Time, momentum, and energy resolved pump-probe tunneling spectroscopy of two-dimensional electron systems

Real-time probing of electrons can uncover intricate relaxation mechanisms and many-body interactions in strongly correlated materials. Here, we introduce time, momentum, and energy resolved pump-probe tunneling spectroscopy (Tr-MERTS). The method allows the injection of electrons at a particular energy and observation of their subsequent decay in energy-momentum space. Using Tr-MERTS, we visualize electronic decay processes, with lifetimes from tens of nanoseconds to tens of microseconds, in Landau levels formed in a GaAs quantum well. Although most observed features agree with simple energy-relaxation, we discovered a splitting in the nonequilibrium energy spectrum in the vicinity of a ferromagnetic state. An exact diagonalization study suggests that the splitting arises from a maximally spin-polarized state with higher energy than a conventional equilibrium skyrmion. Furthermore, we observe time-dependent relaxation of the splitting, which we attribute to single-flipped spins forming skyrmions. These results establish Tr-MERTS as a powerful tool for studying the properties of a 2DES beyond equilibrium.

The Impact of Rubella Virus Infection on a Secondary Inflammatory Response in Polarized Human Macrophages

Macrophages (MΦ) are known to exhibit distinct responses to viral and bacterial infection, but how they react when exposed to the pathogens in succession is less well understood. Accordingly, we determined the effect of a rubella virus (RV)-induced infection followed by an LPS-induced challenge on cytokine production, signal transduction and metabolic pathways in human GM (M1-like)- and M (M2-like)-MΦ. We found that infection of both subsets with RV resulted in a low TNF-α and a high interferon (IFN, type I and type III) release whereby M-MΦ produced far more IFNs than GM-MΦ. Thus, TNF-α production in contrast to IFN production is not a dominant feature of RV infection in these cells. Upon addition of LPS to RV-infected MΦ compared to the addition of LPS to the uninfected cells the TNF-α response only slightly increased, whereas the IFN-response of both subtypes was greatly enhanced. The subset specific cytokine expression pattern remained unchanged under these assay conditions. The priming effect of RV was also observed when replacing RV by IFN-β one putative priming stimulus induced by RV. Small amounts of IFN-β were sufficient for phosphorylation of Stat1 and to induce IFN-production in response to LPS. Analysis of signal transduction pathways activated by successive exposure of MΦ to RV and LPS revealed an increased phosphorylation of NFκB (M-MΦ), but different to uninfected MΦ a reduced phosphorylation of ERK1/2 (both subtypes). Furthermore, metabolic pathways were affected; the LPS-induced increase in glycolysis was dampened in both subtypes after RV infection. In conclusion, we show that RV infection and exogenously added IFN-β can prime MΦ to produce high amounts of IFNs in response to LPS and that changes in glycolysis and signal transduction are associated with the priming effect. These findings will help to understand to what extent MΦ defense to viral infection is modulated by a following exposure to a bacterial infection.

Enhancement of Parametric Effects in Polariton Waveguides Induced by Dipolar Interactions

Exciton-polaritons are hybrid light-matter excitations arising from the nonperturbative coupling of a photonic mode and an excitonic resonance. Behaving as interacting photons, they show optical third-order nonlinearities providing effects such as optical parametric oscillation or amplification. It has been suggested that polariton-polariton interactions can be greatly enhanced by inducing aligned electric dipoles in their excitonic part. However, direct evidence of a true particle-particle interaction, such as superfluidity or parametric scattering, is still missing. In this Letter, we demonstrate that dipolar interactions can be used to enhance parametric effects such as self-phase modulation in waveguide polaritons. By quantifying these optical nonlinearities, we provide a reliable experimental measurement of the direct dipolar enhancement of polariton-polariton interactions.

