Caldeira-Leggett model vs ab initio potential: A vibrational spectroscopy test of water solvation.

We present a semiclassically approximate quantum treatment of solvation with the purpose of investigating the accuracy of the Caldeira-Leggett model. We do that by simulating the vibrational features of water solvation by means of two different approaches. One is entirely based on the adoption of an accurate ab initio potential to describe water clusters of increasing dimensionality. The other one consists of a model made of a central water molecule coupled to a high-dimensional Caldeira-Leggett harmonic bath. We demonstrate the role of quantum effects in the detection of water solvation and show that the computationally cheap approach based on the Caldeira-Leggett bath is only partially effective. The main conclusion of the study is that quantum methods associated with high-level potential energy surfaces are necessary to correctly study solvation features, while simplified models, even if attractive owing to their reduced computational cost, can provide some useful insights but are not able to come up with a comprehensive description of the solvation phenomenon.

Machine learning for vibrational spectroscopy via divide-and-conquer semiclassical initial value representation molecular dynamics with application to N-methylacetamide.

A machine learning algorithm for partitioning the nuclear vibrational space into subspaces is introduced. The subdivision criterion is based on Liouville's theorem, i.e., the best preservation of the unitary of the reduced dimensionality Jacobian determinant within each subspace along a probe full-dimensional classical trajectory. The algorithm is based on the idea of evolutionary selection, and it is implemented through a probability graph representation of the vibrational space partitioning. We interface this customized version of genetic algorithms with our divide-and-conquer semiclassical initial value representation method for the calculation of molecular power spectra. First, we benchmark the algorithm by calculating the vibrational power spectra of two model systems, for which the exact subspace division is known. Then, we apply it to the calculation of the power spectrum of methane. Exact calculations and full-dimensional semiclassical spectra of this small molecule are available and provide an additional test of the accuracy of the new approach. Finally, the algorithm is applied to the divide-and-conquer semiclassical calculation of the power spectrum of 12-atom trans-N-methylacetamide.

How many water molecules are needed to solvate one?

Many efforts undertaken to study the solvation process have led to general theories that may describe mean properties, but are unable to provide a detailed understanding at the molecular level. Remarkably, the basic question of how many solvent molecules are necessary to solvate one solute molecule is still open. By exploring several water aggregates of increasing complexity, in this contribution we employ semiclassical spectroscopy to determine on quantum dynamical grounds the minimal network of surrounding water molecules to make the central one display the same vibrational features of liquid water. We find out that double-acceptor double-donor tetrahedral coordination constituting the standard picture is necessary but not sufficient, and that particular care must be reserved for the quantum description of the combination band due to the coupling of the central monomer bending mode with network librations. It is actually our ability to investigate the combination band with a quantum-derived approach that allows us to answer the titular question. The minimal structure eventually responsible for proper solvation is made of a total of 21 water molecules and includes two complete solvation shells, of which the whole first one is tetrahedrally coordinated to the central molecule.

Improved semiclassical dynamics through adiabatic switching trajectory sampling.

We introduce an improved semiclassical dynamics approach to quantum vibrational spectroscopy. In this method, a harmonic-based phase space sampling is preliminarily driven toward non-harmonic quantization by slowly switching on the actual potential. The new coordinates and momenta serve as initial conditions for the semiclassical dynamics calculation, leading to a substantial decrease in the number of chaotic trajectories to deal with. Applications are presented for model and molecular systems of increasing dimensionality characterized by moderate or high chaoticity. They include a bidimensional Henon-Heiles potential, water, formaldehyde, and methane. The method improves accuracy and precision of semiclassical results and it can be easily interfaced with all pre-existing semiclassical theories.

Pediatrician knowledge and attitudes regarding human papillomavirus disease and its prevention.

Between 1 September and 8 October 2006, we used a self-administered, anonymous questionnaire in order to evaluate knowledge and attitudes regarding HPV disease and its prevention in a nationally representative sample of Italian pediatricians. Three hundred and eleven of the 400 enrolled physicians (175 primary care pediatricians, 160 hospital pediatricians and 65 residents in pediatrics) returned completed surveys (227 females; mean age+/-standard deviation, 45.3+/-11.61 years). The results showed a lack of knowledge concerning HPV disease and its prevention, with marginal differences between the subgroups, even though the majority would recommend HPV vaccination. These findings highlight an urgent need to improve pediatrician information in order to ensure the optimal implementation of HPV vaccination, and the adequate acceptability of HPV vaccines to adolescents and their parents.

Impact on respiratory tract infections of heptavalent pneumococcal conjugate vaccine administered at 3, 5 and 11 months of age.

