577 research outputs found
Protective clothing ensembles and physical employment standards
Physical employment standards (PESs) exist for certain occupational groups that also require the use of protective clothing ensembles (PCEs) during their normal work. This review addresses whether these current PESs appropriately incorporate the physiological burden associated with wearing PCEs during respective tasks. Metabolic heat production increases due to wearing PCE; this increase is greater than that due simply to the weight of the clothing and can vary two-fold among individuals. This variation negates a simple adjustment to the PES for the effect of the clothing on metabolic rate. As a result, PES testing that only simulates the weight of the clothing and protective equipment does not adequately accommodate this effect. The physiological heat strain associated with the use of PCEs is also not addressed with current PESs. Typically the selection tests of a PES lasts less than 20 minutes whereas the requirement for use of PCE in the workplace may approach one hour before cooling strategies could be employed. One option that might be considered is to construct a heat stress test that requires new recruits and incumbents to work for a predetermined duration while exposed to a warm environmental temperature, wearing the PCE
NMR shieldings from density functional perturbation theory: GIPAW versus all-electron calculations
We present a benchmark of the density functional linear response calculation
of NMR shieldings within the Gauge-Including Projector-Augmented-Wave method
against all-electron Augmented-Plane-Wavelocal-orbital and uncontracted
Gaussian basis set results for NMR shieldings in molecular and solid state
systems. In general, excellent agreement between the aforementioned methods is
obtained. Scalar relativistic effects are shown to be quite large for nuclei in
molecules in the deshielded limit. The small component makes up a substantial
part of the relativistic corrections.Comment: 3 figures, supplementary material include
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A novel heteroditopic terpyridine-pincer ligand as building block for mono- and heterometallic Pd(II) and Ru(II) complexes
A palladium-catalyzed Stille coupling reaction was employed as a versatile method for the synthesis of a novel terpyridine-pincer (3, TPBr) bridging ligand, 4'-{4-BrC6H2(CH2NMe2)(2)-3,5}-2,2':6',2 ''-terpyridine. Mononuclear species [PdX(TP)] (X = Br, Cl), [Ru(TPBr)(tpy)](PF6)(2), and [Ru(TPBr)(2)](PF6)(2), synthesized by selective metalation of the NCNBr-pincer moiety or complexation of the terpyridine of the bifunctional ligand TPBr, were used as building blocks for the preparation of heterodi- and trimetallic complexes [Ru(TPPdCl)(tpy)](PF6)(2) (7) and [Ru(TPPdCl)(2)]-(PF6)(2) (8). The molecular structures in the solid state of [PdBr(TP)] (4a) and [Ru(TPBr)(2)](PF6)(2) (6) have been determined by single-crystal X-ray analysis. Electrochemical behavior and photophysical properties of the mono-and heterometallic complexes are described. All the above di- and trimetallic Ru complexes exhibit absorption bands attributable to (MLCT)-M-1 (Ru -> tpy) transitions. For the heteroleptic complexes, the transitions involving the unsubstituted tpy ligand are at a lower energy than the tpy moiety of the TPBr ligand. The absorption bands observed in the electronic spectra for TPBr and [PdCl(TP)] have been assigned with the aid of TD-DFT calculations. All complexes display weak emission both at room temperature and in a butyronitrile glass at 77 K. The considerable red shift of the emission maxima relative to the signal of the reference compound [Ru(tpy)(2)](2+) indicates stabilization of the luminescent (MLCT)-M-3 state. For the mono- and heterometallic complexes, electrochemical and spectroscopic studies (electronic absorption and emission spectra and luminescence lifetimes recorded at room temperature and 77 K in nitrile solvents), together with the information gained from IR spectroelectrochemical studies of the dimetallic complex [Ru(TPPdSCN)(tpy)](PF6)(2), are indicative of charge redistribution through the bridging ligand TPBr. The results are in line with a weak coupling between the {Ru(tpy)(2)} chromophoric unit and the (non)metalated NCN-pincer moiety
Endothermic salts integrated in impermeable suits do not reduce heat strain during exercise
Wearing impermeable garments during work inherently leads to heat strain, even in cold
environments [1]. Phase change materials (mainly paraffinâs or salt [4]) may be used as a thermal
buffer (e.g. [2]) to reduce initial heat stress. Salts can also be used to absorb sweat, which may
enhance the cooling power from the skin.
