DFT Investigations of the Vibrational Spectra and Translational Modes of Ice II.

The vibrational spectrum of ice II was investigated using the CASTEP code based on first-principles density functional theory (DFT). Based on good agreement with inelastic neutron scattering (INS), infrared (IR), and Raman experimental data, we discuss the translation, libration, bending, and stretching band using normal modes analysis method. In the translation band, we found that the four-bond and two-bond molecular vibration modes constitute three main peaks in accordance with INS ranging from 117 to 318 cm-1. We also discovered that the lower frequencies are cluster vibrations that may overlap with acoustic phonons. Whale et al. found in ice XV that some intramolecular vibrational modes include many isolated-molecule stretches of only one O-H bond, whereas the other O-H bond does not vibrate. This phenomenon is very common in ice II, and we attribute it to local tetrahedral deformation. The pathway of combining normal mode analysis with experimental spectra leads to scientific assignments.

Computational Analysis of Exotic Molecular and Atomic Vibrations in Ice XV.

It is always difficult to assign the peaks of a vibrational spectrum in the far-infrared region. The two distinct peaks seen in many ice phases are still a mystery to date. The normal modes of ice XV were calculated using the CASTEP code based on first-principles density functional theory. On the basis of vibrational modes analysis, we divided the translational modes into three categories: four-bond vibrations, which have the highest energy levels; two-bond vibrations, which have medium levels of energy; and relative vibrations between two sublattices, which have the lowest energy. Whale et al. found that some intramolecular stretching modes include the isolated vibration of only one O-H bond, whereas the others do not vibrate in ice XV. We verified this phenomenon in this study and attributed it to local tetrahedral deformation. Analysis of normal modes, especially in the translation and stretching band of ice XV, clarified the physical insights of the vibrational spectrum and can be used with other ice phases.

DFT Simulations of the Vibrational Spectrum and Hydrogen Bonds of Ice XIV.

It is always a difficult task to assign the peaks recorded from a vibrational spectrum. Herein, we explored a new pathway of density functional theory (DFT) simulation to present three kinds of spectra of ice XIV that can be referenced as inelastic neutron scattering (INS), infrared (IR), and Raman experimental spectrum. The INS spectrum is proportional to the phonon density of states (PDOS) while the photon scattering signals reflect the normal vibration frequencies near the Brillouin zone (BZ) center. Based on good agreements with the experimental data, we identified the relative frequency and made scientific assignments through normal vibration modes analysis. The two hydrogen bond (H-bond) peaks among the ice phases from INS were discussed and the dynamic process of the H-bond vibrations was found to be classified into two basic modes. We deduced that two H-bond modes are a general rule among the ice family and more studies are ongoing to investigate this subject.

Exotic Spectra and Lattice Vibrations of Ice X Using the DFT Method.

A typical vibrational spectrum in the ice phase has four separate bands: Translation, libration, bending, and stretching. Ice X, the final ice phase under high pressure, shows an exotic vibrational spectrum. Based on harmonic approximation, an ideal crystal of ice X has one peak, at 998 cm-1, for Raman scattering and two peaks, at 450 cm-1 and 1507 cm-1, for infrared absorption in this work. These three characteristic peaks are indicators of the phase transition between ice VII and VIII and ice X. Despite many experimental and theoretical works on ice X, only this study has clearly indicated these characteristic peaks in the region of the IR band. The phonon density of states shows quite different features than ice VIII, which could be verified by inelastic neutron scattering in the future. The dynamic processes of 15 vibrational normal modes are discussed and the typical hydrogen bonds are missing.

Comparative Analysis of the Hydrogen Bond Vibrations of Ice XII.

It is difficult to theoretically study the vibrational spectrum of hydrogen-disordered ice XII compared with its hydrogen-ordered counterpart, ice XIV. We constructed a 24-molecule supercell of ice XII to mimic its real structure. We focused on hydrogen bond (HB) vibrational modes in the translation band using first-principles density functional theory (DFT). Our simulated results were in good agreement with inelastic neutron scattering experiments. We found that the optical vibrational modes of HBs are composed of three main components. These are cluster vibrations in the lowest-frequency region, four-bond HB vibrations in the highest-frequency region, and two-bond modes in between. Although the experimentally recorded curve of ice XII is smooth in the translation region, our results support the proposal that two types of intrinsic HB vibrational modes are common in the ice family.

Comparative Analysis of Hydrogen-Bonding Vibrations of Ice VI.

