Persistence of magnons in a site-diluted dimerized frustrated antiferromagnet

We present inelastic neutron scattering and thermodynamic measurements characterizing the magnetic excitations in a disordered spin-liquid antiferromagnet with non-magnetic substitution. The parent compound Ba(3)Mn(2)O(8) is a dimerized, quasi-two-dimensional geometrically frustrated quantum disordered antiferromagnet. We substitute this compound with non-magnetic V(5+) for the S=1 Mn(5+) ions, Ba(3)(Mn(1-x)V (x))(2)O(8), and find that the singlet-triplet excitations which dominate the spectrum of the parent compound persist for the full range of substitution examined, up to x=0.3. We also observe additional low-energy magnetic fluctuations which are enhanced at the greatest substitution values.

The new cold neutron chopper spectrometer at the Spallation Neutron Source: design and performance

The design and performance of the new cold neutron chopper spectrometer (CNCS) at the Spallation Neutron Source in Oak Ridge are described. CNCS is a direct-geometry inelastic time-of-flight spectrometer, designed essentially to cover the same energy and momentum transfer ranges as IN5 at ILL, LET at ISIS, DCS at NIST, TOFTOF at FRM-II, AMATERAS at J-PARC, PHAROS at LANSCE, and NEAT at HZB, at similar energy resolution. Measured values of key figures such as neutron flux at sample position and energy resolution are compared between measurements and ray tracing Monte Carlo simulations, and good agreement (better than 20% of absolute numbers) has been achieved. The instrument performs very well in the cold and thermal neutron energy ranges, and promises to become a workhorse for the neutron scattering community for quasielastic and inelastic scattering experiments.

Giant anharmonic phonon scattering in PbTe

Understanding the microscopic processes affecting the bulk thermal conductivity is crucial to develop more efficient thermoelectric materials. PbTe is currently one of the leading thermoelectric materials, largely thanks to its low thermal conductivity. However, the origin of this low thermal conductivity in a simple rocksalt structure has so far been elusive. Using a combination of inelastic neutron scattering measurements and first-principles computations of the phonons, we identify a strong anharmonic coupling between the ferroelectric transverse optic mode and the longitudinal acoustic modes in PbTe. This interaction extends over a large portion of reciprocal space, and directly affects the heat-carrying longitudinal acoustic phonons. The longitudinal acoustic-transverse optic anharmonic coupling is likely to play a central role in explaining the low thermal conductivity of PbTe. The present results provide a microscopic picture of why many good thermoelectric materials are found near a lattice instability of the ferroelectric type.

Slow and static spin correlations in Dy(2 + x)Ti(2 - x)O(7 - δ)

The static and dynamic spin correlations in the spin ices Dy(2.3)Ti(1.7)O(6.85) and Dy(2)Ti(2)O(7) have been studied in polarized neutron diffraction and neutron spin echo experiments. The measurements reveal that, below 100 mK, the magnetic scattering broadens and shifts to higher |Q| upon stuffing the pyrochlore lattice with additional Dy(3+) ions. These observations can be related, by means of reverse Monte Carlo simulation, to the modified distribution of near-neighbour distances and an overall more antiferromagnetic character of the near-neighbour couplings. The dynamic measurements show that the spin correlations are slower in the stuffed system. These results will be discussed and compared to the holmium analogues.

Neutron scattering investigations of the partially ordered pyrochlore Tb(2)Sn(2)O(7)

Neutron scattering measurements have been performed on polycrystalline Tb(2)Sn(2)O(7) at temperatures above and below that of the phase transition, T(N) = 0.87 K, to investigate further the spin dynamics in the magnetically ordered state. In particular, new neutron spin echo results are presented showing a dependence on Q in the dynamics. We show evidence of the coexistence of static ferromagnetism and dynamically fluctuating spins down to 30 mK and we make a comparison of this partially ordered system to the spin liquid Tb(2)Ti(2)O(7).

