Slow Decay Rate Research Articles

TU‐A‐BRB‐02: Temporal Signal Stability of KCl:Eu2+ Storage Phosphor Dosimeters

Purpose: It is known that the PSL (photo‐stimulated luminescence) signal fades with time after x‐ray irradiation and eventually reaches a plateau. The purpose of this work is to determine whether x‐ray generated electrons stored in non‐dosimetric shallow traps can be liberated prior to dose readout. If so, we would achieve a rapid signal stabilization so the wait time could be shortened to, for example, one hour or less. Methods: Pellet‐style KCl: Eu2+ dosimeters were fabricated in‐house for this study. PSL signal stability after x‐ray irradiation was studied by interfering with a thermal annealing and optical annealing with near infra‐red light, respectively prior to dosimetric readout. Results: Without optical annealing, PSL faded with time at a rate of 13.6%/hr for the first 2 hrs and 6%/hr for the next 3 hrs after irradiation and eventually reached a fading rate of about 0.5%/hr after 12 hrs. PSL intensity decreased with increasing NIR optical annealing time; however, there was only marginal improvement in the PSL stabilization rate, indicating that the shallow electron traps that are responsible for the fast‐fading for the first few hours were not efficiently emptied. 15‐minute thermal annealing treatments at either 60 or 70°C stabilized the PSL to a slow decay rate of approximately 0.4%/hr over a time period of 24 hrs post irradiation. Moreover, 90% of PSL sensitivity can be retained. More stable PSL signal, 0.18%/hr and 0.08%/hr decay rate for 90 and 120°C thermal annealing, respectively, can be achieved at the expense of PSL sensitivity. Conclusions: Thermal annealing immediately after x‐ray irradiation is an effective way to remove electrons stored in the shallow traps. This study is expected to guide the future design of storage phosphor dosimeter readers, which could incorporate a thermal annealing pre‐read cycle. As a Result, a long wait time would be avoided.

Pivaloylmetals (tBu‐COM: M=Li, MgX, K) as Equilibrium Components

Short-lived pivaloylmetals, (H(3)C)(3)C-COM, were established as the reactive intermediates arising through thermal heterolytic expulsion of O=CtBu(2) from the overcrowded metal alkoxides tBuC(=O)-C(-OM)tBu(2) (M = MgX, Li, K). In all three cases, this fission step is counteracted by a faster return process, as shown through the trapping of tBu-COM by O=C(tBu)-C(CD(3))(3) with formation of the deuterated starting alkoxides. If generated in the absence of trapping agents, all three tBu-COM species "dimerize" to give the enediolates MO-C(tBu)=C(tBu)-OM along with O=CtBu(2) (2 equiv). A common-component rate depression by surplus O=CtBu(2) proves the existence of some free tBu-COM (separated from O=CtBu(2)); but companion intermediates with the traits of an undissociated complex such as tBu-COM & O=CtBu(2) had to be postulated. The slow fission step generating tBu-COMgX in THF levels the overall rates of dimerization, ketone addition, and deuterium incorporation. Formed by much faster fission steps, both tBu-COLi and tBu-COK add very rapidly to ketones and dimerize somewhat slower (but still fairly fast, as shown through trapping of the emerging O=CtBu(2) by H(3)CLi or PhCH(2)K, respectively). At first sight surprisingly, the rapid fission, return, and dimerization steps combine to very slow overall decay rates of the precursor Li and K alkoxides in the absence of trapping agents: A detailed study revealed that the fast fission step, generating tBu-COLi in THF, is followed by a kinetic partitioning that is heavily biased toward return and against the product-forming dimerization. Both tBu-COLi and tBu-COK form tBu-CH=O with HN(SiMe(3))(3), but only tBu-COK is basic enough for being protonated by the precursor acyloin tBuC(=O)-C(-OH)tBu(2) .

