Origin-Independent Dynamic Polarizability Density from Coupled Cluster Response Theory.

The calculation of the origin-independent density of the dynamic electric dipole polarizability, previously presented for uncorrelated and density functional theory (DFT)-based methods, has been developed and implemented at the coupled cluster singles and doubles (CCSD) level of theory. A pointwise analysis of polarizability densities calculated for a number of molecules at Hartree-Fock (HF) and CCSD clearly shows that the electron correlation effect is much larger than one would argue considering the integrated dipole electric polarizability alone. Large error compensations occur during the integration process, which hide fairly large deviations mainly located in the internuclear regions. The same is observed when calculated CCSD and B3LYP polarizability densities are compared, with the remarkable feature that positive/negative deviations between CCSD and HF reverse sign, becoming negative/positive when comparing CCSD to B3LYP.

On the topology of total and diamagnetic induced electronic currents in molecules.

An application of the continuous transformation of the origin of the current density (CTOCD) scheme to constrain the diamagnetic induced charge current density (Jd) to be divergenceless is introduced. This results in a family of Jd fields perpendicular and proportional to both the gradient of the electron density and the external magnetic field. Since, in the limit of a complete basis set calculation, the paramagnetic component Jp also becomes divergenceless, we call this scheme CTOCD-DC (CTOCD for Divergenceless Components). CTOCD-DC allows for a topological characterization of both Jd and Jp in terms of their stagnation graphs. All stagnation graphs of Jd from CTOCD-DC contain the zero points of the gradient of the unperturbed electron density (∇ρ). In this way, an intimate topological relation between ρ and the diamagnetic current contribution is revealed. Numerical experiments exemplified by the case of LiNHF in point group symmetry C1 suggest that the corresponding paramagnetic current contributions Jp can show tendencies to accumulate pseudo-stagnation lines in proximity of some kind of the zero points of ∇ρ. Common zero points of ∇ρ and the total currents are exactly zero points of the mechanical momentum density.

A Novel Cooling Device for Targeted Brain Temperature Control and Therapeutic Hypothermia: Feasibility Study in an Animal Model.

BACKGROUND: Therapeutic hypothermia (i.e., temperature management) is an effective option for improving survival and neurological outcome after cardiac arrest and is potentially useful for the care of the critically ill neurological patient. We analyzed the feasibility of a device to control the temperature of the brain by controlling the temperature of the blood flowing through the neck. METHODS: A lumped parameter dynamic model, with one-dimensional heat transfer, was used to predict cooling effects and to test experimental hypotheses. The cooling system consisted of a flexible collar and was tested on 4 adult sheep, in which brain and body temperatures were invasively monitored for the duration of the experiment. RESULTS: Model-based simulations predicted a lowering of the temperature of the brain and the body following the onset of cooling, with a rate of 0.4 °C/h for the brain and 0.2 °C/h for the body. The experimental findings showed comparable cooling rates in the two body compartments, with temperature reductions of 0.6 (0.2) °C/h for the brain and 0.6 (0.2) °C/h for the body. For a 70 kg adult human subject, we predict a temperature reduction of 0.64 °C/h for the brain and 0.43 °C/h for the body. CONCLUSIONS: This work demonstrates the feasibility of using a non-invasive method to induce brain hypothermia using a portable collar. This device demonstrated an optimal safety profile and represents a potentially useful method for the administration of mild hypothermia and temperature control (i.e., treatment of hyperpyrexia) in cardiac arrest and critically ill neurologic patients.

Chiral discrimination via nuclear magnetic shielding polarisabilities from NMR spectroscopy: theoretical study of (R(a))-1,3-dimethylallene, (2R)-2-methyloxirane, and (2R)-N-methyloxaziridine.