Acoustoelectric Study of Microwave-Induced Current Domains

Surface acoustic waves (SAW) have been utilized to investigate the properties of a two-dimensional electron system subjected to a perpendicular magnetic field and monochromatic microwave radiation in the regime where the so-called microwave-induced zero-resistance states form. Contrary to conventional magnetotransport in Hall bar and van der Pauw geometries, the collimated SAW beam probes only the bulk of the electronic system exposed to this wave. Clear signatures appear in the SAW propagation velocity, corroborating that neither contacts nor sample edges are a root source for their emergence. By virtue of the directional nature of this probing method and with the assistance of theoretical modeling, we were able to demonstrate that the SAW response depends on the angle between its propagation vector and the orientation of domains that spontaneously form when zero-resistance is observed in transport. This confirms in unprecedented manner the formation of an inhomogeneous phase under these nonequilibrium conditions.

Chiral Modes at Exceptional Points in Exciton-Polariton Quantum Fluids

We demonstrate the generation of chiral modes-vortex flows with fixed handedness in exciton-polariton quantum fluids. The chiral modes arise in the vicinity of exceptional points (non-Hermitian spectral degeneracies) in an optically induced resonator for exciton polaritons. In particular, a vortex is generated by driving two dipole modes of the non-Hermitian ring resonator into degeneracy. Transition through the exceptional point in the space of the system's parameters is enabled by precise manipulation of real and imaginary parts of the closed-wall potential forming the resonator. As the system is driven to the vicinity of the exceptional point, we observe the formation of a vortex state with a fixed orbital angular momentum (topological charge). This method can be extended to generate higher-order orbital angular momentum states through coalescence of multiple non-Hermitian spectral degeneracies. Our Letter demonstrates the possibility of exploiting nontrivial and counterintuitive properties of waves near exceptional points in macroscopic quantum systems.

The colored Hanbury Brown-Twiss effect

The Hanbury Brown-Twiss effect is one of the celebrated phenomenologies of modern physics that accommodates equally well classical (interferences of waves) and quantum (correlations between indistinguishable particles) interpretations. The effect was discovered in the late thirties with a basic observation of Hanbury Brown that radio-pulses from two distinct antennas generate signals on the oscilloscope that wiggle similarly to the naked eye. When Hanbury Brown and his mathematician colleague Twiss took the obvious step to propose bringing the effect in the optical range, they met with considerable opposition as single-photon interferences were deemed impossible. The Hanbury Brown-Twiss effect is nowadays universally accepted and, being so fundamental, embodies many subtleties of our understanding of the wave/particle dual nature of light. Thanks to a novel experimental technique, we report here a generalized version of the Hanbury Brown-Twiss effect to include the frequency of the detected light, or, from the particle point of view, the energy of the detected photons. Our source of light is a polariton condensate, that allows high-resolution filtering of a spectrally broad source with a high degree of coherence. In addition to the known tendencies of indistinguishable photons to arrive together on the detector, we find that photons of different colors present the opposite characteristic of avoiding each others. We postulate that fermions can be similarly brought to exhibit positive (boson-like) correlations by frequency filtering.

Das 2q37-Deletionssyndrom

Durch Deletionen im chromosomalen Bereich 2q37 wird ein klinisches Bild verursacht, das als „Albright-hereditäre-Osteodystrophie(AHO)-ähnliches Syndrom“ bezeichnet wird. Aufgrund der Hauptmerkmale leichte bis mäßig schwere Entwicklungsverzögerung, Verhaltensauffälligkeiten und Brachydakytlie Typ E wird dieser Phänotyp auch Brachydaktylie-mentales-Retardierungs-Syndrom (BDMR, MIM 600430) genannt. Durch Eingrenzung minimaler krankheitsrelevanter 2q37-Deletionsintervalle wurde das Histondeacetylase-4-Gen (HDAC4, MIM 605314), ein zentraler Transkriptionsrepressor, der in der Gehirn-, Muskel- und Skelettentwicklung involviert ist, als krankheitsrelevantes Gen für das BDMR-Syndrom identifiziert. Bislang wurden intragenische HDAC4-Mutationen bei 2 Patienten mit BDMR-Syndrom nachgewiesen, bei denen zunächst aufgrund von Verhaltensauffälligkeiten klinisch ein Smith-Magenis-Syndrom vermutet worden war. Untersuchungen mittels Array-CGH („comparative genomic hybridization“) decken ein breiteres phänotypisches Spektrum des 2q37-Deletionssyndroms als bislang bekannt auf. So war der Nachweis einer 2q37-Deletion auch bei entwicklungsverzögerten Patienten ohne BDE möglich.