Optical properties of Mn in regrown GaN-based epitaxial layers

The memory effect and redistribution of manganese (Mn) into subsequently regrown GaN-based epitaxial layers by metalorganic chemical vapor deposition were revealed. Low-temperature up-converted photoluminescence (UPL) and the secondary ion mass spectrometry were performed on GaN-based epitaxial samples with and without Mn doping to study the effect of residual Mn on optical property. UPL emission, which originated from residual Mn doping in regrown InGaN quantum wells (QWs) because of the memory effect of the reactor, could be eliminated in an air-exposed and H2-baking manner prior to the regrowth of the QWs. Considerable residual Mn background level and slow decay rate of Mn concentration tail were also observed in the regrown epitaxial layers, which could be attributed to the memory effect or surface segregation and diffusion from the Mn-doped underlying layer during regrowth in the Mn-free reactor.

Abstracts of the 17th International Symposium on Bioluminescence and Chemiluminescence ‐ (ISBC 2012)

WARNING : The light-emitting molecular structures responsible for the chemiluminescence and fluorescence phenomena are not necessarily the same!

THEKEPLERLIGHT CURVES OF V1504 CYGNI AND V344 LYRAE: A STUDY OF THE OUTBURST PROPERTIES

We examine the Kepler light curves of V1504 Cyg and V344 Lyr, encompassing ~736 d at 1 min cadence. During this span each system exhibited ~64-65 outbursts, including six superoutbursts. We find that, in both systems, the normal outbursts between two superoutbursts increase in duration over time by a factor ~1.2-1.9, and then reset to a small value after the following superoutburst. In both systems the trend of quiescent intervals between normal outbursts is to increase to a local maximum about half way through the supercycle - the interval from one superoutburst to the next - and then to decrease back to a small value by the time of the next superoutburst. This is inconsistent with Osaki's thermal-tidal model, which predicts a monotonic increase in the quiescent intervals between normal outbursts during a supercycle. Also, most of the normal outbursts have an asymmetric, fast-rise/slower-decline shape, consistent with outbursts triggered at large radii. The exponential rate of decay of the plateau phase of the superoutbursts is 8 d/mag for V1504 Cyg and 12 d/mag for V344 Lyr. This time scale gives a direct measure of the viscous time scale in the outer accretion disk given the expectation that the entire disk is in the hot, viscous state during superoutburst. The resulting constraint on the Shakura-Sunyaev parameter, alpha_{hot} ~ 0.1, is consistent with the value inferred from the fast dwarf nova decays. By looking at the slow decay rate for superoutbursts, which occur in systems below the period gap, in combination with the slow decay rate in one long outburst above the period gap (in U Gem), we infer a steep dependence of the decay rate on orbital period for long outbursts. This implies a steep dependence of alpha_{cold} on orbital period, consistent with tidal torquing as being the dominant angular momentum transport mechanism in quiescent disks in interacting binary systems.

Effects of a 3-Hour Sleep Delay on Sleep Homeostasis in Alcohol Dependent Adults

This study evaluated slow wave activity homeostatic response to a mild sleep challenge in alcohol-dependent adults compared to healthy controls. Participants maintained a 23:00-06:00 schedule for 5 days verified by actigraphy and diary, followed by 3 nights in the lab: adaptation, baseline, and a sleep delay night with an 02:00-09:00 schedule. Sleep ' Chronophysiology laboratory. 48 alcohol-dependent adults (39 men, 9 women) who were abstinent for at least 3 weeks and 16 healthy control adults (13 men, 3 women), 21-55 years of age participated in study. N/A. Slow wave EEG activity (SWA) in consecutive NREM periods was compared between baseline and sleep delay nights and between AD and HC groups, using age and sex as statistical covariates. The AD group showed a blunted SWA response to sleep delay with significantly lower SWA power than the HC group. Exponential regression analyses confirmed lower asymptotic SWA with a slower decay rate over NREM sleep time in the AD group. Results were similar for raw SWA and %SWA on the delay night expressed relative to baseline SWA. Alcohol dependence is associated with impaired SWA regulation and a blunted response to a mild homeostatic sleep challenge.

