The microscopic nature of localization in the quantum Hall effect.

The quantum Hall effect arises from the interplay between localized and extended states that form when electrons, confined to two dimensions, are subject to a perpendicular magnetic field. The effect involves exact quantization of all the electronic transport properties owing to particle localization. In the conventional theory of the quantum Hall effect, strong-field localization is associated with a single-particle drift motion of electrons along contours of constant disorder potential.

Scattering of bunched fractionally charged quasiparticles.

We report the unexpected bunching of Laughlin's quasiparticles, induced by an extremely weak backscattering potential at exceptionally low electron temperatures (T<10 mK), deduced from shot noise measurements. Backscattered charges q=nue, specifically, q=e/3, q=2e/5, and q<3e/7, in the respective filling factors, were measured. For the same settings but at a slightly higher electron temperature, the measured backscattered charges were q=e/3, q=e/5, and q=e/7, as expected.

Bone marrow as a priming site for T-cell responses to blood-borne antigen.

Although bone marrow is known as a primary lymphoid organ, its potential to serve as a secondary immune organ has hardly been explored. Here we demonstrate that naive, antigen-specific T cells home to bone marrow, where they can be primed. Antigen presentation to T cells in bone marrow is mediated via resident CD11c+ dendritic cells.

Spin and polarized current from Coulomb blockaded quantum dots.

We report measurements of spin transitions for GaAs quantum dots in the Coulomb blockade regime and compare ground and excited state transport spectroscopy to direct measurements of the spin polarization of emitted current. Transport spectroscopy reveals both spin-increasing and spin-decreasing transitions, as well as higher-spin ground states, and allows g factors to be measured down to a single electron. The spin of emitted current in the Coulomb blockade regime, measured using spin-sensitive electron focusing, is found to be polarized along the direction of the applied magnetic field regardless of the ground state spin transition.

Efficient engraftment of human primary breast cancer transplants in nonconditioned NOD/Scid mice.

We describe a new human tumor xenotransplant animal model that is highly efficient for engraftment, does not need host conditioning and is suitable for in vivo studies of human tumors. Pieces of 61 freshly operated primary breast tumors were implanted into 172 irradiated and 228 nonconditioned NOD/Scid mice. A high mortality was observed in irradiated but not in nonconditioned recipients.

Highly efficient transport of carboxyfluorescein diacetate succinimidyl ester into COS7 cells using human papillomavirus-like particles.

Human papillomavirus virus-like particles (VLPs) have recently been used to deliver genes into mammalian cells in vitro and in vivo. Here, we investigated whether VLPs may serve as an efficient carrier of low molecular weight compounds (e.g.

A gate-controlled bidirectional spin filter using quantum coherence.

We demonstrate a quantum coherent electron spin filter by directly measuring the spin polarization of emitted current. The spin filter consists of an open quantum dot in an in-plane magnetic field; the in-plane field gives the two spin directions different Fermi wavelengths resulting in spin-dependent quantum interference of transport through the device. The gate voltage is used to select the preferentially transmitted spin, thus setting the polarity of the filter.

Influence of adjuvant hormone therapy and chemotherapy on the immune system analysed in the bone marrow of patients with breast cancer.

Purpose: Bone marrow is a special compartment for antitumor immunological memory in patients with breastcancer. Until now, the influence of adjuvant systemic therapy on the immune system has only been investigated in peripheral blood and not in bone marrow. In this study, we analyzed the effect of hormone therapy and chemotherapy on the immune activation status in bone marrow.

Detecting spin-polarized currents in ballistic nanostructures.

We demonstrate a mesoscopic spin polarizer/analyzer system that allows the spin polarization of current from a quantum point contact in a large in-plane magnetic field to be measured. A transverse electron focusing geometry is used to couple current from an emitter point contact into a collector point contact. At large in-plane fields, with the point contacts biased to transmit only a single spin (g View Article and Find Full Text PDF

Zero-resistance states induced by electromagnetic-wave excitation in GaAs/AlGaAs heterostructures.

The observation of vanishing electrical resistance in condensed matter has led to the discovery of new phenomena such as, for example, superconductivity, where a zero-resistance state can be detected in a metal below a transition temperature T(c) (ref. 1). More recently, quantum Hall effects were discovered from investigations of zero-resistance states at low temperatures and high magnetic fields in two-dimensional electron systems (2DESs).

T cell memory, anergy and immunotherapy in breast cancer.