It is difficult to investigate the hydrogen-bonding dynamics of hydrogen-disordered ice VI. Here, we present a comparative method based on our previous study of its counterpart hydrogen-ordered phase, ice XV. The primitive cell of ice XV is a 10 molecule unit, and the vibrational normal modes were analyzed individually. We constructed an 80 molecule supercell of ice VI to mimic the periodic unit and performed first-principles density functional theory calculations. As the two vibrational spectra show almost identical features, we compared the molecular translation vibrations. Inspired by the phonon analysis of ice XV, we found that the vibrational modes in the translation band of ice VI are classifiable into three groups. The lowest-strength vibration modes represent vibrations between two sublattices that lack hydrogen bonding. The highest-strength vibration modes represent the vibration of four hydrogen bonds of one molecule. The middle-strength vibration modes mainly represent the molecular vibrations of only two hydrogen bonds. Although there are many overlapping stronger and middle modes, there are only two main peaks in the inelastic neutron scattering (INS) spectra. This work explains the origin of the two main peaks in the far-infrared region of ice VI and illustrates how to analyze a hydrogen-disordered ice structure.

Computing Investigations of Molecular and Atomic Vibrations of Ice IX.

The normal modes of ice IX were investigated using the CASTEP code package, which is based on density functional theory. We found that the translational modes could be divided into three categories: four-bond vibrations, which possessed the highest energy; two-bond vibrations, which possessed the medium energy; and cluster vibrations with the lowest energy. The former two categories represent monomers vibrating against neighbors and present as two distinct peaks in many ice phases recorded in inelastic neutron-scattering experiments. It is typically difficult to assign the molecular vibration peaks in the far infrared region. The method we developed to analyze the normal modes, especially in the translation band of ice IX, provided physical insights into the vibrational spectrum of ice.

[Relationship between brainstem auditory evoked potential and serum neuron-specific enolase in neonates with asphyxia].

OBJECTIVE: To study the correlation between brainstem auditory evoked potential (BAEP) and serum neuron-specific enolase (NSE) in neonates with asphyxia and explore the role of NSE in the evaluation of hearing impairment following asphyxia. METHODS: Fifty-two term neonates with asphyxia, including 38 cases of simple asphyxia (mild: 23 cases; severe: 15 cases) and 14 cases of asphyxia complicated by hypoxic-ischemic encephalopathy (HIE), were enrolled. In the double-blind trial, BAEP and NSE were simultaneously detected 7 days after birth. The patients who did not pass BAEP test received another BAEP and NSE examinations 3 months after birth. Thirty healthy term neonates served as normal control group. RESULTS: Of the 52 neonates with asphyxia, 50.0% and 21.2% of patients failed the initial and the second BAEP tests, respectively. The detection rates of BAEP anomalies in the simple severe asphyxia group in the initial and the second tests (63.3% and 26.3%, respectively) were significantly higher than those in the simple mild asphyxia group (36.9% and 5.9%, respectively)(P<0.05). The neonates with asphyxia complicated by HIE showed a higher detection rate of BAEP anomalies in the second test compared with the asphyxiated neonates without HIE (31.3% vs 16.7%; P<0.05). Mean serum NSE levels in asphyxiated neonates were significantly higher than those in normal controls (<0.01). There were significant differences in serum NSE levels between the neonates with mild and severe asphyxia (26.70+/-2.34 microg/L vs 17.18+/-3.16 microg/L; P<0.01). The asphyxiated neonates with HIE had serum NSE levels similar to the simple severely asphyxiated neonates. Serum NSE levels in patients who failed the initial BAEP test were significantly higher than those who passed the test (25.69+/-4.12 microg/L vs 17.15+/-3.09 microg/L; <0.01). Serum NSE levels had a positive correlation with wave V reaction threshold detected in the BAFP test (<0.05). CONCLUSIONS: The serum level of NSE is closely correlated with BAEP, and it may be useful to the evaluation of the hearing impairment and the outcome in neonates with asphyxia.

[Etiology and high risk factors of neonatal ventilator-associated pneumonia].

OBJECTIVE: Ventilator-associated pneumonia (VAP) is a common nosocomial infection and is responsible for a very high mortality in neonatal intensive care unit (NICU) patients. This study was designed to investigate the etiology and high risk factors of neonatal VAP. METHODS: The clinical data of 106 critical neonates who were treated with mechanical ventilator between 2003 and 2005 were studied retrospectively. RESULTS: Of the 106 neonates, 84 received mechanical ventilation for > or = 48 hrs. Thirty-five (41.7%) out of the 84 patients developed VAP. Univariate analysis showed that gestational age, duration of mechanical ventilation, reintubation, birth weights, primary lung disease and gamma globulin administration were associated with the development of VAP (P < 0.05). Multivariate stepwise logistic regression analysis showed that primary lung disease (OR=3.671, 95% CI=1.0-13.45, P < 0.05), duration of mechanical ventilation (OR=4.945, CI=1.51-16.21, P < 0.01), reintubation (OR=7.721, 95% CI=2.31-25.85, P < 0.01) and high-dose gamma globulin administration (OR=5.520, 95%CI=2.08-16.26, P < 0.01) were predicted factors for the development of VAP. The detection rate of gram negative bacilli (76.9%) was the highest, followed by gram positive coccus (17.9%) in VAP patients. CONCLUSIONS: Opportunistic drug-resistant bacteria are common pathogens for neonatal VAP. The risk of VAP is multifactorial, including external medical environments and patients' internal agents.