Mood disorders in the light of genes, comorbidity and contemporary treatment

The Author(s) 2011. This article is published with open access at Springerlink.com Affective disorders like depression rank worldwide among the most disabling in terms of WHO global burden of disease, are socioeconomically relevant, severe and prevalent. Due to persisting cognitive symptoms, these diseases lead to enormous social disabilities and they dramatically increase the risk of suicide. A genetic influence and the serotonin transporter (5HTT) play a major role in the pathophysiology of mood disorders and suicidal behavior. Pinto et al. [1] investigated the effect of genomic imprinting of the four 5HTT genetic markers and expression of 5HTT alleles in lymphocytes of suicide attempters and 312 nuclear families with at least one member affected by bipolar disorder. Allele 2651T was transmitted more often to bipolar patients, but the authors did not find differential gene expression between bipolar suicide attempters and non-attempters, which does not support a role for allelic expression of 5HTT in suicidal behavior. Due to the high risk of suicide and social disabilities despite antidepressant medication, add-on therapy entailing fewer side effects should be investigated. Tajalizadekhoob et al. [2] applied fish oil capsules containing polyunsaturated fatty acids (PUFAs) in elderly patients with mild to moderate depression as add-on therapy during a period of six months. Treatment with PUFAs showed significant effects compared to placebo and may be beneficial in depressed elderly patients who are at greater risk for cardiovascular diseases. In fact, major depression is associated with increased volumes of visceral fat and high prevalence of the metabolic syndrome, leading to coronary artery disease. Greggersen et al. [3] investigated visceral fat content in young depressed women with and without comorbid borderline personality disorder. They found a significant increase in visceral fat content in major depression, but no additional effects of borderline personality disorder, which does not seem to be an additive risk factor for the metabolic syndrome. Sleep disturbances are common in both depressed and alcohol-dependent patients, including decreased slow wave sleeps (SWS). Brower et al. [4] compared power spectral analysis of polysomnography recordings in men with alcohol dependence compared to subjects with major depression. Both groups showed blunted slow wave activities: men with major depression showed the least slow wave activities in the first non-REM period, whereas men with alcohol dependence had the slowest slow wave activity decay rate. New treatment approaches should selectively improve these different components of sleep homeostasis. In a study by Cordes et al. [5], antidepressant therapy with clomipramine has shown to induce a significant increase in serum prolactin levels in women, but not in men with major depression, indicating effects of clomipramine on the central monoaminergic system. In line with a glutamate hypothesis of depression, the N-methyl-Daspartate (NMDA) receptor antagonist ketamine has been shown to be therapeutically effective in unipolar and bipolar depression. In a retrospective chart analysis of Kranaster et al. [6], effects of ketamine as anesthetic during electroconvulsive therapy (ECT) in patients with therapyresistant depression have been compared to anesthesia with the barbiturate thiopental. Interestingly, the ketamine group

Formation and size distribution of pores in poly(ɛ-caprolactone) foams prepared by pressure quenching using supercritical CO 2

Many biomaterial-based regenerative therapies require foam structures, which temporarily mimic the extracellular matrix. The pore structure of these scaffolds needs to be tailored to the specific requirements of the clinical application. Poly(ɛ-caprolactone) (PCL) is a semi-crystalline, aliphatic polyester, which is applied as degradable implant material. In this paper we explored how thermodynamic and kinetic conditions in a supercritical CO 2 (scCO 2) supported foaming process influence the final morphology of the foam. With help of a view cell, we have systematically investigated the foaming with scCO 2 in the pressure range from 78 to 200 bar at temperatures between 25 and 50 °C. Foams were obtained both above the pressure dependent melting temperature ( T m) but also below this temperature, i.e. from supercooled melt states. Foams were characterized by μCT X-ray computed tomography and scanning electron microscopy. The pore size distributions of the obtained foams show characteristic properties (widths, maxima) depending on the initial thermodynamic state of the CO 2/PCL system before pressure quenching, the rate of the pressure decay, and the thermal history of the system. We try to rationalize the dependency of foam morphology and quench conditions with thermodynamic model calculations. The initial amount of CO 2 in the PCL melt was calculated with the Sanchez-Lacombe equation of state. Pressure quenching with a slow pressure decay rate is considered an isothermal process where for a fast rate an adiabatic process is assumed. Both processes differ in their phase separation mechanism. It turned out that the CO 2-induced melting point depression of the semi-crystalline polymer is an important factor. The variation of foaming conditions allows the preparation of scaffolds with specific morphological parameters (mean pore size, pore distribution, and pore connectivity).

