Major Spectral Components Research Articles

Oil-in-Water Emulsions Probed Using Fluorescence Multivariate-Curve-Resolution Spectroscopy.

Hydrophobic surfaces in contact with aqueous media are omnipresent in nature. A plethora of key biological and physiological processes occur at the interface of immiscible fluids. Besides its fundamental importance, probing such interfaces is rather challenging, especially when one medium is bathed in the other. Herein, we demonstrate a fluorescence-based method that probes the oil-water interface and interfacial processes through surface dielectric perturbations. The fluorescence response of Nile Red is measured in hexadecane in water nanoemulsions. Three major spectral components appear: two from the bulk liquid media (hexadecane and water) and a distinct band at around 640 nm due to the interfacial component. Such spectra are deconvoluted using the multivariate-curve-resolution algorithm, and interface-correlated fluorescence spectra are attained. The influence of anionic sodium dodecylbenzenesulfonate (SDBS) and cationic cetyltrimethylammonium bromide (CTAB) surfactants on the oil-water interface is elucidated with concentration-dependent measurements. A charge-dependent spectral shift is observed. The interface correlated band at 641 nm for bare hexadecane nanoemulsions red shifts in the presence of anionic surfactants, indicating an apparent dielectric increase. In contrast, the same band gradually blue shifts with increasing cationic surfactant concentration, indicating an apparent interface dielectric decrease. Such a method can be utilized to probe alterations at interfaces beyond the oil/water interface.

Effects of Overload on Thermal Decomposition Kinetics of Cross-Linked Polyethylene Copper Wires.

During an overload fault in an energized wire, the hot metal core modifies the structure of the insulation material. Therefore, understanding the thermal decomposition kinetics of the insulation materials of the overloaded wire is essential for fire prevention and control. This study investigates the thermal decomposition process of new and overloaded cross-linked polyethylene (XLPE) copper wires using thermogravimetry-Fourier-transform infrared spectroscopy and cone calorimetry. The thermal decomposition onset temperature and activation energy of the overloaded XLPE insulation materials were reduced by approximately 15 K and 20 kJ mol-1, respectively, and its reaction mechanism function changed from D-ZLT3 to A2 (0 < α < 0.5). The FTIR shows that the major spectral components produced during the pyrolysis of the XLPE insulation material are C-H stretching, H2O, CO2, C-H scissor vibrations, and C=O and C=C stretching. Additionally, the four functional groups in the PE chains produced the spectral components in the following decreasing order of wavenumber: C-H stretching > CO2 > C-H scissor vibration > C=O and C=C stretching.

Influences of different environmental covariates on county-scale soil type identification using remote sensing images

The scientific selection of environmental covariates is an important factor that affects the accuracy of digital soil mapping (DSM).An investigation of the influences of different environmental covariates on soil type identification is vital to understand soil development and predictive soil mapping. In this study, the soil groups in the typical plain and hilly areas of the Jiaodong Peninsula in China were taken as the objects of investigation. Based on five environmental characteristics and remotely sensed indexes (texture, terrain, biology, major spectral components and moisture), 21 covariates sourced from Landsat 8 remote sensing images and a digital elevation map were utilized for the predictive mapping of soils. The identification accuracies of the soil groups were acquired through maximum likelihood classification, and the relevant environmental factors that are important for soil mapping and the influence of different environmental covariates on soil mapping were explored. The results show that texture features had the greatest influence on DSM, followed by terrain, major spectral components, moisture and biological factors. The single environmental covariate with the greatest impact on DSM was the texture entropy parameter. For areas containing plain and hilly landforms, the entropy, elevation, slope, normalized difference vegetation index (NDVI), third principal component (PC3) and normalized difference moisture index (NDMI) indicators compose the optimal covariate combination for soil identification. Clarifying the impacts of different environmental covariates on DSM can improve the soil classification applicability and accuracy. The environmental covariates discussed in this study would be useful in similar environmental areas and would provide a reference for DSM.

Determination of absorption coefficients and Urbach tail depth of ZnO below the bandgap with two-photon photoluminescence.