Direct measurement of exciton-exciton interaction energy

We report a direct measurement of the spectral function (real and imaginary self-energy) of excitons with a repulsive interaction potential. These results allow a stringent test of many-body theories of the exciton-exciton interaction which is independent of the exciton density calibration.

Current-induced anisotropy and reordering of the electron liquid-crystal phases in a two-dimensional electron system

The correlated phases in a two-dimensional electron system with a high index partially filled Landau level are studied in transport under nonequilibrium conditions by imposing a dc-current drive. At filling 1/4 and 3/4 of these Landau levels, where the charge density wave picture predicts an isotropic bubble phase, the dc drive induces anisotropic transport behavior consistent with stripe order. The easy axis of the emerging anisotropic phase is perpendicular to the drive. At half filling the anisotropic stripe phase is stabilized by the dc drive provided drive and easy-axis directions coincide.

Considerations on equilibration of two-dimensional excitons in coupled quantum well structures

In this paper we discuss the issues of the equilibration dynamics of spatially indirect two-dimensional excitons in a coupled quantum well structure, in particular those trapped by an in-plane harmonic potential trap. We discuss the relative timescales for several processes. In the experiments with an in-plane trap, we can use the size of the exciton cloud as a measure of the temperature of particles. At low lattice temperatures the exciton temperature is higher than that of the lattice, even long after equilibrium has obviously been reached. We discuss the effects that can be responsible for this.

Bose-Einstein Condensation of Microcavity Polaritons in a Trap

We have created polaritons in a harmonic potential trap analogous to atoms in optical traps. The trap can be loaded by creating polaritons 50 micrometers from its center that are allowed to drift into the trap. When the density of polaritons exceeds a critical threshold, we observe a number of signatures of Bose-Einstein condensation: spectral and spatial narrowing, a peak at zero momentum in the momentum distribution, first-order coherence, and spontaneous linear polarization of the light emission. The polaritons, which are eigenstates of the light-matter system in a microcavity, remain in the strong coupling regime while going through this dynamical phase transition.

Trapping excitons in a two-dimensional in-plane harmonic potential: experimental evidence for equilibration of indirect excitons

We have trapped a gas of long-lifetime, high-mobility excitons in an in-plane harmonic potential. Trapping is an important step toward the goal of a controlled Bose-Einstein condensate of excitons. We show that the repulsive interaction between the excitons plays a dominant role in the behavior of the excitons, in contrast with the weak interactions in atomic gases. We show that under proper conditions the excitons thermalize in the trap to a well-defined equilibrium spatial distribution.

Circular-polarization-dependent study of the microwave photoconductivity in a two-dimensional electron system

The polarization dependence of the low field microwave photoconductivity and absorption of a two-dimensional electron system has been investigated in a quasioptical setup in which linear and any circular polarization can be produced in situ. The microwave induced resistance oscillations and the zero resistance regions are notably immune to the sense of circular polarization. This observation is discrepant with a number of proposed theories. Deviations between different polarizations occur only near the cyclotron resonance where an unprecedented large resistance response is observed.

Long-distance diffusion of excitons in double quantum well structures

In this Letter we report on lateral diffusion measurements of excitons at low temperature in double quantum wells of various widths. The structure is designed so that excitons live up to 30 micros and diffuse up to 500 microm. Particular attention is given to establishing that the transport occurs by exciton motion. The deduced exciton diffusion coefficients have a very strong well width dependence, and obey the same power law as the diffusion coefficient for electrons.

