Increase In Cavity Size Research Articles

Controlled fabrication and microwave absorbing mechanism of hollow Fe3O4@C microspheres

Uniform core-shell SiO2@Fe3O4@C microspheres were prepared by a one-step hydrothermal method with SiO2 microspheres as the template, and the hollow Fe3O4@C (HFC) microspheres were achieved via etching SiO2 template. By changing the sizes of SiO2 microspheres, a series of HFC microspheres with variable cavity sizes were obtained to study the relationship between cavity size and microwave absorbing (MA) performance for the first time. The morphology and structure of samples were characterized in detail. The results showed that the MA performance of HFC sample depended on its cavity size. In particular, the hollow structure was good for improving MA performance and could make MA move to the high-frequency region. More importantly, as the cavity size increases, the resonance frequency of HFC-i (i=1, 2, 3, 4) samples moved to a low frequency, and the optimal matching thickness of HFC-i samples was increasing. Among all HFC-i samples, HFC-3 showed the most excellent MA performance, which could be mainly explained by the quarter-wavelength matching model, intrinsical magnetic and dielectric loss. Furthermore, the MA performance of HFC mixture blended by the equal mass fraction of HFC-2, HFC-3 and HFC-4 was the comprehensive results of three HFC-i samples. All the above suggested that the cavity size in HFC sample had a great influence on the MA performance.

Rearing Light Intensity Affects Inner Retinal Pathology in a Mouse Model of X-Linked Retinoschisis but Does Not Alter Gene Therapy Outcome.

PurposeTo test the effects of rearing light intensity on retinal function and morphology in the retinoschisis knockout (Rs1-KO) mouse model of X-linked retinoschisis, and whether it affects functional outcome of RS1 gene replacement.MethodsSeventy-six Rs1-KO mice were reared in either cyclic low light (LL, 20 lux) or moderate light (ML, 300 lux) and analyzed at 1 and 4 months. Retinal function was assessed by electroretinogram and cavity size by optical coherence tomography. Expression of inward-rectifier K+ channel (Kir4.1), water channel aquaporin-4 (AQP4), and glial fibrillary acidic protein (GFAP) were analyzed by Western blotting. In a separate study, Rs1-KO mice reared in LL (n = 29) or ML (n = 27) received a unilateral intravitreal injection of scAAV8-hRs-IRBP at 21 days, and functional outcome was evaluated at 4 months by electroretinogram.ResultsAt 1 month, no functional or structural differences were found between LL- or ML-reared Rs1-KO mice. At 4 months, ML-reared Rs1-KO mice showed significant reduction of b-wave amplitude and b-/a-wave ratio with no changes in a-wave, and a significant increase in cavity size, compared to LL-reared animals. Moderate light rearing increased Kir4.1 expression in Rs1-KO mice by 4 months, but not AQP4 and GFAP levels. Administration of scAAV8-hRS1-IRBP to Rs1-KO mice showed similar improvement of inner retinal ERG function independent of LL or ML rearing.ConclusionsRearing light conditions affect the development of retinal cavities and post-photoreceptor function in Rs1-KO mice. However, the effect of rearing light intensity does not interact with the efficacy of RS1 gene replacement in Rs1-KO mice.

Electrocardiographic Changes Induced by Endurance Training and Pubertal Development in Male Children

Training-induced electrocardiographic changes are common in adult athletes. However, a few data are available on electrocardiogram (ECG) in preadolescent athletes and little is known about the potential changes induced by training on 12-lead electrocardiogram (ECG) at rest. Twelve-lead ECGs at rest and complete echocardiographic examinations were performed in 94 children (57 endurance athletes, 37 sedentary controls; mean age 10.8 ± 0.2 and 10.2 ± 0.2years, respectively) at baseline and after 5months of growth and training in athletes and of natural growth in controls. At baseline, athletes had lower heart rate at rest compared with controls (p= 0.046) and a further decrease was observed after training (p <0.0001). An incomplete right bundle branch block was found in 19% of athletes and 15% of controls (p= 0.69) with no changes after training. Although none of the athletes showed negative T waves from V1 to V3, 6% of controls at baseline had T-wave inversion V1 to V3 with a decrease to 3% after 5months (p= 0.16). The early repolarization pattern did not differ between athletes and controls and was correlated with Tanner's scale score in the overall population both at first and second evaluation (R= 0.30, R= 0.27, p= 0.005, p= 0.012, respectively). No correlations were found between ECG and echocardiographic data. In conclusion, 12-lead ECG at rest is not substantially affected by training in children, despite a physiological increase in cavity size. Thus, in preadolescent athletes, 12-lead ECG at rest does not reflect exercise-induced morphologic remodeling and seems to be influenced more by sexual maturation than by training.