In this article, we demonstrate a novel approach to determine the absorption coefficient of ZnO below the bandgap via measuring the self-absorption (SA) effect on the two-photon luminescence (TPL) spectrum of the ZnO bulk crystal rod at cryogenic temperature. Under a geometric configuration of side-excitation and front-detection, the intensities of several major spectral components of TPL spectra of ZnO can be decisively tuned by precisely varying the transmitting distance of luminescence signal, so that the absorption coefficients at different wavelengths can be determined on the basis of Beer-Lambert law. Furthermore, the peak position of donor bound exciton luminescence exhibits a unique redshift tendency with increasing the transmitting distance. Starting from the product of Lorentzian lineshape function and exponential absorption edge of Urbach tail, an analytical formula is derived to quantitatively interpret the experimental redshift characteristic with the transmitting distance. The energy depth of Urbach tail of the studied ZnO crystal is deduced to be ∼13.3 meV. In principle, this new approach can be used to determine absorption coefficient of any luminescent solids as long as the SA effect happens.

Flow noise identification using acoustic emission (AE) energy decomposition for sand monitoring in flow pipeline

In pipelines used for petroleum production and transportation, sand particles may be present in the multi-phase flow of oil and gas and water. The Acoustic Emission (AE) measurement technique is used in the field of sand monitoring and detection in the oil and gas industry. However, as the AE signals recorded are strongly influenced by flow conditions in the pipe, identification of sand particle related signals or events remain a significant challenge in interpretation of AE signals. Therefore, a systematic investigation of sand particle impact AE energy measurements, using a sensor mounted on the outer surface of a sharp bend in a carbon steel pipe, was carried out in the laboratory to characterise flow signals using a slurry impingement flow loop test rig. A range of silica sand particles fractions of mean particle size (212–710 μm) were used in the flow with particle nominal concentration between (1 and 5 wt.%) while the free stream velocity was changed between (4.2 and 14 ms−1).A signal processing technique was developed in which the total AE energy associated with particle-free water impingement was divided into static and oscillated parts and a demodulated frequency analysis was carried out on the oscillated part to identify major spectral components and hence the sources of AE signals. A simple theoretical model for water impingement AE signals was then developed to show the dependence of AE energy components on different flow speeds. A similar decomposition of AE energy into static and oscillatory components was used to analyse AE signals for particle-laden flows. The effect of flow speed on the spectral AE energy for different sand concentrations and particle size fractions was investigated and the results show that the 100 Hz band is attributed to mechanical noise, the 42 Hz band is due to fluid turbulence and the dominant band is broad oscillated component.The AE energy decomposition method together with the water impingement model and coupled with spectral peaks filtering enable isolation of AE energy associated with particle impact from other AE sources and noise and, hence, the proposed decomposition approach can enhance the interpretation of AE data in pipeline flows.

Characteristics of a Transactive Phenomenon in Relationships among Older Adults with Dementia, Nurses as Intermediaries, and Communication Robot

Healthcare for older adults with dementia is an important healthcare problem in Japan and in other developed countries. Importantly, healthcare workers in Japan are also getting older. In order to address solutions to this problem, using robots is being realized and is starting to assist healthcare and welfare practice needs. The aim of this study was to identify the characteristics of a transactive phenomenon in relationships among older adults with dementia, with nurses as intermediaries and with a cognitive skill-aid robot. Subjects were two institutionalized older adults who were diagnosed with dementia using Hasegawa’s Dementia Scale-Revised; a Kabochan (Nodding Kabochan) fixed with a remote-controlled speaker, Pechat (Kabochan with Pechat). Measurements of autonomic nervous activity were done using wearable electrocardiography attached to the subjects for four hours. Heart Rate Variability data were assessed at various frequency bands using a HRV software tool. In a continuously recorded data, interbeat (R-R) intervals were obtained for a 1-min segment using the maximum entropy method. In this study, the two major spectral components of HRV, the variances of the low-frequency (LF: 0.04 - 0.15 Hz) band and high-frequency (HF: 0.15 - 0.4 Hz) band, were calculated. Activities and behaviors of subjects transacting with Kabochan were observed by the expert nurses and video-recorded. Throughout the transaction period, observations were recorded of patients’ behavior, words uttered and over-all contents of the transactive conversation with the Kabochan or Kabochan with Pechat. Identified characteristics were transactive relationship phenomenon; changes in autonomic nervous system activity of persons with dementia are expressed as per one minute, linguistic response of elderly people, transactive relations among Kabochan, Kabochan with Pechat, and nurses as intermediaries. These were exhibited as Figures: Situation 1, A Sense of Fear, Situation 2, A Pleasant Sensation, and Situation 3, Misunderstanding and Confusion. It also showed that autonomic nervous system activity of persons with communication skills is actively changing in older adults with dementia. Conversation of adding Pechat to the Kabochan illustrated that nurses as intermediaries showed emotional conversations as established by effectively manipulating the Pechat. Also, it was revealed that if Kabochan with Pechat uttered words about patient’s personal information in a conversation, the patient felt a sense of fear. The researchers suggest that when developing future communication robot for elderly with dementia, it is necessary to consider, for an effective conversation, transactive relationships including nurses as intermediaries. The role functions of these intermediaries have been shown of high versatility, indicating that situations such as these can also be controlled by other healthcare providers such as by occupational therapists.