Prenatal diagnosis and molecular cytogenetic characterization of an unusual complex structural rearrangement in a pregnancy following intracytoplasmic sperm injection (ICSI)

We report on a balanced complex chromosomal aberration detected in a fetus after amniocentesis. The pregnancy was achieved after intracytoplasmic sperm injection. GTG-banding revealed a complex structurally rearranged karyotype with a translocation between chromosomes 5 and 15 and an additional paracentric inversion in the der(15) between bands 5q11.2 and 5q15. Ag-NOR staining showed an interstitial active nuclear organizer region in the der(15). Molecular cytogenetic analyses using whole-chromosome-painting probes, comparative genomic hybridization, and multicolor banding did not point to further structural aberrations or imbalances. Therefore, a complex rearrangement with three breakpoints has occurred, and the karyotype can be described as 46,XX,der(5)t(5;15) (q11.2;p12),der(15)t(5;15)(q11.2;p12)inv(5)(q11.2q15).

[Pathophysiological and therapeutic aspects of amniotic fluid embolism (anaphylactoid syndrome of pregnancy): case report with lethal outcome and overview]

A 35-years old gravida IV and para II underwent caesarean section because of fetal distress following induction of labour. During operation the patient developed disseminated intravascular coagulation (DIC), severe haemorrhage and shock necessitating massive blood transfusion,hysterectomy with pelvic packing, and high-dose catecholamines. Ultimately, recombinant factor VIIa was given to control bleeding. During the first 24 hours after operation, both clinical and laboratory findings showed that the severe DIC was on the course to recovery.However, the patient subsequently developed multiple organ dysfunction syndrome with respiratory and renal failure requiring mechanical ventilation and haemodialysis.All therapeutical efforts could not help that the patient passed away due to an inevitable multiple organ failure on the 12th day after the operation. Given the constellation of diagnostic and clinical findings, the most likely diagnosis was amniotic fluid embolism (AFE), a rare complication of pregnancy. The following differential diagnoses were less likely or excluded in this reported patient: pre-eclampsia/pregnancy-induced hypertension,HELLP syndrome,anaphylaxis,uterine rupture, transfusion reactions,pulmonary embolism. AFE occurs rarely, and because studies in animal models cannot reproduce accurately the pathophysiological and clinical alterations seen in humans, its pathogenesis remains unclear. It has been proposed that the clinical syndrome of AFE occurs when fetal antigens pass the maternal immunological barrier in susceptible mothers. The recognition of fetal antigens by maternal immune system subsequently triggers the release of endogenous mediators that are responsible for dramatic pathophysiological disturbances.Furthermore, the components of amniotic fluid initiate the DIC. These events are more consistent with septic shock and anaphylactic shock than with an embolic process and it was proposed that the term "amniotic fluid embolism" be changed to "anaphylactoid syndrome of pregnancy". At present, no therapy has been found to consistently improve outcomes in women with AFE.Patients who survive the initial insult are at high risk for multiple organ failure. The mortality of AFE remains high.

Long-range transport in excitonic dark states in coupled quantum wells

During the past ten years, coupled quantum wells have emerged as a promising system for experiments on Bose condensation of excitons, with numerous theoretical and experimental studies aimed at the demonstration of this effect. One of the issues driving these studies is the possibility of long-range coherent transport of excitons. Excitons in quantum wells typically diffuse only a few micrometres from the spot where they are generated by a laser pulse; their diffusion is limited by their lifetime (typically a few nanoseconds) and by scattering due to disorder in the well structure. Here we report photoluminescence measurements of InGaAs quantum wells and the observation of an effect by which luminescence from excitons appears hundreds of micrometres away from the laser excitation spot. This luminescence appears as a ring around the laser spot; almost none appears in the region between the laser spot and the ring. This implies that the excitons must travel in a dark state until they reach some critical distance, at which they collectively revert to luminescing states. It is unclear whether this effect is related to macroscopic coherence caused by Bose condensation of excitons.