Comparing the Kinetics of NK Cells, CD4, and CD8 T Cells in Murine Cytomegalovirus Infection

NK cells recognize virus-infected cells with germline-encoded activating and inhibitory receptors that do not undergo genetic recombination or mutation. Accordingly, NK cells are often considered part of the innate immune response. The innate response comprises rapid early defenders that do not form immune memory. However, there is increasing evidence that experienced NK cells provide increased protection to secondary infection, a hallmark of the adaptive response. In this study, we compare the dynamics of the innate and adaptive immune responses by examining the kinetic profiles of the NK and T cell response to murine CMV infection. We find that, unexpectedly, the kinetics of NK cell proliferation is neither earlier nor faster than the CD4 or CD8 T cell response. Furthermore, early NK cell contraction after the peak of the response is slower than that of T cells. Finally, unlike T cells, experienced NK cells do not experience biphasic decay after the response peak, a trait associated with memory formation. Rather, NK cell contraction is continuous, constant, and returns to below endogenous preinfection levels. This indicates that the reason why Ag-experienced NK cells remain detectable for a prolonged period after adoptive transfer and infection is in part due to the high precursor frequency, slow decay rate, and low background levels of Ly49H(+) NK cells in recipient DAP12-deficient mice. Thus, the quantitative contribution of Ag-experienced NK cells in an endogenous secondary response, with higher background levels of Ly49H(+) NK cells, may be not be as robust as the secondary response observed in T cells.

Modeling of magnetic material displaying magnetic aftereffect with slow decay rates

For magnetic materials that display slow decay rates, the entire relaxation process cannot be observed experimentally within a reasonable time interval. While magnetic aftereffect behavior has been understood and analyzed quantitatively in general, the important parameters of magnetic materials with slow decay cannot be easily extracted. We present comprehensive experimental characterization of time, field, and temperature dependence of magnetic properties of a magnetic nanocomposite, which exhibits slow decay. Based on the measurement results and previously developed Preisach–Arrhenius model, we propose an analytical model that can predict the shape of the entire aftereffect curves at different temperatures with only the major hysteresis loop and one aftereffect curve at a specific holding field within the region of interest. The model is validated with both simulated data and measured data. This model allows the derivation of an analytical formula for the time variation of the magnetization based on a Gaussian distribution.

Reduction of Noise From MR Thermometry Measurements During HIFU Characterization Procedures

Magnetic resonance (MR) thermometry is a valuable method for characterizing thermal fields generated by high intensity focused ultrasound (HIFU) transducers in tissue phantoms and excised tissues. However, infiltration of noise signals generated by external rf sources into the scanner orifice limits the ability of the scanner to measure temperature rise during the heating or ablation phase. In this study, magnetic resonance interferometry (MRI) monitored HIFU ablations are performed on freshly excised porcine liver samples, at varying sonication times, 20 s, 30 s, and 40 s at a constant acoustic intensity level of 1244 W/cm2. Temperature throughout the procedure was measured using proton resonant frequency MR thermometry. Without filtering, reliable temperature measurements during the heating phase could not be obtained since temperature maps appeared blurred and analysis was impossible. Also, measurements acquired during the cooling phase decayed manifested an unrealistically slow rate of temperature decay. This abnormally slow rate was confirmed with computational results. A low-pass RC filter circuit was subsequently incorporated into the experimental setup to prevent infiltration of noise signals in the MRI orifice. This modified RC filter circuit allowed noninvasive measurement of the HIFU induced temperature rise during the heating phase followed by temperature decay during cooling. The measured data were within 13% agreement with the temperature rise computed by solving the acoustic and heat equations.