Magnetic order and crystal field excitations in Er(2)Ru(2)O(7): a neutron scattering study

The magnetic pyrochlore Er(2)Ru(2)O(7) has been studied with neutron scattering and susceptibility measurements down to a base temperature of 270 mK. For the low temperature phase in which the Er sublattice orders, new magnetic Bragg peaks are reported which can be indexed with integer (hkl) for a face centered cubic cell. Inelastic measurements reveal a wealth of crystal field levels of the Er ion and a copious amount of magnetic scattering below 15 meV. The three lowest groups of crystal field levels are at 6.7, 9.1 and 18.5 meV.

Direct observation of a nuclear spin excitation in Ho2Ti2O7

A single nondispersive excitation is observed by means of neutron backscattering, at E_{0}=26.3 microeV in the spin ice Ho2Ti2O7 but not in the isotopically enriched 162Dy2Ti2O7 analogue. The intensity of this excitation is rather small, less, similar0.2% of the elastic intensity. It is clearly observed below 80 K but resolution limited only below approximately 65 K. The application of a magnetic field up to micro_{0}H=4.5 T, at 1.6 K, has no measurable effect on the energy or intensity. This nuclear excitation is believed to perturb the electronic, Ising spin system resulting in the persistent spin dynamics observed in spin ice compounds.

Tracking the effects of rigidity percolation down to the liquid state: relaxational dynamics of binary chalcogen melts

The stochastic dynamics of binary liquids with formula AxB1-x, x=0-0.4 is investigated by neutron spin-echo spectroscopy. These compositions comprise samples of varying chemical connectivity, ranging from twofold-coordinated liquid Se to higher average coordinated As2S3. The parameters giving the temperature dependence of the relaxation patterns show a quasilinear dependence on the average coordination number. The results thus extend the validity of the rigidity concept into the normal liquid state and emphasize the role played by the fine details of atomic bonding on the dynamics at 10 ps-1 ns scales.

Frustrated spin correlations in diluted spin ice Ho(2-x)La(x)Ti(2)O(7)

We have studied the evolution of the structural properties as well as the static and dynamic spin correlations of spin ice Ho(2)Ti(2)O(7), where Ho was partially replaced by non-magnetic La. The crystal structure of diluted samples Ho(2-x)La(x)Ti(2)O(7) was characterized by x-ray and neutron diffraction and by Ho L(III)-edge and Ti K-edge extended x-ray absorption fine structure (EXAFS) measurements. It is found that the pyrochlore structure remains intact until about x = 0.3, but a systematic increase in local disorder with increasing La concentration is observed in the EXAFS data, especially from the Ti K edge. Quasi-elastic neutron scattering and ac susceptibility measurements show that, in x≤0.4 samples at temperatures above macroscopic freezing, the spin-spin correlations are short ranged and dynamic in nature. The main difference with pure spin ice in the dynamics is the appearance of a second, faster, relaxation process.

Neutron spin-echo investigation of slow spin dynamics in kagomé-bilayer frustrated magnets as evidence for phonon assisted relaxation in SrCr9xGa12-9xO19

A neutron spin-echo investigation of the low temperature spin dynamics in two well-characterized kagomé bilayer compounds SrCr9xGa12-9xO19 (x=0.95, SCGO) and Ba2Sn2ZnCr7xGa10-7xO22 (x=0.97, BSZCGO) reveals two novel features. One is the slowing down of the relaxation rate without critical behavior at Tg, where a macroscopic spin-glass-like freezing occurs. The second is, in SCGO at 4 K (approximately Tg)<T<7 K, the relaxation rate activation energy Ea=7+/-0.4 meV, equal to the energy of a phonon mode, pointing out the role of spin-lattice coupling.