Influence of molecular structure on sorption of phenoxyalkanoic herbicides on soil and its particle size fractions

The sorption and desorption behaviors of four phenoxyalkanoic acid herbicides and their metabolites on four agricultural soils and soil particle size fractions were examined. Generally, there was a trend of increasing adsorption and decreasing desorption in the order mecoprop < MCPA < dichlorprop < 2,4-D. The significant increase in adsorption of the phenolic metabolites can be explained by their lower polarity and enhanced partition in the organic soil matrix. Estimation of sorption distribution coefficients from particle size fraction adsorption data was possible for a sandy soil and a silty Cambisol soil only. It is suggested that increasing steric demand, for example, molecular volume, and slight changes in the polarity of the compounds affect their adsorption properties. Comparison of adsorption and desorption data of structurally similar compounds obtained from a variety of soils allows investigation of structure-induced differences in sorption strength.

Automated computer-assisted evaluation of diagnosis-and-procedure-reports in Austrian hospitals

Austria's 320 hospitals with 73,000 beds have to transmit a minimum basic data set for each hospital stay with diagnosis and procedures as well as scores for use in intensive care units (last only in performance-oriented financed hospitals). Based on these data, 160 hospitals or 53,000 beds are financed through performance oriented flat rates per case (LDFs--Leistungsorientierte Diagnosen-Fallpauschalen). Those LDFs are in some principles similar to DRG's (diagnosis related groups), but have been developed by the Federal Ministry of Labor, Health and Social Affairs (BMAGS). 1.94 million data sets of hospital stays, which were reported for financing in the year 1997 had to be analyzed for their correctness and plausibility. For this aim the "Scoringprogramm" of the BMAGS is in use. We describe in detail how many diagnoses and procedures are automatically checked with diagnosis, sex, age, length of stay etc. 1.6% warnings resulted from this checking, and no errors have been reported. The checking routines have to be further developed. At present data seem to be used only with caution for epidemiology or for analyzing medical quality. For financing purposes it might be reliable, especially if data quality commissions are enlarged and if evaluation of data with medical records is improved.

gamma delta+ T cells regulate major histocompatibility complex class II(IA and IE)-dependent susceptibility to coxsackievirus B3-induced autoimmune myocarditis

Coxsackievirus B3 (CVB3) infection induces myocardial inflammation and myocyte necrosis in some, but not all, strains of mice. C57BL/6 mice, which inherently lack major histocompatibility complex (MHC) class II IE antigen, develop minimal cardiac lesions despite high levels of virus in the heart. The present experiments evaluate the relative roles of class II IA and IE expression on myocarditis susceptibility in four transgenic C57BL/6 mouse strains differing in MHC class II antigen expression. Animals lacking MHC class II IE antigen (C57BL/6 [IA+ IE-] and ABo [IA- IE-]) developed minimal cardiac lesions subsequent to infection despite high concentrations of virus in the heart. In contrast, strains expressing IE (ABo Ealpha [IA- IE+] and Bl.Tg.Ealpha [IA+ IE+]) had substantial cardiac injury. Myocarditis susceptibility correlated to a Th1 (gamma interferon-positive) cell response in the spleen, while disease resistance correlated to a preferential Th2 (interleukin-4-positive) phenotype. Vgamma/Vdelta analysis indicates that distinct subpopulations of gamma delta+ T cells are activated after CVB3 infection of C57BL/6 and Bl.Tg.Ealpha mice. Depletion of gamma delta+ T cells abrogated myocarditis susceptibility in IE+ animals and resulted in a Th1-->Th2 phenotype shift. These studies indicate that the MHC class II antigen haplotype controls myocarditis susceptibility, that this control is most likely mediated through the type of gamma delta T cells activated during CVB3 infection, and finally that different subpopulations of gamma delta+ T cells may either promote or inhibit Th1 cell responses.