Photonic states mixing beyond the plasmon hybridization model

A study is performed on a photonic-state mixing-pattern in an insulator-metal-insulator cylindrical silver nanoshell and its rich variations induced by changes in the geometry and dielectric media of the system, representing the combined influences of plasmon coupling strength and cavity effects. This study is performed in terms of the photonic local density of states (LDOS) calculated using the Green tensor method, in order to elucidate those combined effects. The energy profiles of LDOS inside the dielectric core are shown to exhibit consistently growing number of redshifted photonic states due to an enhanced plasmon coupling induced state mixing arising from decreased shell thickness, increased cavity size effect, and larger symmetry breaking effect induced by increased permittivity difference between the core and the background media. Further, an increase in cavity size leads to increased additional peaks that spread out toward the lower energy regime. A systematic analysis of those variations for a silver nanoshell with a fixed inner radius in vacuum background reveals a certain pattern of those growing number of redshifted states with an analytic expression for the corresponding energy downshifts, signifying a photonic state mixing scheme beyond the commonly adopted plasmon hybridization scheme. Finally, a remarkable correlation is demonstrated between the LDOS energy profiles outside the shell and the corresponding scattering efficiencies.

Penetrative convection of water in cavities cooled from below

Transient natural convection in water-filled square enclosures with the bottom wall cooled at 0 °C, and the top wall heated at a temperature spanning from 8 to 80 °C, is studied numerically for different widths of the cavity in the hypothesis of temperature-dependent physical properties, starting from the initial condition of motionless fluid at the uniform temperature of the top wall. The sidewalls are assumed to be adiabatic. A computational code based on the SIMPLE-C algorithm is used to solve the system of the mass, momentum and energy transfer governing equations. The propagation of convective motion from the bottom toward the top of the enclosure is investigated up to the achievement of a steady-state or a periodically-oscillating asymptotic solution. It is found that the ratio between the penetration depth and the cavity size increases as the temperature of the heated top wall decreases and the cavity size increases. Moreover, when the configuration is such that the buoyancy force in the water layer confined between the cooled bottom wall and the density-inversion isotherm is of the order of that required for the onset of convection, the asymptotic solution is periodical. Finally, the coefficient of convection decreases with increasing both the cavity width and the imposed temperature difference. Dimensionless correlations are developed for the calculation of the heat transfer rate across the enclosure and the penetration depth.

Chromospheric seismology above sunspot umbrae

The acoustic resonator is an important model for explaining the three-minute oscillations in the chromosphere above sunspot umbrae. The steep temperature gradients at the photosphere and transition region provide the cavity for the acoustic resonator, which allows waves to be both partially transmitted and partially reflected. In this paper, a new method of estimating the size and temperature profile of the chromospheric cavity above a sunspot umbra is developed. The magnetic field above umbrae is modelled numerically in 1.5D with slow magnetoacoustic wave trains travelling along magnetic fieldlines. Resonances are driven by applying the random noise of three different colours---white, pink and brown---as small velocity perturbations to the upper convection zone. Energy escapes the resonating cavity and generates wave trains moving into the corona. Line of sight (LOS) integration is also performed to determine the observable spectra through SDO/AIA. The numerical results show that the gradient of the coronal spectra is directly correlated with the chromosperic temperature configuration. As the chromospheric cavity size increases, the spectral gradient becomes shallower. When LOS integrations is performed, the resulting spectra demonstrate a broadband of excited frequencies that is correlated with the chromospheric cavity size. The broadband of excited frequencies becomes narrower as the chromospheric cavity size increases. These two results provide a potentially useful diagnostic for the chromospheric temperature profile by considering coronal velocity oscillations.