BACKGROUND: Medical and public health importance of pneumococcal infections justifies the implementation of measures capable of reducing their incidence and severity, and explains why the recently marketed heptavalent pneumococcal conjugate vaccine (PCV-7) has been widely studied by pediatricians. This study was designed to evaluate the impact of PCV-7 administered at 3, 5 and 11 months of age on respiratory tract infections in very young children. METHODS: A total of 1,571 healthy infants (910 males) aged 75-105 days (median 82 days) were enrolled in this prospective cohort trial to receive a hexavalent vaccine (DTaP/IPV/HBV/Hib) and PCV-7 (n = 819) or the hexavalent vaccine alone (n = 752) at 3, 5 and 11 months of age. Morbidity was recorded for the 24 months following the second dose by monthly telephone interviews conducted by investigators blinded to the study treatment assignment using standardised questionnaires. During these interviews, the caregivers and the children's pediatricians were questioned about illnesses and the use of antibiotics since the previous telephone call. All of the data were analysed using SAS Windows v.12. RESULTS: Among the 1,555 subjects (98.9%) who completed the study, analysis of the data by the periods of follow-up demonstrated that radiologically confirmed community-acquired pneumonia (CAP) was significantly less frequent in the PCV-7 group during the follow-up as a whole and during the last period of follow-up. Moreover, there were statistically significant between-group differences in the incidence of acute otitis media (AOM) in each half-year period of follow-up except the first, with significantly lower number of episodes in children receiving PCV-7 than in controls. Furthermore, the antibiotic prescription data showed that the probability of receiving an antibiotic course was significantly lower in the PCV-7 group than in the control group. CONCLUSION: Our findings show the effectiveness of the simplified PCV-7 schedule (three doses administered at 3, 5 and 11-12 months of age) in the prevention of CAP and AOM, diseases in which Streptococcus pneumoniae plays a major etiological role. A further benefit is that the use of PCV-7 reduces the number of antibiotic prescriptions. All of these advantages may also be important from an economic point of view.

Impact of human coronavirus infections in otherwise healthy children who attended an emergency department.

This prospective clinical and virological study of 2,060 otherwise healthy children aged <15 years of age (1,112 males; mean age +/- SD, 3.46 +/- 3.30 years) who attended the Emergency Department of Milan University's Institute of Pediatrics because of an acute disease excluding trauma during the winter season 2003-2004 was designed to compare the prevalence and clinical importance of human coronaviruses (HCoVs) in children. Real-time polymerase chain reaction (PCR) in nasopharyngeal aspirates revealed HCoV infection in 79 cases (3.8%): 33 HCoV-229E (1.6%), 13 HCoV-NL63 (0.6%), 11 HCoV-OC43 (0.5%), none HCoV-HKU1 genotype A, and 22 (1.1%) co-detections of a HCoV and another respiratory virus. The HCoVs were identified mainly in children with upper respiratory tract infection; there was no significant difference in clinical presentation between single HCoV infections and HCoV co-infections. Diagnostic methods were used in a limited number of patients, and the therapy prescribed and clinical outcomes were similar regardless of the viral strain. There were a few cases of other members of the households of HCoV-positive children falling ill during the 5-7 days following enrollment. These findings suggest that HCoV-229E and HCoV-OC43 have a limited clinical and socioeconomic impact on otherwise healthy children and their household contacts, and the HCoV-NL63 identified recently does not seem to be any different. The quantitative and qualitative role of HCoV-HKU1 genotype A is apparently very marginal.

Differences in nasopharyngeal bacterial flora in children with nonsevere recurrent acute otitis media and chronic otitis media with effusion: implications for management.

BACKGROUND: The interactions between nasopharyngeal flora and the individual entities covered by the broad term otitis media have not been completely elucidated. We investigated in infants and children ages 6 months to 7 years with nonsevere recurrent acute otitis media (rAOM) or with chronic otitis media with effusion (cOME): (1) the nasopharyngeal carriage rate and bacterial density of respiratory pathogens and alpha-hemolytic streptococci in comparison with healthy children; (2) the resistance pattern of respiratory pathogens; and (3) the relationship between the type of nasopharyngeal colonization and long term outcome. METHODS: Nasopharyngeal cultures were obtained from 85 children with rAOM,113 children with cOME and 55 controls. A semiquantitative analysis was used in the reading of cultures. A 12-week follow-up without treatment was planned. RESULTS: The carrier rate of respiratory pathogens was significantly greater in cOME (70%) than in rAOM (45%) (P = 0.0006) or controls (31%) (P < 0.0001). Similarly colonization density was significantly greater in cOME than in rAOM. The carriage rate and the colonization density of alpha-hemolytic streptococci were significantly lower in rAOM than in cOME or controls. The incidence of resistant (R) strains was greater in rAOM (Streptococcus pneumoniae penicillin-R, 24%; macrolide-R, 64%; Haemophilus influenzae amoxicillin-R, 24%) compared with cOME (S. pneumoniae penicillin-R,18%; macrolide-R, 44%; H. influenzae amoxicillin-R, 5%) or controls (S. pneumoniae penicillin-R, 8%; macrolide-R, 23%; H. influenzae amoxicillin-R, 10%). During the follow-up period persistence of OME and occurrence of AOM were greater among carriers of respiratory pathogens at baseline. CONCLUSIONS: There are substantial differences in nasopharyngeal flora between children with nonsevere rAOM and children with cOME. The results of nasopharyngeal cultures should be taken into account to avoid treatment with drugs that are ineffective and likely to select resistant organisms.