Computer analysis of vibrational spectra of aqueous ethanol solutions

Results of decomposition of vibrational spectra for aqueous ethanol solutions into components in the region of hydroxyl group stretching vibrations are presented. The infrared light absorption and Raman scattering spectra are investigated for alcohol concentrations in the solution changing from 0 to 90 mass %. Methods of higher derivatives and genetic algorithms together with the simplex method are used to investigate the OH stretching vibrational band contour. Independent methods of spectral structure resolution demonstrate good agreement in the number of the major spectral components as well as in the dependences of the peak wavenumbers, band widths, and amplitudes of spectral components on the ethanol concentration in water. The observed changes in the shape of the spectral contour for OH stretching vibration and, therefore, its components are explained in terms of the hydrogen bonding in non-electrolyte/water mixtures.

BROADBAND SPECTRAL ANALYSIS OF THE GALACTIC RIDGE X-RAY EMISSION

Detailed spectral analysis of the Galactic X-ray background emission, or the Galactic Ridge X-ray Emission (GRXE), is presented. To study the origin of the emission, broad-band and high-quality GRXE spectra were produced from 18 pointing observations with Suzaku in the Galactic bulge region, with the total exposure of 1 Ms. The spectra were successfully fitted by a sum of two major spectral components; a spectral model of magnetic accreting white dwarfs with a mass of 0.66 (0.59-0.75) solar, and a softer optically-thin thermal emission with a plasma temperature of 1.2-1.5 keV which is attributable to coronal X-ray sources. When combined with previous studies which employed high spatial resolution of the Chandra satellite (e.g. Revnivtsev et al. 2009, Nature), the present spectroscopic result gives another strong support to a scenario that the GRXE is essentially an assembly of numerous discrete faint X-ray stars. The detected GRXE flux in the hard X-ray band was used to estimate the number density of the unresolved hard X-ray sources. When integrated over a luminosity range of ~10^30-10^34 erg/s, the result is consistent with a value which was reported previously by directly resolving faint point sources.

Spectral characterization of the recombinant mouse tumor suppressor 101F6 protein

Tumor suppressor protein 101F6, a gene product of the 3p21.3 (human) and 9F1 (mouse) chromosomal region, has recently been identified as a member of the cytochrome b561 (Cyt-b561) protein family by sequence homology. The His(6)-tagged recombinant mouse tumor suppressor Cyt-b561 protein (TSCytb) was recently expressed in yeast and purified, and the ascorbate reducibility was determined. TSCytb is auto-oxidizable and has two distinct heme b centers with redox potentials of approximately 40 and approximately 140 mV. Its split alpha-band in the dithionite-reduced spectrum at both 295 and 77 K is well resolved, and the separation between the two alpha-peaks is approximately 7 nm (approximately 222 cm(-1)). Singular value decomposition analysis of the split alpha-band in the ascorbate-reduced spectra revealed the presence of two major spectral components, each of them with split alpha-band but with different peak separations (6 and 8 nm). Similar minor differences in peak separation were obtained when the split alpha-bands in ascorbate-reduced difference spectra at low (<1 mM) and high (>10 mM) ascorbate concentrations were analysed. According to low-temperature electron paramagnetic resonance (EPR) spectroscopy, the two heme b centers are in the low-spin ferric state with maximum principal g values of 3.61 and 2.96, respectively. These values differ from the ones observed for other members of the Cyt-b561 family. According to resonance Raman spectroscopy, the porphyrin rings are in a relaxed state. The spectroscopic results are only partially in agreement with those obtained earlier for the native chromaffin granule Cyt-b561.