Recently, specific encapsulated salts utilising KSCN (potassium thiocyanate) have been developed
that consume energy when the KSCN dissolves in water. The heat consumed when the KSCN
(present inside 150 g of capsules containing 60% KSCN salt) dissolves in water is 22410 J (249 J/g *
60% * 150 g). When this solving takes place over a period of 30 minutes, the average power
transfer is 12 W. One (1) g of KSCN-containing capsules absorbs close to 1 g of moisture. If we
assume that 150 g sweat extra can be evaporated from the skin, this yields an extra cooling power
of 182 W for 30 minutes. However this evaporated water from the skin is subsequently absorbed
by the KSCN in the capsules. During this absorption from the gas phase, the condensation heat is
released to the KSCN salt: about 182 W for 30 minutes. However, we hypothesise that this
condensation heat will be partly transferred to the body and partly to the environment [3],
providing a net benefit to the body.
Thus, the total cooling effect due to the salt capsules is composed of two parts:
âą The cooling effect of about 12 W due to the heat consumption by the dissolving of the salts in
water;
âą The cooling effect of maximal 182 W, which equals the difference between the evaporative
heat and the condensation heat. The latter is generated in the salt capsules that transfer part
of the heat to the environment.
The overall cooling effect should therefore be in between 12 W and 194 W.
The purpose of our study was to test the efficacy of a KSCN-based absorbing salt as a PCM for use
within impermeable protective clothing. We tested the PCM during 20 min of moderate exercise
in a hot (35°C, 40% relative humidity) environment, and hypothesized that thermal strain would be
lower in the PCM compared to the non-PCM condition
Thermoregulatory responses during competitive wheelchair rugby match play
The purpose of this study was to determine whether a playerâs physical impairment or activity profile was related to the amount of thermal strain experienced during wheelchair rugby match play. 17 elite wheelchair rugby players played a competitive match, whilst activity profiles, measures of core and skin temperature, heart rate and perceptual responses were taken. Players were divided into 2 groups depending on their physical impairment: players with a cervical spinal cord injury, (n=10) or non-spinal related physical impairment (n=7). Total distance was lower (4â842±324 vs. 5â541±316âm, p<0.01, ES=2.2) and mean speed slower (1.13±0.11 vs. 1.27±0.11âmâsâ1, p<0.03, ES=1.3) in players with a spinal cord injury. Yet, the change in core temperature (1.6±0.4 vs. 0.7±0.3°C, p<0.01, ES=2.5) was significantly greater in players with a spinal cord injury. In conclusion, players with a spinal cord injury were under greater thermal strain during wheelchair rugby match play, as a result of their reduced heat loss capacity, due to their physical impairment and not because of their activity profile
Spectral signatures of excess-proton waiting and transfer-path dynamics in aqueous hydrochloric acid solutions
Signatures of solvated excess protons in infrared difference absorption
spectra, such as the continuum band between the water bend and stretch bands,
have been experimentally known for a long time, but the theoretical basis for
linking spectral signatures with the microscopic proton-transfer mechanism so
far relied on normal-mode analysis. We analyze the excess-proton dynamics in ab
initio molecular-dynamics simulations of aqueous hydrochloric acid solutions by
trajectory-decomposition techniques. The continuum band in the 2000 - 3000
cm range is shown to be due to normal-mode oscillations of temporary
HO complexes. An additional prominent peak at 400 cm reports on
the coupling of excess-proton motion to the relative vibrations of the two
flanking water molecules. The actual proton transfer between two water
molecules, which for large water separations involves crossing of a barrier and
thus is not a normal mode, is characterized by two characteristic time scales:
Firstly, the waiting time for transfer to occur in the range of 200 - 300 fs,
which leads to a broad weak shoulder around ~100 cm, consistent with our
experimental THz spectra. Secondly, the mean duration of a transfer event of
about 14 fs, which produces a rather well-defined spectral contribution around