Dynamic properties of a diluted pyrochlore cooperative paramagnet (Tb(p)Y(1-p))2Ti2O7

Investigations of the spin dynamics of the geometrically frustrated pyrochlore (Tb(p)Y(1-p))2Ti2O7, using muon spin relaxation and neutron spin echo, as a function of magnetic coverage p, have been carried out. Our major finding is that paramagnetic fluctuations prevail as T-->0 for all values of p, and that they are sensitive to dilution, indicating a cooperative spin motion. However, the percolation threshold pc is not a critical point for the fluctuations. We also find that the low temperature spectral density has a 1/f behavior, and that dilution slows down the spin fluctuations.

Observation of two time scales in the ferromagnetic manganite La1-xCaxMnO3, x approximately 0.3

We report new zero-field muon spin relaxation and neutron spin echo measurements in ferromagnetic (FM) (La,Ca)MnO3 which suggest at least two spatially separated regions possessing very different Mn-ion spin dynamics. One region displays diffusive relaxation, "critical slowing down" near T(C) and an increasing volume fraction below T(C), suggesting overdamped FM spin waves below T(C). The second region possesses more slowly fluctuating spins, a linewidth independent of q, and a decreasing volume fraction below T(C). The estimated length scale for the inhomogeneity is <or=30 A.

[Chronic erosive, therapy-resistant perianal herpes (type II) with herpes proctitis in AIDS]

In an AIDS patient who had repeated successful treatment with acyclovir in his history, erosive herpes perianalis with herpes proctitis appeared, which persisted over several weeks. High-dose intravenous administration on of acyclovir (500-750 mg, 3 x daily, over 7 weeks) did not reveal any beneficial effects: However, almost complete clearing of the lesions occurred within 3 weeks of intravenous administration of Foscarnet (50 mg/kg body wt., 3 x daily). No relapse was seen in a follow-up period of 4 months. HSV type II was isolated by culture from the erosive lesions before treatment, but no virus was found 1 week after application of Foscarnet. The unusual chronic refractory course of a severe HSV type II infection in AIDS suggests the presence of an acyclovir-resistant HSV strain in this case. This is the first observation indicating acyclovir-resistance in the Federal Republic of Germany and a warning against the unlimited use of acyclovir in AIDS patients. Foscarnet may be beneficial in some of these cases.

Long-term therapy of HIV-associated Kaposi's sarcoma with recombinant interferon alpha-2a

Five young male patients with HIV-associated Kaposi's sarcoma (KS) were treated with recombinant interferon alpha 2a (rIFN-alpha-2a) over a period of 2-2.5 years. An IFN dose of 18 x 10(6) IU was given subcutaneously every day during the first 3 months of treatment and then on alternate days. Additional treatment with radiotherapy and laser therapy was given and, in some cases, isolated skin nodules were excised. Within 7 months of initiation of therapy one patient had a complete remission of his tumours, however, tumour progression recurred after the patient discontinued treatment. In another patient the tumour cleared within 9 months of rIFN therapy, and after 52 months he is still free of KS. The condition of a third patient tended to become stabilized during the first 6 months of therapy, but after 60 months there has been a slow progression. The fourth and fifth patients died 25 and 28 months, respectively, after the histological diagnosis of KS and the initiation of treatment. While on therapy with rIFN-alpha-2a, no life-threatening opportunistic infections occurred. The side-effects were mostly well tolerated, and no severe changes in haematological parameters were caused by the therapy.

[Acute primary phase as an indicator of HIV-1 infection. The general symptoms and polymorphic exanthema with mouth mucosal involvement 2 to 6 weeks before seroconversion]

The initial symptoms of an HIV-1 infection were observed in four patients. The following were characteristic for the acute primary phase: (a) initial maculopapular exanthema, especially of the trunk, with occasional transition into a papulovesical appearance; (b) involvement of the oral mucosa, often of aphthous character; and (c) general malaise with fever and lymphadenopathy. The observed cutaneous changes had, on one hand, features of a Coxsackie or mononucleosis exanthema, on the other of secondary syphilis. In three patients seroconversion occurred within 2-6 weeks, the fourth failed to return for follow-up. The listed acute primary symptoms can be used as the earliest indicators of an HIV-1 infection having occurred.