Analysis of electron spin resonance spectra of irradiated gingers: Organic radical components derived from carbohydrates

Electron spin resonance (ESR) spectral characterizations of gingers irradiated with electron beam were studied. Complex asymmetrical spectra (near g=2.005) with major spectral components (line width=2.4 mT) and minor signals (at 6 mT apart) were observed in irradiated gingers. The spectral intensity decreased considerably 30 days after irradiation, and continued to decrease steadily thereafter. The spectra simulated on the basis of characteristics of free radical components derived from carbohydrates in gingers are in good agreement with the observed spectra. Analysis showed that shortly after irradiation the major radical components of gingers were composed of radical species derived from amylose and cellulose, and the amylose radicals subsequently decreased considerably. At 30 days after irradiation, the major radical components of gingers were composed of radical species derived from cellulose, glucose, fructose or sucrose.

Effects of Vegetable Containing Gamma-Aminobutyric Acid on the Cardiac Autonomic Nervous System in Healthy Young People

The aim of this study was to investigate the effects of vegetable tablets containing Gamma-Aminobutyric Acid (GABA) intake on cardiovascular response and the autonomic nervous system in young adults. In a double-blind, randomized controlled trial, 7 healthy subjects were assigned to take vegetable tablets (10 g/trial) or control tablets (10 g/trial). We measured heart rate (HR), systolic and diastolic blood pressure, stroke volume, cardiac output, total peripheral resistance index, and the low- and high-frequency oscillatory components of heart rate variability (HRV). Two major spectral components were examined at low-frequency (LF: 0.04-0.15 Hz) and high-frequency (HF: 0.15-0.4 Hz) bands to indicate HRV. There were significant interactions in HR (p<0.01) and in LF/HF of HRV (p<0.05). HR increased after intake of control tablets, but not after that of vegetable tablets. LF/HF increased rapidly after intake of control tablets and rose slightly after vegetable tablet intake. There was no significant difference between the vegetable and control tablet trials in stroke volume, cardiac output, total peripheral resistance, systolic or diastolic blood pressure, HF, or LF. In conclusion, these results suggest the possibility that single administration of vegetable tablets containing GABA suppresses the sympathetic nervous activity leading to an elevation of blood pressure.

Positron Annihilation Lifetime Study of Vacancies in Nb-Doped Rutile

Nb-doped rutile produced by sintering at 1400°C in an air atmosphere led to a monotonic increase of the shortest τ1 lifetime of the major spectral component from 0.17 to 0.25 ns in the 22Na positron annihilation lifetime spectrum as the Nb doping level was progressively increased to 0.12 formula units, at which stage TiNb2O7 was observed as a second phase. The charge compensators for Nb5+ substituting for Ti4+ are indicated as cation vacancies on the basis of the increase of τ1.

Acute Toluene Exposure and Rat Visual Function in Proportion to Momentary Brain Concentration

Acute exposure to toluene was assessed in two experiments to determine the relationship between brain toluene concentration and changes in neurophysiological function. The concentration of toluene in brain tissue at the time of assessment was estimated using a physiologically based pharmacokinetic model. Brain neurophysiological function was measured using pattern-elicited visual evoked potentials (VEP) recorded from electrodes located over visual cortex of adult male Long-Evans rats. In the first experiment, VEPs were recorded before and during exposure to control air or toluene at 1000 ppm for 4 h, 2000 ppm for 2 h, 3000 ppm for 1.3 h, or 4000 ppm for 1 h. In the second experiment, VEPs were recorded during and after exposure to clean air or 3000 or 4000 ppm toluene. In both experiments, the response amplitude of the major spectral component of the VEP (F2 at twice the stimulus rate in steady-state responses) was reduced by toluene. A logistic function was fit to baseline-adjusted F2 amplitudes from the first experiment that described a significant relationship between brain toluene concentration and VEP amplitude deficits. In the second experiment, 3000 ppm caused equivalent VEP deficits during or after exposure as a function of estimated brain concentration, but 4000 ppm showed a rapid partial adaptation to the acute effects of toluene after exposure. In general, however, the neurophysiological deficits caused by acute toluene exposure could be described by estimates of the momentary concentration of toluene in the brain at the time of VEP evaluation.