Three medium-size optically active molecules have been studied to make a guess at candidates suitable for chiral discrimination in an isotropic medium via nuclear magnetic resonance spectroscopy. The criterion for experimental detection is given by the magnitude of the isotropic part of nuclear magnetic shielding polarisability tensors, related to a pseudoscalar of opposite sign for the two enantiomers. The pseudoscalar shielding polarisability at the (17)O nucleus in N-methyloxaziridine, calculated at the Hartree-Fock level, is approximately 7.8 x10(-)(17) mV(-)(1). To obtain an experimentally observable magnetic field induced at the (17)O nucleus in N-methyloxaziridine, electric fields as large as approximately 10(7) - 10(8) Vm(-)(1) should be applied to the probe. The molecular electric dipole moment induced by precession of the magnetic dipole of the (17)O nucleus in a magnetic field of 10 T is, in absolute value, approximately 8.8 x 10(-)(42) Cm. The estimated rf-voltage at a resonance circuit is approximately 10 nV. Smaller values have been estimated for N, C, and H nuclei in 1,3-dimethylallene and 2-methyloxirane.

Why downfield proton chemical shifts are not reliable aromaticity indicators.

Traces of magnetizability, traces of magnetic shielding at the hydrogen nuclei, and nucleus-independent chemical shift are not reliable aromaticity quantifiers for planar conjugated hydrocarbons. A measure of aromaticity is provided by the out-of-plane tensor components, whose magnitude is influenced by the pi-ring currents. The failure of nucleus-independent chemical shift in this regard was proved for the molecule shown in the abstract graphic, sustaining a diatropic pi-current. The validity of the ring-current model is reaffirmed. [structure: see text]

Parity-violating effects in asymmetric chemical reactions: A theoretical study on the CHFClBr molecule

A coupled Hartree-Fock procedure has been employed to estimate the parity-violating energy contribution due to electroweak interaction in the vicinity of the transition point of a chemical reaction path starting from achiral reagents and producing the chiral CHFClBr molecule. The calculations demonstrate that (i) the S enantiomer is a reaction product more stable than its mirror image by approximately 1x10(-17) hartree; (ii) in the transition state of the reaction, the chiral activated complex evolving toward the S-CHFClBr species is more stable, by approximately 2.3x10(-17) hartree, than the enantiomeric activated complex that would yield the R-CHFClBr species. These results suggest that kinetic effects at work during chemical syntheses of chiral molecules might be more significant than the different thermodynamical stability of the two mirror-image reaction products in determining the final configuration and to explain homochirality.

Energetic stabilization of d-camphor via weak neutral currents.

It is shown via a series of numerical tests on the camphor molecule, C10H16O, that the naturally occurring d-enantiomer is energetically stabilized with respect to its mirror image by electroweak force. The calculated energy difference between enantiomers, about 1.5 x 10(-19) hartree, is roughly eight orders of magnitude smaller than the upper bound suggested by available spectroscopic investigations on the frequency of a spectroscopic transition. However, such a difference is about ten times larger than previous estimates of parity-violating energy contributions reported in the literature for other chiral molecules, which makes the idea of electroweak stabilization of one enantiomer more reliable than expected before.

Intramedullary osteosynthesis 3. Küntscher nailing in the humerus.

With regard for the principles that govern the correct application of intramedullary osteosynthesis in the long bones of the lower limb, the authors also support its use in the humerus. After an exhaustive survey of the specific problems at this site, a critical review of 130 cases observed over the last 15 years is reported. Extremely favourable results emerged in the treatment of the humerus with this means of synthesis, thanks to its surgical, mechanical and biological advantages.

Intramedullary osteosynthesis. 4. Küntscher nailing in the ulna.

Intramedullary osteosynthesis with Küntscher nailing is an appropriate and extremely effective operation in the treatment of diaphyseal fractures of the ulna. Like the other long bones of the limbs (femur, humerus, tibia), in the ulna, as well, the advantages of the method, particularly when performed in closed surgery, are undeniable, so much so that this bone has a shape which is particularly favourable to nailing. The authors present and discuss their personal series of cases reporting results which are excellent. Thus, once again, the great reliability of this simple means of synthesis, in use for more than 20 years, is emphasised, and the subject is completed with a series of previous technical suggestions on how to obtain the best results.

Intramedullary osteosynthesis. 1. Küntscher nailing in the femur.