Nonstandard cages in the formation process of methane clathrate: Stability, structure, and spectroscopic implications from first-principles

Endohedral CH(4)@(H(2)O)(n) (n = 16, 18, 20, 22, 24) clusters with standard and nonstandard cage configurations containing four-, five-, six-, seven-membered rings were generated by spiral algorithm and were systematically explored using DFT-D methods. The geometries of all isomers were optimized in vacuum and aqueous solution. In vacuum, encapsulation of methane molecules can stabilize the hollow (H(2)O)(n) cage by 2.31~5.44 kcal/mol; but the endohedral CH(4)@(H(2)O)(n) cages are still less stable than the pure (H(2)O)(n) clusters. Aqueous environment could promote the stabilities of the hollow (H(2)O)(n) cages as well as the CH(4)@(H(2)O)(n) clusters, and the CH(4)@(H(2)O)(n) clusters possess larger stabilization energies with regard to the pure (H(2)O)(n) clusters except for n = 24. The lowest energy structures of the CH(4)@(H(2)O)(20) and CH(4)@(H(2)O)(24) cages are identical to the building units in the crystalline sI clathrate hydrate. All of the low-energy cages (including both regular and irregular ones) have large structural similarity and can be connected by "dimer-insertion" operation and Stone-Wales transformation. Our calculation also showed that in the range of cluster size n = 16-24, the relative energies of cage isomers tend to decrease with increasing number of the adjacent pentagons in the oxygen skeleton structures. In addition to the regular endohedral CH(4)@(H(2)O)(20) and CH(4)@(H(2)O)(24) cage structures, some nonstandard CH(4)@(H(2)O)(n) (n = 18, 20, 22, 24) cages have lower energies and might appear during nucleation process of methane hydrate. For the methane molecules in these low-energy cage isomers, we found that the C-H symmetric stretching frequencies show a red-shift trend and the (13)C NMR chemical shifts generally move toward negative values as the cavity size increases. These theoretical results are comparable to the available experimental data and might help experimental identification of the endohedral water cages during nucleation.

Tumor Bed Dynamics After Surgical Resection of Brain Metastases: Implications for Postoperative Radiosurgery

To analyze 2 factors that influence timing of radiosurgery after surgical resection of brain metastases: target volume dynamics and intracranial tumor progression in the interval between surgery and cavity stereotactic radiosurgery (SRS). Three diagnostic magnetic resonance imaging (MRI) scans were retrospectively analyzed for 41 patients with a total of 43 resected brain metastases: preoperative MRI scan (MRI-1), MRI scan within 24 hours after surgery (MRI-2), and MRI scan for radiosurgery planning, which is generally performed ≤1 week before SRS (MRI-3). Tumors were contoured on MRI-1 scans, and resection cavities were contoured on MRI-2 and MRI-3 scans. The mean tumor volume before surgery was 14.23 cm3, and the mean cavity volume was 8.53 cm3 immediately after surgery and 8.77 cm3 before SRS. In the interval between surgery and SRS, 20 cavities (46.5%) were stable in size, defined as a change of ≤2 cm3; 10 cavities (23.3%) collapsed by >2 cm3; and 13 cavities (30.2%) increased by >2 cm3. The unexpected increase in cavity size was a result of local progression (2 cavities), accumulation of cyst-like fluid or blood (9 cavities), and nonspecific postsurgical changes (2 cavities). Finally, in the interval between surgery and SRS, 5 cavities showed definite local tumor progression, 4 patients had progression elsewhere in the brain, 1 patient had both local progression and progression elsewhere, and 33 patients had stable intracranial disease. In the interval between surgical resection and delivery of SRS, surgical cavities are dynamic in size; however, most cavities do not collapse, and nearly one-third are larger at the time of SRS. These observations support obtaining imaging for radiosurgery planning as close to SRS delivery as possible and suggest that delaying SRS after surgery does not offer the benefit of cavity collapse in most patients. A prospective, multi-institutional trial will provide more guidance to the optimal timing of cavity SRS.