1200 cm and agrees in location and width with previous experimental
mid-infrared spectra
Strong Anisotropy in Liquid Water upon Librational Excitation using Terahertz Laser Fields
Tracking the excitation of water molecules in the homogeneous liquid is
challenging due to the ultrafast dissipation of rotational excitation energy
through the hydrogen-bonded network. Here we demonstrate strong transient
anisotropy of liquid water through librational excitation using single-color
pump-probe experiments at 12.3 THz. We deduce a third order response of chi^3
exceeding previously reported values in the optical range by three orders of
magnitude. Using a theory that replaces the nonlinear response with a material
response property amenable to molecular dynamics simulation, we show that the
rotationally damped motion of water molecules in the librational band is
resonantly driven at this frequency, which could explain the enhancement of the
anisotropy in the liquid by the external Terahertz field. By addition of salt
(MgSO4), the hydration water is instead dominated by the local electric field
of the ions, resulting in reduction of water molecules that can be dynamically
perturbed by THz pulses
The electronic structure of carbones revealed : insights from valence bond theory
In this contribution, we studied the OC-C bond in carbon suboxide and related allene compounds using the valence bond method. The nature of this bond has been the subject of debate, whether it is a regular, electron sharing bond or a dative bond. We compared the nature of this bond in carbon suboxide with the gold-CO bond in Au(CO)(2)(+), which is a typical dative bond, and we studied its charge-shift bond character. We found that the C-CO bond in carbon suboxide is unique in the sense that it cannot be assigned as either a dative or electron sharing bond, but it is an admixture of electron sharing and dative components, together with a high contribution of ionic character. These findings provide a clear basis for distinguishing the commonly found dative bonds between ligands and transition metals and the present case of what may be described as coordinative bonding to carbon
Improving the force field description of tyrosine-choline cation-Ï interactions : QM investigation of phenol-N(Me)ââș interactions
Cation-pi interactions between tyrosine amino acids and compounds containing N,N,N-trimethylethanolammonium (N(CH3)(3)) are involved in the recognition of histone tails by chromodomains and in the recognition of phosphatidylcholine (PC) phospholipids by membrane-binding proteins. Yet, the lack of explicit polarization or charge transfer effects in molecular mechanics force fields raises questions about the reliability of the representation of these interactions in biomolecular simulations. Here, we investigate the nature of phenol tetramethylammonium (TMA) interactions using quantum mechanical (QM) calculations, which we also use to evaluate the accuracy of the additive CHARIVIM36 and Drude polarizable force fields in modeling tyrosine-choline interactions. We show that the potential energy surface (PES) obtained using SAPT2+/aug-cc-pVDZ compares well with the large basis-set CCSD(T) PES when TMA approaches the phenol ring perpendicularly. Furthermore, the SAPT energy decomposition reveals comparable contributions from electrostatics and dispersion in phenol-TMA interactions. We then compared the SAPT2+/augcc-pVDZ PES obtained along various approach directions to the corresponding PES obtained with CHARMM, and we show that the force field accurately reproduces the minimum distances while the interaction energies are underestimated. The use of the Drude polarizable force field significantly improves the interaction energies but decreases the agreement on distances at energy minima. The best agreement between force field and QM PES is obtained by modifying the Lennard-Jones terms for atom pairs involved in the phenol-TMA cation-pi interactions. This is further shown to improve the correlation between the occupancy of tyrosine-choline cation-pi interactions obtained from molecular dynamics simulations of a bilayer-bound bacterial phospholipase and experimental affinity data of the wild-type protein and selected mutants
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