Based on more than 20 years experience, the authors support the effectiveness of intramedullary nailing in the treatment of diaphyseal fractures of the femur. They review the history and advantages of this method and discuss the biomechanical principles on which it is based. Recent advances in technique have made it possible to secure proximal and distal anchorage in cancellous bone. This allows the method to be extended to more proximal and distal fractures than in the traditional method which is applicable only to the middle third. It also facilitates progressive axial compression, early loading and early mobilisation of the limb, thus creating the optimum biological conditions for consolidation and joint function. The closed method also reduces blood loss and the risk of infection. The techniques adopted to deal with more complex situations are described. These include moderately comminuted oblique and spiral fractures and certain bifocal fractures. Finally, the results of treating 450 cases are reviewed, with a longterm analysis of 198 patients.

Intramedullary osteosynthesis. 2. Küntscher nailing in fractures of the tibia.

The purpose of this study is to discuss diaphyseal fractures of the tibia treated by intramedullary Küntscher nailing. This is based on 368 cases treated over the last 20 years. Closed intramedullary osteosynthesis favours the healing process, resulting in the early formation of callus which is of good quality and abundant. A careful review of the cases showed a 93.7% incidence of good results.

Long-term results of intersomatic lumbar fusion with a posterior approach.

The authors discuss the advantages of using intersomatic lumbar fusion with a posterior approach for the treatment of low back pain due to discopathy or grade I spondylolisthesis. After a description of the surgical method used, the long-term results obtained in 16 cases are presented. The clinical and radiographic results are good in cases of discopathy, while in those of spondylolisthesis there is disagreement between the clinical evaluation, which is generally satisfactory, and the radiographic evaluation which is not quite as satisfactory.

Alignment of the extensor apparatus of the knee by alar and tuberosity transposition in recurrent subluxation of the patella and in external patellar hypertension syndrome.

In consideration of the multiple anatomical structures involved in recurrent subluxation of the patella and in external patellar hypertension syndrome, the authors propose an operation which allows for complete realignment of the extensor apparatus by transposition of the anterior tibial tuberosity, division of the external alar ligament, tightening of the internal alar ligament, and correction of the muscular insertions. In particular, removal of a capsulofascial band medially and its reimplantation into the external incision is proposed, thus avoiding the formation of retractive scar tissue. The long-term results, which were overall satisfactory, confirm the effectiveness of the operation proposed.

Prevention of deep venous thrombosis in orthopedic surgery: effects of defibrotide.

The effectiveness of defibrotide was compared with that of calcium heparin and acetylsalicylic acid (ASA) in the prevention of deep venous thrombosis (DVT) resulting from orthopedic surgery. Sixty-three patients scheduled for elective or traumatological surgery, for the most part involving the hip joint, were recruited. The patients were randomly assigned to one of the following treatment groups: defibrotide (400 mg twice daily), administered intramuscularly (n = 19); calcium heparin (5,000 IU thrice daily), administered subcutaneously (n = 25); and ASA (100 mg on alternate days), administered orally (n = 19). Administration of the drug was started one day before surgery and continued until the seventh day after surgery. Each patient was monitored daily by means of the fibrinogen uptake test. The incidence of increased uptake did not differ significantly in the three groups (defibrotide, ten out of 19; calcium heparin, ten out of 25; ASA, seven out of 19). Conversely, a trend in favor of defibrotide was noted in cases of symptomatic DVT (defibrotide, one out of 19; calcium heparin, two out of 25; ASA, four out of 19) and pulmonary embolism (defibrotide, no cases; calcium heparin, one case; ASA two cases). On the strength of these findings, defibrotide therapy qualifies as a valid alternative to conventional DVT prophylaxis in orthopedic surgery.

Intramedullary nailing with supplementary screw fixation (Grosse-Kempf technique).

The authors report their experience in 25 cases of fractures of the shaft of the femur and tibia treated by the Grosse-Kempf method of intramedullary nailing supplemented by screw fixation. They confirm the validity of this technique, which enlarges the indications for intramedullary nailing and offers an alternative method of osteosynthesis in the more severe cases.