Assessment of Heating Rate and Non-uniform Heating in Domestic Microwave Ovens

Due to the inherent nature of standing wave patterns of microwaves inside a domestic microwave oven cavity and varying dielectric properties of different food components, microwave heating produces non-uniform distribution of energy inside the food. Non-uniform heating is a major food safety concern in not-ready-to-eat (NRTE) microwaveable foods. In this study, we present a method for assessing heating rate and non-uniform heating in domestic microwave ovens. In this study a custom designed container was used to assess heating rate and non-uniform heating of a range of microwave ovens using a hedgehog of 30 T-type thermocouples. The mean and standard deviation of heating rate along the radial distance and sector of the container were measured and analyzed. The effect of the location of rings and sectors was analyzed using ANOVA to identify the best location for placing food on the turntable. The study suggested that the best location to place food in a microwave oven is not at the center but near the edge of the turntable assuming uniform heating is desired. The effect of rated power and cavity size on heating rate and non-uniform heating was also studied for a range of microwave ovens. As the rated power and cavity size increases, heating rate increases while non-uniform heating decreases. Sectors in the container also influenced heating rate (p < 0.0001), even though it did not have clear trend on heating rate. In general, sectors close to the magnetron tend to heat slightly faster than sectors away from the magnetron. However, the variation in heating rate among sectors was only 2 °C/min and considered not practically important. Overall heating performance such as mean heating rate and non-uniform heating did not significantly vary between the two replications that were performed 4 h apart. However, microwave ovens were inconsistent in producing the same heating patterns between the two replications that were performed 4 h apart.

Preferential interaction of charged alkali metal ions (guest) within a narrow cavity of cyclic crown ethers (neutral host): A quantum chemical investigation

The binding interaction of alkali metal ions (charged guest) within the narrow cavity of crown ethers (neutral host) of different cavity size has been studied using quantum chemical density functional theory. Different conformational structures, binding energies and various thermodynamic parameters of free crown ethers and their metal ion complexes have been determined with the B3LYP functional using a large split valence 6-311++G(d,p) basis set. Geometry optimization was performed using guess structures obtained from semi-empirical PM3 optimized structures without imposing any symmetry restriction. The calculated values of binding enthalpy increase with increase in cavity size, i.e., with increase in donor O atoms and are found to be in good agreement with gas phase experimental results. We have demonstrated the effect of micro-solvation on the binding interaction between the alkali metal ions (Li + and Na +) and the macrocyclic crown ethers by considering micro-solvated metal ions up to six water molecules directly attached to the metal ion. A metal ion exchange reaction involving the replacement of lithium ion in metal ion–crown ether complexes with sodium ion contained within a metal ion–water cluster serves as the basis for modeling binding preferences in solution. An attempt has been made to study the effect of micro-solvation on the binding interaction of metal ions with crown ethers by considering two water molecules attached to metal ion–crown ether complexes. The calculated O H stretching frequency of H 2O molecule in micro-solvated metal ion–crown complexes is less blue-shifted in comparison to hydrated metal ions. The calculated IR spectra can be compared with an experimental spectrum to determine the presence of micro-solvated metal ion–crown ether complexes in extractant phase.

Forces that stabilize membrane proteins

Understanding the energetics of molecular interactions is essential to addressing many of the central quests of biochemistry including protein structure prediction and design, relating structure to function, mapping evolutionary pathways, learning how mutations cause disease and drug design. Hydrogen bonding and Van der Waals packing are two of the fundamental molecular forces that govern the protein structure and function. Because of technical challenges, however, there have been no quantitative tests of these forces in the context of large membrane proteins. While hydrogen-bonding has been widely regarded as an important force in a membrane environment because of the low dielectric constant of membranes and a lack of competition from water, our recent double-mutant cycle analysis shows that the average contribution of eight interhelical side-chain hydrogen-bonding interactions in bacteriorhodopsin is unexpectedly modest, providing only 0.6 kcal of energy per a mol of interaction on an average, which is quite similar to the strengths measured in soluble proteins. Van der Waals packing, on the other hand, is also thought to be important, as highlighted in number of transmembrane helix dimerization motifs that drive strong helix-helix association in the absence of polar residues by providing tight knob-into-hole interactions. Van der Waals strength, reported by the slope of the correlation found between the thermodynamic stability changes that we measured in six individual cavity-creating large-to-small hydrophobic side-chain mutants of bacteriorhodopsin and the increase in cavity size observed in the refined crystal structures of the corresponding mutant proteins, is indeed quite significant and also very similar to the contributions observed in a soluble protein. Weak hydrogen-bonding and significant Van der Waals packing should be reflected in considerations of membrane protein folding, dynamics, design, evolution and function.