Mars Express High Resolution Stereo Camera spectrophotometric data: Characteristics and science analysis

The High Resolution Stereo Camera (HRSC) on the Mars Express (MEx) spacecraft in orbit about Mars is delivering images of the Mars surface and atmosphere from its high‐inclination, elliptical orbit that are intended to cover most of the Mars surface by the end of the mission. These are acquired in four specific spectral passbands that sample the scene at different parts of the extended visual spectrum from near 0.4 μm to about 1μm and in five additional channels, four used for stereo and one nadir, that use the same fifth spectral passband. These channels view from different angles and can be used for photometric and spectral analysis. The data allow a variety of studies of the surface and atmosphere of Mars, but these require detailed understanding of the data characteristics, as there are several effects, including of the observation geometry and the atmosphere, that need to be treated. This article is a report to the science community on the current understanding of the HRSC color data after an initial analysis and also a demonstration of their capabilities for study of Mars, which, from this study, appear to be considerable. We first discuss the characteristics and calibration of the HRSC spectral data. The atmospheric influence on the photometric appearance of the surface materials is explored, and methods of compensating are considered. Reflectances are calculated for surface units by assuming the dark material is basalt and scaling the entire HRSC scene using a laboratory basalt spectrum for the selected dark material area; the results and the correction factors for different orbits are compared. We present several examples of what could become a large volume of future science results utilizing the HRSC spectrophotometric data in conjunction with photo‐interpretation. For example, we find relatively few but very important distinct spectral components at the HRSC resolution, including what we interpret as iron oxide‐rich material, unoxidized basalt, and polar ice, consistent with past works. The major spectral components are distributed in ways that suggest compositional mixing and the need to revise the current geologic understanding of major regions.

Investigation on the electronically excited state properties of multiwalled carbon nanotube (MDDA) in solution

Sub-microsecond time-resolved absorption spectroscopy has been used to study the electronically excited state behavior of soluble multiwalled carbon nanotube (MWNTsCON((CH 2 ) 9 -CH 3 ) 2 , denoted as MDDA) in chloroform, toluene and cyclohexane. Following pulsed photo-excitation of MDDA at 355 nm, three major spectral components are clearly identified with the help of global analysis carried out over 7 representative kinetics curves from 450 to 700 nm. The solvent dependence of decay associated difference spectra (DADS) and the corresponding lifetimes help to assign these transient species to singlet state (S 1 ), triplet state (T 1 ) and charge-separated state (CS), respectively. Preliminary discussion had been made to explore the involved photophysical and electron transfer processes.

Histamine at high dilution reduces spectral density in delta band in sleeping rats

Histamine is a central neurotransmitter, it increases arousal via H 1 receptors. This study examines the effect of ultra-diluted histamine on arousal through changes in the sleep pattern of Wistar rats. The spectral density in delta (0.5–2.5 Hz) band, one of the three major spectral components of the sleep-electroencephalogram, was analyzed against time. Rats were randomized to receive histamine 30c (histamine 30c, 0.05 ml every 20 min during the first 2 h orally), histamine intraperitoneal pre-treatment/histamine 30c (histamine 6 mg/kg i.p., followed by histamine 30c) or solvent control. The mean delta band spectral density was lower in the histamine 30c and histamine pretreatment/histamine 30c groups than the control group. Significant differences between histamine 30c and baseline during the first 2 h imply an immediate effect. These results also suggest a dynamic process in which the system spontaneously evolves between two locally stationary states according to a power law. From the time perspective, the system approaches, asymptotically, an equifinal state.

Triplet Excitation Transfer between Carotenoids in the LH2 Complex from Photosynthetic Bacterium Rhodopseudomonas palustris

We have studied, by means of sub-microsecond time-resolved absorption spectroscopy, the triplet-excited state dynamics of carotenoids (Cars) in the intermediate-light adapted LH2 complex (ML-LH2) from Rhodopseudomonas palustris containing Cars with different numbers of conjugated double bonds. Following pulsed photo-excitation at 590 nm at room temperature, rapid spectral equilibration was observed either as a red shift of the isosbestic wavelength on a time scale of 0.6-1.0 mus, or as a fast decay in the shorter-wavelength side of the T(n)<--T(1) absorption of Cars with a time constant of 0.5-0.8 mus. Two major spectral components assignable to Cars with 11 and 12 conjugated double bonds were identified. The equilibration was not observed in the ML-LH2 at 77 K, or in the LH2 complex from Rhodobacter sphaeroides G1C containing a single type of Car. The unique spectral equilibration was ascribed to temperature-dependent triplet excitation transfer among different Car compositions. The results suggest that Cars of 11 and 12 conjugated bonds, both in close proximity of BChls, may coexist in an alpha,beta-subunit of the ML-LH2 complex.