Long memory in a linear stochastic Volterra differential equation

In this paper we consider a linear stochastic Volterra equation which has a stationary solution. We show that when the kernel of the fundamental solution is regularly varying at infinity with a log-convex tail integral, then the autocovariance function of the stationary solution is also regularly varying at infinity and its exact pointwise rate of decay can be determined. Moreover, it can be shown that this stationary process has either long memory in the sense that the autocovariance function is not integrable over the reals or is subexponential. Under certain conditions upon the kernel, even arbitrarily slow decay rates of the autocovariance function can be achieved. Analogous results are obtained for the corresponding discrete equation.

Contribution of major lipophilic antioxidants to the antioxidant activity of basil extracts: an EPR study

The present research analyses the contribution of some lipid antioxidants to the antioxidant activity of lipophilic extracts from basil by an electron paramagnetic resonance (EPR) study using the stable free radical 1,1-diphenyl-2-picrylhydrazyl (DPPH). DPPH assay is considered an easy and accurate method with regard to measuring the antioxidant activity of plant extracts and EPR has already been employed to determine antioxidant activities of lipophilic plant extracts. Lipid extracts were obtained from basil grown hydroponically for 20 or 35 days from sowing and in soil for 35 days from sowing. Fast and slow rate constants were distinguishable in the decay kinetics of DPPH mixture added with lipid extract. Antioxidants with kinetics characterized by a fast decay rate were tocopherols and chlorophylls, whereas those characterized by a slow decay rate were carotenoids, among which were β-carotene, lutein, β-apo-8'-carotenal and zeaxanthin. The 20-day hydroponically grown sample, which showed higher contents of tocopherol, chlorophyll and carotenoid molecules, was the sample endowed with the higher content of fast lipophilic antioxidants (FLA) and slow lipophilic antioxidants (SLA). The three samples showed different compositions of FLA and SLA, giving rise to different decay kinetics. Despite the differences, in all samples tocopherol contributed about 0.3% to the bulk of FLA, whereas the figure for chlorophyll was about 40%, evidencing the relevant but little-studied role of chlorophyll as an antioxidant.

Temporal variability of deadwood volume and quality in boreal old-growth forests

Reference deadwood volumes from natural forests for forest management and restoration are often derived from one-time measurements or from repeated measurements over short time-scales. Such an approach often assumes an equilibrium state between tree mortality and decomposition, which is questionable in many boreal forest ecosystems due to the occurrence of allogenic disturbances. Using a simulation model based on empirical estimates of tree mortality, disturbance chronologies and models of wood decay class dynamics, this study aimed at characterizing variability in the volume and quality of deadwood for the past 200 years. The variability of deadwood volumes in old-growth forests, arising from differences in disturbance regimes and differing decay rates, was exemplified in two areas of Picea abies-dominated forests in northern Europe. The results imply that with stable deadwood input and slow decay rates the deadwood volume may be in an equilibrium state. On the contrary, if moderate-severity disturbances occur such a state seems improbable. Both study areas displayed continuity in deadwood availability, although temporary paucity in the early decay classes with shortest residence times was also observed. The results stress the importance of understanding the dynamic nature of deadwood in old-growth forests, instead of the traditional view of deadwood as a static ecosystem component.

Patients on HAART often have an excess of unintegrated HIV DNA: Implications for monitoring reservoirs

HIV establishes a latent reservoir early in infection that is resistant to anti-retroviral therapy and has a slow rate of decay. It is thought that the majority of HIV DNA in treated patients is integrated since unintegrated HIV DNA appears to be unstable. Thus, to monitor the HIV latent reservoir, total HIV DNA is commonly measured in PBMC from infected individuals. We investigated how often total approaches integrated HIV DNA in treated patients. To do this, we first assessed how accurate our integration assay is and determined the error in our measurements of total and integrated HIV DNA. We demonstrated an excess of total over integrated HIV DNA was present in a subset of patients, suggesting that measurements of total HIV DNA do not always correlate to the level of integration. Determining the cause of this excess and its frequency may have important implications for understanding HIV latent reservoir maintenance.