[Congenital telangiectatic erythema (Bloom syndrome)]

"Congenital telangiectatic erythema" (Bloom's syndrome) is very rare; it is linked to a group of hereditary diseases and a common feature is cellular hypersensitivity to a variety of physical or chemical agents. The mode of transmission is autosomal-recessive. Characteristic criteria for Bloom syndrome are: consanguinity of the parents; androtropia; low birth weight, short stature (proportional); and persistent telangiectatic erythema in sun-exposed areas, sometimes with blistering. The syndrome is also associated with a facultative lack of antibodies. Of great importance is the high leukaemia morbidity among individuals with this syndrome; chromosomal aberrations and breakages play a significant role. Histological changes comprise an increase in dilated vessels in the upper dermis and damage and loss of elastic fibers. We give a review of Bloom's syndrome and present a case report.

[Disseminated mucocutaneous Kaposi sarcoma in AIDS. Clinical and therapeutic experiences in 13 patients]

Since 1980 a new epidemic form of disseminated mucocutaneous Kaposi's sarcoma (KS) with a progressive clinical course has been observed in populations at risk. Since 1982, 13 cases of AIDS-associated KS have been seen in our department; all of them were in young homosexual males with circulating HIV antibodies and a reduction in the ratio of T-helper to T-suppressor lymphocytes (0.05-1.3). Following systemic treatment with recombinant alpha A-interferon (rIFN-alpha A) over a period of 6 months (18 million IU/day for 3 months; later 18 million IU/3 X weekly) together with other concomitant measures (superficial X-ray radiation, argon laser radiation, surgical excision of isolated lesions) we registered complete remission of the remaining lesions in 2 cases, progression of the disease in 4 cases, and at least temporary stabilization of the disease in 7 cases. In 4 patients opportunistic infections occurred during rIFN treatment: Pneumocystis carinii pneumonia (PCP) with lethal outcome in 2 cases, atypical mycobacteriosis in 2 cases, and Legionella pneumoniae infection in 1 case. Two additional deaths were registered due to PCP appearing during the post-treatment period. Life-threatening virus infections were not observed during rIFN treatment. Out of 9 patients receiving prophylactic trimethoprim/sulfamethoxazole medication, only 1 developed allergic exanthema as a result of this drug combination. Occasionally, rIFN-induced leukopenia was seen and pronounced thrombocytopenia appeared in 1 patient during treatment. Overall, systemic rIFN therapy was well tolerated; its long-term administration in patients with AIDS-associated mucocutaneous KS seems to be well justified according to these preliminary observations.(ABSTRACT TRUNCATED AT 250 WORDS)

[Chronic urticaria in the dermatology clinic]

In order to clarify the genesis of different forms of urticaria, particular experiences of the Practicing dermatologist are required regarding allergology as well as the equipment of his practice which is of considerable importance. Certain examination methods should, however, be carried out under clinical conditions, as far as special technical instruments, comparison and reproduction of results and allergy exposition are concerned. Special regard has to be paid to the phenomenon of intolerance. Corresponding reactions are being dealt with increasingly. Even clinical treatment only produced few discoveries of allergens. Therefore, steps have to be taken to set up more effective examination techniques.

Radiotherapy of regional epidermoid carcinoma of the lung: a study in fractionation

This paper reports a prospective randomized multicenter trial of two fractionation schemes in the supervoltage radiotherapy of locally inoperable epidermoid lung cancer. This study was stimulated by the need to provide improved and more acceptable treatment methods for patients with this condition, the most common cell type of lung cancer. The majority of such patients are not suitable for resection because of metastasis or because of extensive local disease, even though exploratory thoracotomy may be performed. It was therefore considered important to identify preferred methods of irradiation in this situation which is found in a large proportion of patients with lung cancer.