Quantum-Mechanical Relation between Atomic Dipole Polarizability and the van der Waals Radius

The atomic dipole polarizability α and the van der Waals (vdW) radius R_{vdW} are two key quantities to describe vdW interactions between atoms in molecules and materials. Until now, they have been determined independently and separately from each other. Here, we derive the quantum-mechanical relation R_{vdW}=const×α^{1/7}, which is markedly different from the common assumption R_{vdW}∝α^{1/3} based on a classical picture of hard-sphere atoms. As shown for 72 chemical elements between hydrogen and uranium, the obtained formula can be used as a unified definition of the vdW radius solely in terms of the atomic polarizability. For vdW-bonded heteronuclear dimers consisting of atoms A and B, the combination rule α=(α_{A}+α_{B})/2 provides a remarkably accurate way to calculate their equilibrium interatomic distance. The revealed scaling law allows us to reduce the empiricism and improve the accuracy of interatomic vdW potentials, at the same time suggesting the existence of a nontrivial relation between length and volume in quantum systems.

Minoxidil analysis in human plasma using high-performance liquid chromatography with electrochemical detection. Application to pharmacokinetic studies

A method is described for determination of minoxidil in human plasma using high-performance liquid chromatography with electrochemical detection. The method is specific and sensitive (500 pg/ml), however, minoxidil and minoxidil sulfate cannot be differentiated due to rapid autohydrolysis of minoxidil sulfate to minoxidil. The extraction procedure employs a C18 preparatory column to remove endogenous plasma constituents which would interfere with the assays. The calibration curves are linear for concentrations from 500 pg to 10 ng/ml. Within-day and between-day reproducibility are satisfactory with coefficient of variation less than 5.7% for all concentrations. Sample recovery from extraction is consistent at 45 to 55% at low and high concentrations, respectively. A pharmacokinetic study in a hypertensive volunteer receiving two different oral doses of minoxidil (1.25 and 2.5 mg) on different occasions demonstrates the utility of the method.

Coulomb interactions between dipolar quantum fluctuations in van der Waals bound molecules and materials

Mutual Coulomb interactions between electrons lead to a plethora of interesting physical and chemical effects, especially if those interactions involve many fluctuating electrons over large spatial scales. Here, we identify and study in detail the Coulomb interaction between dipolar quantum fluctuations in the context of van der Waals complexes and materials. Up to now, the interaction arising from the modification of the electron density due to quantum van der Waals interactions was considered to be vanishingly small. We demonstrate that in supramolecular systems and for molecules embedded in nanostructures, such contributions can amount to up to 6 kJ/mol and can even lead to qualitative changes in the long-range van der Waals interaction. Taking into account these broad implications, we advocate for the systematic assessment of so-called Dipole-Correlated Coulomb Singles in large molecular systems and discuss their relevance for explaining several recent puzzling experimental observations of collective behavior in nanostructured materials.

Long-Range Repulsion Between Spatially Confined van der Waals Dimers

It is an undisputed textbook fact that nonretarded van der Waals (vdW) interactions between isotropic dimers are attractive, regardless of the polarizability of the interacting systems or spatial dimensionality. The universality of vdW attraction is attributed to the dipolar coupling between fluctuating electron charge densities. Here, we demonstrate that the long-range interaction between spatially confined vdW dimers becomes repulsive when accounting for the full Coulomb interaction between charge fluctuations. Our analytic results are obtained by using the Coulomb potential as a perturbation over dipole-correlated states for two quantum harmonic oscillators embedded in spaces with reduced dimensionality; however, the long-range repulsion is expected to be a general phenomenon for spatially confined quantum systems. We suggest optical experiments to test our predictions, analyze their relevance in the context of intermolecular interactions in nanoscale environments, and rationalize the recent observation of anomalously strong screening of the lateral vdW interactions between aromatic hydrocarbons adsorbed on metal surfaces.