Enhanced Synaptic Inhibition Disrupts the Efferent Code of Cerebellar Purkinje Neurons in Leaner Cav2.1 Ca2+ Channel Mutant Mice

Cerebellar Purkinje cells (PCs) encode afferent information in the rate and temporal structure of their spike trains. Both spontaneous firing in these neurons and its modulation by synaptic inputs depend on Ca(2+) current carried by Ca(v)2.1 (P/Q) type channels. Previous studies have described how loss-of-function Ca(v)2.1 mutations affect intrinsic excitability and excitatory transmission in PCs. This study examines the effects of the leaner mutation on fast GABAergic transmission and its modulation of spontaneous firing in PCs. The leaner mutation enhances spontaneous synaptic inhibition of PCs, leading to transitory reductions in PC firing rate and increased spike rate variability. Enhanced inhibition is paralleled by an increase in the frequency and amplitude of spontaneous inhibitory postsynaptic currents (sIPSCs) measured under voltage clamp. These differences are abolished by tetrodotoxin, implicating effects of the mutation on spike-induced GABA release. Elevated sIPSC frequency in leaner PCs is not accompanied by increased mean firing rate in molecular layer interneurons, but IPSCs evoked in PCs by direct stimulation of these neurons exhibit larger amplitude, slower decay rate, and a higher burst probability compared to wild-type PCs. Ca(2+) release from internal stores appears to be required for enhanced inhibition since differences in sIPSC frequency and amplitude in leaner and wild-type PCs are abolished by thapsigargin, an ER Ca(2+) pump inhibitor. These findings represent the first account of the functional consequences of a loss-of-function P/Q channel mutation on PC firing properties through altered GABAergic transmission. Gain in synaptic inhibition shown here would compromise the fidelity of information coding in these neurons and may contribute to impaired cerebellar function resulting from loss-of function mutations in the Ca(V)2.1 channel gene.

Renormalization Group Maps for Ising Models in Lattice-Gas Variables

Real space renormalization group maps, e.g., the majority rule transformation, map Ising type models to Ising type models on a coarser lattice. We show that each coefficient of the renormalized Hamiltonian in the lattice gas variables depends on only a finite number of values of the renormalized Hamiltonian. We introduce a method which computes the values of the renormalized Hamiltonian with high accuracy and so computes the coefficients in the lattice gas variables with high accuracy. For the critical nearest neighbor Ising model on the square lattice with the majority rule transformation, we compute over 1,000 different coefficients in the lattice gas variable representation of the renormalized Hamiltonian and study the decay of these coefficients. We find that they decay exponentially in some sense but with a slow decay rate. We also show that the coefficients in the spin variables are sensitive to the truncation method used to compute them.

Stochastic signaling in biochemical cascades and genetic systems in genetically engineered living cells

Living cells, either prokaryote or eukaryote, can be integrated within whole-cell biochips (WCBCs) for various applications. We investigate WCBCs where information is extracted from the cells via a cascade of biochemical reactions that involve gene expression. The overall biological signal is weak due to small sample volume, low intrinsic cell response, and extrinsic signal loss mechanisms. The low signal-to-noise ratio problem is aggravated during initial detection stages and limits the minimum detectable signal or, alternatively, the minimum detection time. Taking into account the stochastic nature of biochemical process, we find that the signal is accompanied by relatively large noise disturbances. In this work, we use genetically engineered microbe sensors as a model to study the biochips output signal stochastic behavior. In our model, the microbes are designed to express detectable reporter proteins under external induction. We present analytical approximated expressions and numerical simulations evaluating the fluctuations of the synthesized reporter proteins population based on a set of equations modeling a cascade of biochemical and genetic reactions. We assume that the reporter proteins decay more slowly than messenger RNA molecules. We calculate the relation between the noise of the input signal (extrinsic noise) and biochemical reaction statistics (intrinsic noise). We discuss in further details two cases: (1) a cascade with large decay rates of all biochemical reactions compared to the protein decay rate. We show that in this case, the noise amplitude has a positive linear correlation with the number of stages in the cascade. (2) A cascade which includes a stable enzymatic-binding reaction with slow decay rate. We show that in this case, the noise strongly depends on the protein decay rate. Finally, a general observation is presented stating that the noise in whole-cell biochip sensors is determined mainly by the first reactions in the genetic system with weak dependence on the number of stages in the cascade.