Microscopic Structure of Er-Related Optically Active Centers in Si

AbstractA successful observation and analysis of the Zeeman effect on the near 1.54 μm photoluminescence spectrum in Er-doped crystalline MBE-grown silicon are reported. A clearly resolved splitting of 5 major spectral components was observed in magnetic fields up to 5.5 T. Based on the analysis of the data the symmetry of the dominant optically active center was conclusively established as orthorhombic I (C2v), with g‼≈18.4 and g⊥≈0 in the ground state. The fact that g⊥≈0 explains why EPR detection of Er-related optically active centers in silicon may be difficult. Preferential generation of a single type of an optically active Er-related center in MBE growth confirmed in this study is essential for photonic applications of Si:Er.

Effects of aldehyde dehydrogenase-2 genotype on cardiovascular and endocrine responses to alcohol in young Japanese subjects

The present study was designed to investigate the effects of aldehyde dehydrogenase-2 (ALDH2) genotype on cardiovascular and endocrine responses to alcohol ingestion in young, healthy Japanese subjects. For this purpose, we monitored changes in the electrocardiogram (ECG), blood pressure (BP), finger blood flow (BF) and facial skin temperature (FST) during and after alcohol ingestion (0.4 ml/kg body weight). Spectral analyses of beat-to-beat variations of heart rate (HR), BP and BF were applied. Two major spectral components were examined at low frequency (LF: 0.04–0.15 Hz) and high frequency (HF: 0.15–10.4 Hz) bands for HR and BP variability (BPV). Significant effects for ALDH2 genotype were observed in HR variability (HRV) analysis; HF power of HRV was markedly depressed and the LF/HF ratio was significantly higher with alcohol in ALDH2-deficient (ND) subjects, while ALDH2-normal (NN) subjects did not display such changes. Analysis of BP variability showed increased LF and HF power after alcohol ingestion in the NN subjects, but there were no significant differences between genotypic groups. We also examined BF variability (BFV) in six major spectral components; power of the 0.8–2.2 Hz frequency band was significantly affected by genotype and higher power was observed in the ND subjects. Plasma concentrations of both epinephrine and norepinephrine increased after alcohol ingestion only in the ND subjects. Furthermore, plasma concentrations and urinary excretion of epinephrine, but not norepinephrine, were higher after alcohol ingestion in the ND than in the NN subjects. Blood acetaldehyde levels were about 10-fold higher in the ND than in the NN subjects although blood alcohol levels similarly increased in the ND and NN subjects. Our results also indicated that alcohol ingestion increased secretion of pituitary–adrenal hormones including ACTH, β-endorphin and cortisol in the ND subjects. The present results along with previous studies suggest that alcohol-induced tachycardia in the ND subjects was probably mediated by acetaldehyde-induced rise in epinephrine secretion from the adrenal medulla and/or changes in the autonomic nervous system. Alcohol-induced relative predominance of cardiac sympathetic activity in the ND subjects might be ascribed partly to increased norepinephrine secretion from sympathetic nerve terminals. Effects of acetaldehyde on these cardiovascular and endocrine systems were discussed in terms of their effects on the central nervous system.

Time Resolved Spectroscopy of Water in the Infrared: New Data and Discussion

Abstract We demonstrate sub-picosecond spectroscopy of an isotopic water mixture presenting strong evidence for four major spectral components within the OH-band of HDO in the solvent D2O peaked at approximately 3330 cm-1 (I), 3390 cm-1 (II), 3460 cm-1 (III), and 3520 cm-1 (IV). Species I and IV are. proposed to give rise for discrete components with local hexagone and weakly bound structures, respectively. The remaining species are most probably related to combination tones with hydrogen bridge bond vibrations. Furthermore we summarise the findings on the vibrational and spectral dynamics of water as determined by time-resolved IR-spectroscopy of HDO molecules dissolved at low concentration in D2O.