Cavity growth simulation for superplastic deformation of tetragonal Zirconia polycrystal, 3Y‐TZP

AbstractA simulation based on cavity number ‐ radius distribution obtained from a scanning electron microscopy analysis was made to consider cavity growth rate and its mechanism during superplastic deformation of a tetragonal zirconia polycrystal (3Y‐TZP). It is found that (1) newly formed cavities grow very rapidly in an early stage of their growth process and then the growth rate becomes gradually slow with the increase in cavity size, and (2) the cavity growth process in the 3Y‐TZP is governed by the diffusion‐controlled mechanism.

Effect of cyclodextrin complexation in bromine addition to unsymmetrical olefins: evidence for participation of cyclodextrin hydroxyl groups

Multiple recognition by cyclodextrin in a bimolecular reaction, namely bromination of styrene, methyl cinnamate, phenylacetylene and allylbenzene, has been studied. Bromohydrin is obtained as a major product along with dibromide in the bromination of styrene and methyl cinnamate. The percentage of bromohydrin decreases as the cavity size increases. With phenylacetylene, bromophenylacetylene and phenacyl bromide are obtained in addition to the dibromides. In the bromination of cyclodextrin complexes of allylbenzene, the product distribution is the same as in solution bromination. The observed results demonstrate the efficiency of cyclodextrin in stabilizing the open carbocationic intermediate and thus provide chemical evidence for the participation of cyclodextrin hydroxyl groups.

Magnetic Dipole Moment from a One-Kiloton Underground Nuclear Explosion in a Cavity

This paper reports the results of numerical modeling of the magnetic dipole moment produced by displacement of the Earth's magnetic field in a one‐kiloton underground nuclear explosion in a cavity. It is shown that with increase in cavity size, the magnetic dipole moment increases, reaching 107 A · m2, which is approximately 200 times the magnetic dipole moment from a camouflet explosion. A factor of 100 decrease in the initial air density in cavities with radii of 10 and 20 m results in a reversal of the direction of the magnetic dipole moment vector.

A systematic evaluation of molecular recognition phenomena. 4. Selective binding of dicarboxylic acids to hexaazamacrocyclic ligands based on molecular flexibility.

The host-guest interaction between four hexaaza macrocyclic ligands (3,6,9,17,20,23-hexaazatricyclo[23.3.1.1]triaconta-1(29),11,13,15 (30),25(27)-hexaene (Bd), 3,6,9,16,19,22-hexaazatricyclo[22.2.2.2]triaconta-1(27),11(30),12,14(29),24(28),25-hexaene (P2), 3,7,11,19,23,27-hexaazatricyclo[27.3.1.1]tetratriaconta-1(33),13, 15,17(34),29,31-hexaene (Bn), 3,7,11,18,22,26-hexaazatricyclo[26.2.2.2]tetratriaconta-1(31),13(34),14,16(33),28(32),29-hexaene (P3)) and two dicarboxylic acids (oxalic acid, H2Ox; oxydiacetic acid, H2Od) have been investigated using potentiometric equilibrium methods. Ternary complexes are formed in aqueous solution as a result of hydrogen bond formation and Coulombic interactions between the host and the guest. In the [(H6P2)(Ox)]4+ complex those bonding interactions reach a maximum yielding a log KR6 of 6.08. This species has been further characterized by means of X-ray diffraction analysis showing that the oxalate guest molecule is situated inside the macrocyclic cavity of the P2 host. X-ray diffraction analysis has also been carried out for the complex [(H6Bn)(Od)2](Br)2.6H2O, where now the oxydiacetate is bonded to the host but outside the macrocyclic cavity. Competitive distribution diagrams and total species distribution diagrams are used to graphically illustrate the most salient features of these systems, which are the following: (a) The Bd and P2 ligands bind Ox significantly much more stronger than Od. This is clearly manifested for the P2:Ox:Od competitive system, where a selectivity of 92.5% in favor of the P2-Ox complexation against P2-Od is obtained at p[H] = 2.8. (b) No isomeric effect is found when comparing binding capacities of oxalate with two isomeric ligands such as P2 and Bd since their affinity to bind the substrate is relatively similar. (c) Bn and P3 ligands have a similar behavior as described in (a) for P2 and Bd except that due to the increase of cavity size the differentiation becomes smaller. (d) Less basic ligands containing two methylenic units Bd (log betaH6 = 40.42) and P2 (40.42) bind stronger to the substrates than those containing three methylenic units Bn (50.32) and P3 (50.64) even though their relative predominance depends on p[H].

