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L Tamam

Publications and source records attributed to L Tamam.

10 recordsLinked to original sources
PubMed2006

Surface freezing in binary alkane-alcohol mixtures.

Surface freezing was detected and studied in mixtures of alcohol and alkane molecules, using surface tensiometry and surface-specific x-ray scattering methods. Considering that surface freezing in pure alkanes forms an ordered monolayer and in alcohols it forms an ordered bilayer, the length mismatch repulsion was minimized by varying the carbon number of the alkane component around 2n, where n is the carbon number of the alcohol molecule. A solutionlike behavior was found for all mixtures, where the ideal liquid mixture phase-separates upon freezing both in the bulk and the surface. The solid exhibits a herringbone crystalline phase below an alkane mole fraction phi(t) approximately 0.8 and a rotator phase above it. The surface frozen film below phi(t) is an alkane monolayer exhibiting a next-nearest neighbor molecular tilt of a composition-dependent magnitude. Above phi(t), no diffraction peaks were observed. This could be explained by the intrinsically shorter-range order of the rotator phase and a possible proliferation of defects.

Journal Article↗
PubMed2005

Crystalline phases of alkyl-thiol monolayers on liquid mercury.

The structure of octadecanethiol monolyers on liquid Hg surfaces, measured with subangstrom resolution, evolves with increasing coverage from a laterally disordered phase of surface-parallel molecules to ordered rotator phases of surface-normal molecules. For the latter, an abrupt transition is found at 19 A(2)/molecule from a rectangular packing of molecules tilted by 27 degrees in the nearest-neighbor direction to a hexagonal unit cell of untilted molecules. The unit cell of the tilted phase is centered for the chains and noncentered for the headgroups. The thiol headgroups associate in pairs with a single Hg atom, and the bonds form long-range orientational order. The different order of thiols on Au(111) and on Hg highlights the subphase's role in determining the overlayer's structure.

Journal Article↗
PubMed2004

Temperature dependence of the structure of Langmuir films of normal-alkanes on liquid mercury.

The temperature dependent phase behavior of Langmuir films of n-alkanes [CH3(CH2)(n-2)CH3, denote Cn] on mercury was studied for chain lengths 19< or =n< or =22 and temperatures 15< or =T< or =44 degrees C, using surface tensiometry and surface x-ray diffraction methods. In contrast with Langmuir films on water, where molecules invariably orient roughly surface normal, alkanes on mercury are always oriented surface parallel and show no long-range in-plane order at any surface pressure. A gas and several condensed phases of single, double, and triple layers of lying-down molecules are found, depending on n and T. At high coverages, the alkanes studied here show transitions from a triple to a double to a single layer with increasing temperature. The transition temperature from a double to a single layer is found to be approximately 5 degrees C, lower than the bulk rotator-to-liquid melting temperature, while the transition from a triple to a double layer is about as much below the double-to-single layer transition. Both monolayer and bulk transition temperatures show a linear increase with n with identical slopes of approximately 4.5 degrees C/CH2 within the range of n values addressed here. It is suggested that the film and bulk transitions are both driven by a common cause: the proliferation of gauche defects in the chain with increasing temperature.

Alkanes↗
PubMed2004

The structure and phase diagram of Langmuir films of alcohols on mercury.

The coverage-dependent phase behavior of molecular films of alcohols (CH3(CH2)n-2CH2OH, denoted as CnOH) on mercury was studied for chain lengths 8 < or = n < or = 28, using surface tensiometry and surface specific X-ray methods. Phases with surface-normal-oriented molecules are found at high coverage, showing the CS, S, and LS phases found also on water. Phases comprising surface parallel molecules, which do not exist on water, are found here at low coverage. For the lowest coverage a two-dimensional gas phase is found, followed, upon increasing the coverage, by an n-dependent sequence of condensed phases of up to four layers of surface-parallel molecules before converting to the surface-normal phases. In contrast with the surface-normal phases, all of the surface-parallel phases are found to lack long-range order in the surface-parallel direction. Adsorption energies are derived from the phase diagram for the alkyl chain and the alcohol headgroup.

Adsorption↗
PubMed2004

Fatty acid Langmuir films on liquid mercury: X-ray and surface tension studies.

The structure and phase behavior of liquid-mercury-supported molecular films of fatty acids (CH3(CH2)n-2COOH, denoted CnOOH) were studied for molecular lengths 7 < or = n < or = 24, by surface tensiometry and X-ray methods. Two qualitatively different film structures were found, depending on coverage. For high coverage, the film consists of a monolayer of roughly surface-normal molecules, showing a pressure-dependent sequence of structures similar, though not identical, to that of the corresponding water-supported Langmuir films. At low coverage, phases consisting of surface-parallel molecules are found, not observed on the aqueous subphases employed to date. In this range, a two-dimensional (2D) gas followed by a single and, for 14 < or = n < or = 24, also by a double layer of surface-parallel molecules is found as coverage is increased. Depending on chain length, the flat-lying phases have a crystalline 2D-ordered, a smectic-like 1D-ordered, or a disordered in-plane structure consisting of molecular dimers. The structure and thermodynamics of the films are discussed.

Fatty Acids↗
PubMed2001

Suicide during clozapine treatment: a case report.

The risk of suicide among patients with schizophrenia is greater than that in the general population. Although clozapine, along with its other significant features, has been reported to decrease suicidality and suicide rate among schizophrenia patients, physicians should remain vigilant for general risk factors of suicide in patients with schizophrenia during a treatment course and assess them carefully. Awareness of the effect of the illness, a sense of inadequacy to achieve goals, a change in the course of the illness, an improvement after relapse and a proposed discharge from the hospital in the near future are factors that should be noted especially within these general risk factors for suicide. In this case report, we presented a schizophrenia patient with several risk factors who committed suicide during clozapine treatment. Risk factors prominent in this case including increased awareness after improvement in chronic state, planned discharge in the near future, and the notion of reduced suicidality in schizophrenia patients during clozapine treatment are discussed in this article based on the literature and the case.

Adult↗
PubMed2000

Association between idiopathic mitral valve prolapse and panic disorder.

AIM: To evaluate the association between idiopathic mitral valve prolapse and panic disorder. METHODS: The study comprised 50 patients with idiopathic mitral valve prolapse, 50 patients with panic disorder, and 50 healthy controls. All subjects underwent echocardiographic evaluation. If idiopathic mitral valve prolapse was present, the level of prolapse was measured. To reach psychiatric diagnosis, the Structured Clinical Interview for DSM-IV Axis I Disorders, clinician version, was administered to all subjects. For psychometric evaluation, all subjects completed the Symptom Check List, Beck Depression Inventory, and State and Trait Anxiety Inventory. RESULTS: The prevalence of panic disorder was 16% in patients with idiopathic mitral valve prolapse, and 2% in healthy controls (p=0.03). The average scores on all psychometric scales were the highest in the panic disorder group, whereas average scores in idiopathic mitral valve prolapse group were significantly higher than in the control group (p<0.001). Idiopathic mitral valve prolapse and panic disorder groups displayed similar features of panic attack symptoms. Panic disorder cases with idiopathic mitral valve prolapse and those without it did not significantly differ in terms of psychometric evaluations and clinical symptoms. CONCLUSION: The possibility of comorbidity of panic disorder and idiopathic mitral valve prolapse should be taken into account in the approach to the patients diagnosed with either of the disorders.

Adolescent↗