Formation of nanoscale spatially indirect excitons: Evolution of the type-II optical character of CdTe/CdSe heteronanocrystals

In this work, the evolution of the optical properties of nanoscale spatially indirect excitons as a function of the size, shape, and composition of the heteronanostructure is investigated, using colloidal CdTe/CdSe heteronanocrystals (2.6 nm diameter CdTe core and increasing CdSe volume fraction) as a model system. Emphasis is given to quantitative aspects such as the absorption cross section of the lowest-energy exciton transition $({\ensuremath{\mu}}_{SS})$, Stokes shift, linewidths, and the exciton radiative lifetime. The hole wave function remains confined to the CdTe core while the electron wave function is initially delocalized over the whole heteronanocrystal ($type\text{\ensuremath{-}}{I}^{1/2}$ regime), and gradually localizes in the CdSe segment as the growth proceeds, until the spatially indirect exciton transition becomes the lowest-energy transition (type-II regime). This results in a progressive shift of the optical transitions to lower energies, accompanied by a decrease in the oscillator strengths at emission energies and an increase in the exciton radiative lifetimes. The onset of the type-II regime is characterized by the loss of structure of the lowest-energy absorption band, accompanied by a simultaneous increase in the Stokes shift values and transition linewidths. This can be understood by considering the dispersion of the hole and electron states in $k$ space. The ${\ensuremath{\mu}}_{SS}$ values decrease rapidly in the ${\text{type-I}}^{1/2}$ regime but only slightly in the type-II regime. This shows that the indirect exciton formation leads primarily to redistribution of the oscillator strength of the lowest-energy transition over a wider frequency range. The total absorption cross section per ion-pair unit (i.e., integrated over all the exciton transitions) remains essentially constant during the heteronanocrystal growth, demonstrating that ${\ensuremath{\mu}}_{SS}$ is redistributed from higher-energy transitions of both the CdTe and the CdSe segments, in response to the reduction in the electron-hole wave-function overlap. Two radiative decay rates are observed and ascribed to exciton states with different degrees of localization of the electron wave function (an upper state with a faster decay rate and a lower state with a slower decay rate). The results presented here provide fundamental insights into nanoscale spatially indirect exciton transitions, highlighting the crucial role of a number of parameters (viz., electron-hole spatial correlation, exciton dispersion and exciton degeneracy, shape effects, and electronic coupling).

Stress-Induced Hsp70 Gene Expression and Inactivation of Cryptosporidium parvum Oocysts by Chlorine-Based Oxidants

Our research on the mechanisms of action of chlorine-based oxidants on Cryptosporidium parvum oocysts in water revealed a dual-phase effect: (i) response to oxidative stress, which was demonstrated by induced expression of the Hsp70 heat shock gene, and (ii) oocyst inactivation as a result of long-term exposure to oxidants. The relative biocidal effects of sodium hypochlorite (bleach) and electrolytically generated mixed oxidant solution (MOS) on C. parvum oocysts were compared at identical free chlorine concentrations. Oocyst inactivation was determined by quantitative reverse transcription-PCR (qRT-PCR) amplification of the heat-induced Hsp70 mRNA and compared with tissue culture infectivity. According to both assays, within the range between 25 and 250 mg/liter free chlorine and with 4 h contact time, MOS exhibits a higher efficacy in oocyst inactivation than hypochlorite. Other RNA-based viability assays, aimed at monitoring the levels of beta-tubulin mRNA and 18S rRNA, showed relatively slow decay rates of these molecules following disinfection by chlorine-based oxidants, rendering these molecular diagnostic viability markers inappropriate for disinfection efficacy assessment.