High-speed directly modulated fabry-perot and distributed-feedback spot-size-converted lasers suitable for passive alignment, unisolated operation, and uncooled environments up to 85 °C

Semiconductor lasers with narrow far fields are highly desirable because they can be directly coupled to fiber with high-coupling efficiency, eliminating the cost of lenses and extra packaging. Because of their smaller size, they facilitate more compact transmitters, and since they can be used unpackaged, they enable complex integrated optoelectronic devices. We describe the design, fabrication, and performance characteristics of our family of spot-size-converted (SSC) devices with narrow far fields designed for directly modulated (2.5 and 10 Gb/s) uncooled (85/spl deg/C) use. The design consists of a conventional active region buried heterostructure laser coupled to an expander region (consisting of a loosely confining waveguide) through a laterally tapered etch of the active layers. This basic design achieves far fields of /spl sim/16/spl times/10 degrees, suitable for coupling /spl sim/50 percent of the emitted light into a flat cleaved fiber. Distributed feedback (DFB) 1.3- and 1.5-/spl mu/m devices, and 1.3-/spl mu/m Fabry-Perot (F-P) lasers have been implemented in this technology. The devices have dc thresholds from 8-12 mA at 25/spl deg/C and 35-45 mA at 85/spl deg/C, with peak power of >15 mWs over temperature, all similar to non-SSC devices with the same active regions. Both SSC F-Ps and DFBs demonstrate bandwidths of >7 GHz and wide-open eyes at 85/spl deg/C, and reliability suitable for uncooled use. With the DFB device, we also demonstrate a wide open 10-Gb/s eye pattern at room temperature. The laser on a submount demonstrates coupling to a fiber in a v-groove of /spl sim/25% using passive alignment, and sufficient tolerance to back reflection to enable transmission over at least 15 km with typical drive circuitry. Analysis shows that these lasers also have a factor of two improvements in alignment tolerance compared to standard devices in a typical lensed system. The expander impacts the dc and dynamic characteristics of the SSC F-P through the increase in cavity size. The dc and dynamic characteristics of SSC DFBs and standard DFBs are very similar, demonstrating that expander-related absorption and mode transition loss has been almost eliminated in this structure. The SSC-DFBs are, thus, the preferred device for high-speed applications. To our knowledge, the 1.3-/spl mu/m lasers described are the first SSC devices fully suited for use as an uncooled 2.5-Gb/s transmitters up to 85/spl deg/C. The combination of a tailored narrow far field with an edge emitting structure rivals vertical cavity lasers in alignment tolerance for low-cost packaging with superior dynamic and thermal performance.

Restoration removal with and without the aid of magnification.

This study aims to quantify any cavity size change following removal of tooth-coloured restorations in vitro using unaided vision and 2.6 x magnification. Occlusal composite restorations were removed under simulated clinical conditions and changes in cavity size were measured, blind to method, using standardized photographs. The outline of the cavity was digitized and its area was used as a surrogate for cavity size. The change in cavity size was determined for unaided vision and 2.6 x magnification, with any differences between the techniques investigated. There were significant increases in cavity size using both techniques and although the increase in size was less when magnification was used, the difference was not statistically significant. Cavity size changes significantly during re-restoration and the use of magnification may be of benefit for some clinicians in reducing the size of the change.