Plasma levels of glutathione, alpha-tocopherol and lipid peroxides in polytraumatized patients; evidence for a stimulating effect of TNF alpha on glutathione synthesis

Prognosis and outcome of polytraumatized patients are determined by the possible development of multiple organ failure (MOF). Among the direct traumatic organ damage, it is caused by a systemic inflammatory reaction. This might be triggered by an activation of the inflammatory mediator cascade following hemorrhagic-traumatic shock as well as by oxygen-derived free radicals (ROS). The aim of our present study was to answer the following questions: 1. Is the "oxidative stress" measurable during the development of MOF after polytraumatic injury? 2. Is there a relation between the activation of the inflammatory mediator cascade and changes of the organism's antioxidative system? The study group included 26 patients (15 survivors, 11 non-survivors) suffering from severe polytraumatic injury (Hannover Polytrauma Score 12-63 points). Plasma levels of reduced (GSH) and oxidized (GSSG) glutathione alpha-tocopherol (TOC), lipid peroxides (expressed in terms of thiobarbituric acid reagible substances = TBARS), and tumor necrosis factor alpha (TNF) were measured each day from the point of admission on the ICU until the discharge or death of the patients. The following results were obtained: Independent from the outcome, we observed a continuous loss of plasma sulfhydryl groups and TOC. In the patients developing a MOF score > 5 on 10th day after injury (n = 6), a significant increase in plasma GSSG level was measurable. Additionally, a total loss of plasma GSH was seen in some of these patients indicating the collapse of the GSH-dependent antioxidative system. Similar changes were never observed in patients with MOF score < or = 5 on 10th day after injury (n = 15). In this group, a significant correlation between plasma TNF peaks and short time GSH boosts was obtained as a possible indicative for a stimulating effect of TNF on GSH synthesis. It can be concluded that processes of oxidative stress in connection with a consumption of endogenic antioxidants might be able to promote the development of MOF after polytraumatic injury.

Decreased N-acetyl-aspartate/choline ratio and increased lactate in the frontal lobe of patients with Huntington's disease: a proton magnetic resonance spectroscopy study

BACKGROUND

Both the effect of the mutation and the pathogenesis of Huntington's disease are unknown and a lack of biological markers for the natural history of the disease impedes the evaluation of novel therapeutic approaches.

METHODS

Proton magnetic resonance spectroscopy was carried out on a frontal region of the cortex in 17 patients with clinically overt Huntington's disease and four asymptomatic gene carriers.

RESULTS

Eight of 17 (47%) clinically affected patients with Huntington's disease and each of the asymptomatic carriers had lactate peaks in the frontal cortex which were not present in controls. The N-acetyl-aspartate/choline (NAA/Ch) ratio was significantly reduced in the symptomatic patients indicating the presence of neuronal loss. The reduction was related to the clinical severity of the disease and was absent in the asymptomatic carriers.

CONCLUSION

The finding of lactate peaks supports the hypothesis that disturbed cerebral energy metabolism contributes to the pathogenesis of Huntington's disease.

[New knowledge of the etiology and pathogenesis of Huntington chorea]

Huntington's disease (HD) is a neurodegenerative disorder for which no causal therapy is currently available. It is inherited as an autosomal dominant trait and the responsible gene was localized 10 years ago to chromosome 4. Recently the gene has been identified. This discovery now allows a definitive diagnosis to be made in most cases. Preclinical testing, however, requires careful psychological counselling. So far the structure and function of the gene product are unknown. Using experimental neurotoxicological methods it is possible to mimic several features of the disease process to such an extent that preliminary hypotheses regarding the function of the encoded protein are possible. It will be of great interest to see how the results of molecular genetic studies and of experimental research can be synthesized in the future.

