at various temperatures for this solid structure. By obtaining linear plots of alphap versus 1/nu(partial differential nu/partial differential P)T for the pressures studied, we extract the values of the slope dPm/dT according to our spectroscopic relation. Our calculated values of dPm/dT can be compared with the experimental ones for ammonia solid I close to the melting point.

Journal Article↗

PubMed2005

Bandwidths studied as a function of temperature in ammonium halides near Tlambda.

This study gives our analysis of the Raman bandwidths using the soft mode-hard mode coupling model applied to ammonium halides. The temperature dependence of our observed bandwidths for the nu5(174 cm-1) Raman mode of NH4Cl and nu5(177 cm-1) Raman mode of NH4Br, is analyzed close to phase transitions. From our analysis, we obtain beta=0.13 as the values of the critical exponent for the order parameter in the first order phase region for the ammonium halides.

Ammonium Chloride↗

PubMed2005

Raman frequency shifts of an internal mode near the tricritical and second order phase transitions in NH4Cl.

This study gives our analysis for the frequency shifts of the v2 (1708 cm-1) Raman mode in NH4Cl close to its tricritical (P=1.6 kbar) and second order (P=2.8 kbar) phase transitions. From our analysis, we extract the values of the critical exponent which describes the critical behavior of the Raman frequency shifts for this internal mode for the pressure conditions studied in NH4Cl. Our exponent value of alpha approximately 0.2 for the tricritical phase transition is close to the values of 1/16 (T Tc) for the specific heat, predicted from a 3D Ising model. Our exponent values for the second order phase transition (P=2.8 kbar) for T Tc are comparable with those reported in earlier studies.

Ammonium Chloride↗

PubMed2004

Spectroscopic modification of the Pippard relation applied for the translational mode in ammonia solid II near the melting point.

This study gives our calculation for the frequency shifts 1v partial differentialv partial differentialT(P) and the specific heat C(P) near the melting point in the ammonia solid II. We establish a linear relationship between C(P) and 1v partial differentialv partial differentialT(P) using the Raman frequencies of the translational mode which we calculated in this system. This leads to the validity of the spectroscopic modification of the first Pippard relation in the ammonia solid II near the melting point. From this linear variation of C(P) with the 1v partial differentialv partial differentialT(P) we deduce the slope values of dP(m)dT near the melting point for the fixed pressures of 3.65, 5.02 and 6.57 kbar in the ammonia solid II. They are compared with the experimental dP(m)dT values for this system.

Ammonia↗

PubMed2003

Calculation of the Raman frequencies of the translational mode in ammonia solid II.

We report here our calculated Raman frequencies of the translational mode as a function of temperature for the fixed pressures of 3.65, 5.02 and 6.57 kbars in the ammonia solid II. They were calculated by means of our Grüneisen relation using the volume data from the literature for all the pressures indicated within the temperature regions close to the melting point in this system. Our calculated frequencies are in very good agreement with those observed experimentally for this translational mode of the ammonia solid II. This shows that the observed behaviour of ammonia solid II can be described adequately by means of the calculation employed here.

Ammonia↗

PubMed2002

Calculation of the brillouin frequencies close to phase transitions in NaNO2.

We calculate here the Brillouin frequencies of the L-mode [010], [001] and [100] of NaNO2 for the phase transitions from the paraelectric phase to the sinusoidal anti-ferroelectric phase near the Neel temperature (TN = 437.7 K) and to the ferroelectric phase near the critical temperature (TC = 436.3 K) in this crystalline system. For calculating the frequencies. we use the thermal expansivity data for the phase regions considered, under the assumption that the mode Gruneisen parameter determined for each mode remains constant across the phase transitions. Our calculated frequencies agree well with the observed frequencies for the modes studied in NaNO2.

Kinetics↗

PubMed2002

Spectroscopic modifications of the Pippard relations for NaNO2 in the sinusoidal antiferroelectric phase.

We establish in this study a linear variation of the specific heat Cp with the frequency shifts (l/v)(delta v/delta T) in the sinusoidal antiferroelectric phase of NaNO2, according to the first Pippard relation which we have modified spectroscopically. For this linear relationship we use the Brillouin frequencies of acoustic phonon modes for the q[010], q[001] and q[100] modes of NaNO2 in the sinusoidal antiferroelectric phase. We then calculate dT/dP values due to those modes studied for NaNO2, which agree with the literature values.

Acoustics↗

PubMed2002

Critical behavior of the disorder-induced Raman modes close to the lambda-phase transition in NH4Cl.

This study gives our analysis of the disorder-induced Raman modes of v7 (93 cm(-1)) and v5 (144 cm(-1)) close to the lambda-phase transition (P = 0) in the NH4Cl crystal. We describe the critical behavior of the frequency shifts for those modes by a power-law formula and using our Raman data we obtain the value of 0.1 for the critical exponent which can also describe the critical behavior of the thermal expansivity and the specific heat of NH4Cl close to its lambda-phase transition (Tlambda = 242.9 K).

Ammonium Chloride↗

PubMed2001

Ultrasonic frequencies calculated for the q[100] mode in the first-order, tricritical and the second-order phase transitions of NH4Cl.

This study correlates the volume changes to the ultrasonic frequencies of the q[100] mode of NH4Cl for the first-order, tricritical and the second-order phase transitions in this crystal. Using these correlations we were able to calculate the ultrasonic frequencies of this mode at the pressures of 0, 0.6 and 1.1 kbar (first-order), 1.6 kbar (tricritical) and 2.15 kbar (second-order) by means of the volume change data from the literature. Our calculated frequencies are in good agreement with the observed data for the phase region below the critical temperature T(C) for the first-order, tricritical and the second-order phase transitions in NH4Cl. Above T(C) our calculated frequencies do not agree satisfactorily for the q[100] mode and it is incapable of explaining the observed behaviour of NH4Cl. Our method of calculating the ultrasonic frequencies is presented.

Ammonium Chloride↗