A correlation between the loss of hydrophobic core packing interactions and protein stability

The hydrophobic core packing in four-α-helical bundles appears to be crucial for stabilizing the protein structure. To examine the structural basis of hydrophobic stabilization, the crystal structures of the Leu→Val (L41V) and Leu→Ala (L41A) substitutions of the core residue Leu41 of the ROP protein have been determined. Both substitutions are destabilizing and lead to formation of cavities. The main responses to mutations are the collapse of the central part of the α-helix containing the site of mutation, shifts of internal water molecules, and in L41A, the trapping of a water molecule in a cavity engineered by the mutation. For both mutants, these effects limit the increase in cavity size to less than 10Å3, while an increase of 37Å3 and 100Å3 is expected for L41V and L41A, respectively, in the absence of any cavity size reducing effects. The mobility of internal side-chains is increased and in L41A, it reaches values typical for exposed residues. A parameter (Δnh) is introduced as a measure of the number of van der Waals contacts lost. For ROP, barnase and T4 lysozyme mutants, there is a good correlation between Δnh and the free energy of unfolding ΔΔG relative to wild-type protein. The Δnh value turns out to be more suitable for analysing structural and energetic responses to mutation than other parameter, such as cavity volumes and packing densities. Possible evolutionary implications of the ΔΔG versus Δnh relationship are discussed.

Swelling behavior of V–Fe binary and V–Fe–Ti ternary alloys

V–Fe binary alloys with different Fe concentrations, i.e., V–1, 3 and 5 at.% Fe, and V–5% Fe alloy added with 1, 3 and 5 at.% of Ti were irradiated in EBR-II at 380–615°C to about 11 dpa. TEM observation was performed after irradiation. A systematic increase in cavity size was observed with increasing iron concentration in the binary alloys, especially at 510°C and 615°C irradiation. On the other hand, the density of cavities decreased with increasing iron concentration and irradiation temperature. Maximum swelling in V–Fe system occurred between 500°C and 600°C and the amount of swelling was up to 30% at a damage level of 11 dpa. The alloy containing only 1% Fe already showed substantial swelling. The effect of titanium addition to the swelling was very remarkable. One atomic percent of titanium addition to V–5 at.% Fe significantly suppressed cavity formation, and 3 at.% of titanium addition entirely suppressed swelling. There seems to be a threshold titanium concentration for suppression of swelling in V–5 at.% Fe. Radiation-induced precipitation of titanium oxide may be one reason why titanium additions suppress the swelling in vanadium alloys. Homogeneous titanium oxide precipitates were not observed so that the titanium in solution is more likely to be playing an important role for suppression of swelling.

Free energy and entropy for inserting cavities in water: Comparison of Monte Carlo simulation and scaled particle theory results

The process of inserting cavities in water is studied with the aim of a better description of some of the terms necessary in continuum quantum mechanical models. Free-energy changes for the formation of soft and hard spherical cavities in TIP4P water have been computed by Monte Carlo (MC) simulation with statistical perturbation theory, up to a radius of 6 Å. The free-energy change for the formation of a hard sphere, ΔGcav, is obtained combining the ΔGsol of a soft repulsive sphere with the ΔG corresponding to the process of transforming the soft sphere into a hard one. Two definitions of hard-sphere repulsive potentials have been considered, one only based on the distance of oxygens from the center of the cavity, while the other also excludes hydrogens from the same region. Differences in free energies are significant. The cubic polynomial expression ΔGcav, obtained by extrapolating the exact scaled particle theory (SPT) expression for very small excluding cavities, gives results in agreement with MC, with effective “hard-sphere” diameter for water larger than 2.77 Å. The SPT prediction is compared with other treatments based on surface tension. It is shown that a properly chosen surface and an “effective” surface tension of water lead to a good agreement with MC ΔGcav without curvature or microscopic corrections. The “effective” surface tension of water turns out to be very close to the experimental value. Some different simple ways to extend SPT expression to nonspherical cavities have been compared, for a limited number of nonspherical convex cavities modeled as n interlocking spheres, meant to mimic n-alkanes in the all-staggered conformation. Entropy changes for soft cavities have been computed with two methods, i.e., combining free energy and enthalpy computations and by finite difference methods. Discrepancies between SPT predictions and MC results are significant. The calculated probability distributions of relevant angles of first hydration shell waters are consistent with orientations where no O–H or O–lone pair vector points towards the cavity. Their variation when the cavity size increases is mostly quantitative and only the broadening of the bands observed for the largest cavities might indicate the early stage of the transition to hydration patterns peculiar to an infinite hydrophobic surface.