The effect of hysterectomy on urinary symptoms and residual bladder volume

This was a prospective, clinical study to evaluate the effect of abdominal and vaginal hysterectomy for benign indications on urinary symptoms and residual bladder volume. One hundred and seven women undergoing hysterectomy for benign conditions were included in the study that took place in a district general hospital between April 1998 and January 2000. Urinary symptoms such as stress incontinence of urine, urgency, frequency, nocturia, sensation of incomplete voiding and voiding difficulties were considered. A questionnaire was filled out and the residual bladder volume measured with a 'Bard' bladder scanner on three occasions-before the operation, postoperative days 3 or 4 and at the 6-week postoperative visit. Statistical analysis involved using a generalised estimating equation and significance assessed at the 5% level. Each woman acted as her own control. There was no evidence of changes in nocturia and voiding difficulties after surgery. All other symptoms and residual bladder volumes decreased significantly postoperatively. The type of hysterectomy did not have an effect.

Vaginal sacrospinous fixation: experience in a district general hospital

This is an observational retrospective study, which included 77 patients who underwent sacrospinous fixation (SSF) over a period of 3 years in a district general hospital. Casenotes were reviewed and all patients were invited to attend a further review appointment (14-49 months). The object was to determine short- and long-term success of SSF,particularly in elderly (28% were > or = 70 years), obese (24.7%) and medically compromised (64.9%) patients. Fifty-two patients (67.5%) had previous gynaecological procedures, while the remaining 25 (32.5%) had no previous surgery. Intra- and postoperative complications were 3.9% and 32.5%, respectively. There was considerable relief of patients' symptoms at both short- and long-term followup, while the rate of recurrence of vault prolapse was 10.3%. Our experience suggests that SSF appears to be a safe and effective procedure, especially for those who may constitute surgical or anaesthetic risks. It has a reasonable success rate, good postoperative recovery and acceptable long-term results.

Otitis media with effusion in children and its correlation with foreign body in the external auditory canal

Otitis Media with Effusion (OME) is difined as the chronic accumulation of mucus within the middle ear and sometimes the mastoid air cell system. Significant hearing loss may go unnoticed and may result in improper development of speech and language. Foreign bodies in the external auditory canal of paediatric patients are commonly encountered in day-to-day practice. The purpose was to see if there is any relation between foreign bodies in ears and otitis media with effusion. A prospective study of consecutive cases was conducted between August 2005 and August 2007 at a teaching hospital. All children presenting with the history of a foreign body in the external auditory canal were included in this study. 50/74 that is 67.8% of the children in the study group had abnormal findings in the tympanogram whereas only 28/74 that is 37.8% children from the control group had abnormal findings in tympanogram. This study indicates that significant eustachian tube dysfunction to frank OME, causes irritation and/or earache in children which may compel them to put things into the ear. So children with an external auditory foreign body must be followed up in an ENT clinic. This may be an early opportunity to diagnose an underlying undetected OME and/or eustachian tube dysfunction in children, preventing the development of any complication from the undetected OME.

Modeling coarse-grained van der Waals interactions using dipole-coupled anisotropic quantum Drude oscillators

The Quantum Drude Oscillator (QDO) model is a promising candidate for accurately calculating the van der Waals (vdW) interaction. Anisotropic QDO models have recently been used to represent quantum fluctuations of molecular fragments rather than that of single atoms. While this model promises accurate calculation of vdW energy, there is significant room for improvements, such as incorporating a proper fragmentation method, higher-order dispersion corrections, and so forth. The present work attempts to gauge dipole-dipole interactions' ability without fragmentation. A suitable anisotropic damping function is also introduced to work with anisotropic QDO. This revised model accurately predicts the binding energies of vdW complexes for most of the systems considered. This work indicates the limit of dipole approximation for an anisotropic QDO-based model.

An investigation into possible quantum chaos in the H2 molecule under intense laser fields via Ehrenfest phase space (EPS) trajectories

By employing the Ehrenfest "phase space" trajectory method for studying quantum chaos, developed in our laboratory, the present study reveals that the H₂ molecule under intense laser fields of three different intensities, I = 1 × 10¹⁴ W/cm², 5 × 10¹⁴ W/cm², and 1 × 10¹⁵ W/cm², does not show quantum chaos. A similar conclusion is also reached through the Loschmidt echo (also called quantum fidelity) calculations reported here for the first time for a real molecule under intense laser fields. Thus, a long-standing conjecture about the possible existence of quantum chaos in atoms and molecules under intense laser fields has finally been tested and not found to be valid in the present case.

A simple fragment-based method for van der Waals corrections over density functional theory

Modeling intermolecular noncovalent interactions between large molecules remains a challenge for the electron structure theory community due to the high cost. Fragment-based methods usually fare well in reducing the cost...