The Kabuki (Niikawa-Kuroki) syndrome: further delineation of the phenotype in 29 non-Japanese patients

The Kabuki (Niikawa-Kuroki) syndrome was reported in 1981 by Niikawa et al. and Kuroki et al. in a total of ten unrelated Japanese children with a characteristic array of multiple congenital anomalies and mental retardation. The syndrome is characterized by a distinct face, mild to moderate mental retardation, postnatal growth retardation, dermatoglyphic and skeletal abnormalities. In Japan, the syndrome appears to have an incidence of about 1:32,000 newborns. Outside of Japan, a growing number of patients have been recognized. Clinical data are presented on 29 Caucasian patients; the patients were diagnosed over a relatively short period of time, indicating that the incidence outside of Japan is probably not lower than in Japan. A literature review of 89 patients (60 Japanese and 29 non-Japanese) is given. In 66% of the non-Japanese patients serious neurological problems were present, most notably hypotonia and feeding problems (which were not only related to the cleft palate); this was not reported in the Japanese patients. Inheritance is not clear. Most patients are isolated, sex-ratio is equal. The syndrome can be recognized in patients with cleft (lip/)palate, with mild to moderate developmental delay and in young children with hypotonia and/or feeding problems. In counselling parents, the designation "Kabuki" syndrome seems to be more appropriate than "Kabuki make-up" syndrome.

[Clinico-genetic diagnosis of ataxia telangiectatica (Louis-Bar syndrome)]

We describe the possible difficulties in getting the diagnosis "ataxia telangiectasia" using the example of a 16 years old girl. If cases of cerebellar ataxia in childhood present without classical symptoms, the diagnosis of ataxia telangiectasia should not be excluded before chromosome analysis. In our case, first signs of cerebellar ataxia were observed from the age of 11 years and we found only mild, atypical located and late onset telangiectasis. Other signs of the syndrome, such as elevated alpha-fetoproteine and deficiency of IgA or IgE could not be detected. Chromosome analysis, however, demonstrated a breakage syndrome with chromosome 14 to 7 translocation and established a firm diagnosis of ataxia telangiectasia. Patients with chromosome breakage syndromes including the Louis-Bar-syndrome have an increased risk for malignomas. Therefore chromosome analysis should be undertaken in cases of children with cerebellar ataxia, and frequent radiological examination avoided.

Picosecond pump and probe spectroscopy utilizing freely propagating terahertz radiation

We demonstrate the feasibility of scaling up a terahertz-pulse generation scheme for use with a 10-Hz amplified femtosecond laser system. Visible pulsed excitation combined with a far-infrared probe should prove to be a powerful picosecond time-resolved technique.

[Alpha 1-fetoprotein--a marker of potential PUVA side-effects in psoriasis?]

Serum concentrations of alpha 1-fetoprotein (AFP) during PUVA treatment have been analyzed in 12 patients suffering from severe psoriasis or psoriatic arthritis. The results have been compared with AFP levels in psoriatics without PUVA treatment (group II), patients with psoriatic arthritis treated with methotrexate (group III), as well as dermatological patients without psoriasis (group IV). All groups revealed AFP levels below 25 ng/ml. Although a slight raise of AFP could be observed during PUVA therapy (p less than 0.005), we assume that AFP detection cannot be regarded as a marker of potential PUVA side-effects in psoriasis.

Direct analysis of lead in fruit juice by anodic stripping voltammetry with no prior sample preparation

A method is presented for determining lead in fruit juice in less than 3 min after instrument calibration. The range examined is 0.01 to 1.3 ppm lead. The method is compared with 3 other methods in general use. Standard error of estimates between the methods compared range from 0.023 to 0.051 ppm for a set of 50 samples and from 0.037 to 0.091 ppm for a set of 9 samples. Regression correlation coefficients between methods range from 0.968 to 0.995. Judged by the comparisons, the direct method is precise and accurate over greater than a 100-fold range of lead concentrations.