T cell immunity in breast cancer is suggested to play a role in tumor dormancy, a period of stability which can correspond to the time interval between primary treatment and tumor recurrence. Bone marrow in breast cancer patients seems to be particularly important because it is highly enriched with cancer specific memory T cells. Similar cells can be found in peripheral blood, but these appear to be functionally anergic.

Cognate interactions between memory T cells and tumor antigen-presenting dendritic cells from bone marrow of breast cancer patients: bidirectional cell stimulation, survival and antitumor activity in vivo.

Dendritic cells (DC) and T cells were generated from Ficoll separated bone marrow (BM) mononuclear cells of primary operated breast cancer patients according to new cell culture protocols. BM-DC were capable of functioning as professional antigen-presenting cells (APCs) and of inducing autologous antigen-specific memory T-cell responses to either tetanus toxoid recall antigen or to breast cancer antigens. Treatment with lipopolysaccharide (LPS) resulted in phenotypic and functional maturation of BM-DC.

Long-range spatial correlations in the exciton energy distribution in GaAs/AlGaAs quantum wells.

Variations in the width of a quantum well (QW) are known to be a source of broadening of the exciton line. Using low temperature near-field optical microscopy, we have exploited the dependence of exciton energy on well width to show that in GaAs QWs, these seemingly random well-width fluctuations actually exhibit well-defined order-strong long-range correlations appearing laterally, in the plane of the QW, as well as vertically, between QWs grown one on top of the other. We show that these fluctuations are correlated with the commonly found mound structure on the surface.

Low-temperature fate of the 0.7 structure in a point contact: a Kondo-like correlated state in an open system.

Besides the usual conductance plateaus at multiples of 2e(2)/h, quantum point contacts typically show an extra plateau at approximately 0.7(2e(2)/h), believed to arise from electron-electron interactions that prohibit the two spin channels from being simultaneously occupied. We present evidence that the disappearance of the 0.

Bunching of fractionally charged quasiparticles tunnelling through high-potential barriers.

Shot noise measurements have been used to measure the charge of quasiparticles in the fractional quantum Hall (FQH) regime. To induce shot noise in an otherwise noiseless current of quasiparticles, a barrier is placed in its path to cause weak backscattering. The measured shot noise is proportional to the charge of the quasiparticles; for example, at filling factor v=1/3, noise corresponding to q=e/3 appears.

Superantigen reactive Vbeta6+ T cells induce perforin/granzyme B mediated caspase-independent apoptosis in tumour cells.

The endogenous viral superantigen 7 in DBA/2 mice serves as a target antigen on syngeneic ESb-MP lymphoma cells for allogeneic graft-vs-leukaemia reactive cells. Allogeneic viral superantigen 7 reactive Vbeta6+ T cells are able to transfer graft-vs-leukaemia reactivity and to kill specifically viral superantigen 7+ ESb-MP tumour cells in vitro. Here we elucidate the mechanism of this superantigen specific cell lysis.

Internal transitions of negatively charged magnetoexcitons and many body effects in a two-dimensional electron gas.

Internal transitions of quasi-two-dimensional, negatively charged magnetoexcitons ( X-) and their evolution with excess electron density have been studied in GaAs/AlGaAs quantum wells. In the dilute electron limit, due to magnetic translational invariance, the optically detected resonance spectra are dominated by bound-to-continuum bands in contrast to the negatively charged donor system D-, which exhibits strictly bound-to-bound transitions. With increasing excess electron density Landau-level filling factors nu<2 the X--like transitions are blueshifted; they are absent for nu>2.

Generation of dendritic cells from human bone marrow mononuclear cells: advantages for clinical application in comparison to peripheral blood monocyte derived cells.

Dendritic cells (DCs) currently used for vaccination in clinical studies to induce immunity against malignant cells are normally generated from peripheral blood-derived monocytes. Here we studied conditions for the generation of DCs from unseparated human bone marrow (BM) mononuclear cells and compared them functionally with DCs from blood. The two types of DCs, from bone marrow (BM-DC) and peripheral blood (BL-DC), were generated in parallel from the same normal healthy donors by culturing in serum-free X-VIVO 20 medium containing GM-CSF and IL-4, and then the phenotypes and functions were compared.

Nitric oxide-induced apoptosis in tumor cells.

Nitric oxide (NO), an important molecule involved in neurotransmission, vascular homeostasis, immune regulation, and host defense, is generated from a guanido nitrogen of L-arginine by the family of NO synthase enzymes. Large amounts of NO produced for relatively long periods of time (days to weeks) by inducible NO synthase in macrophages and vascular endothelial cells after challenge with lipopolysaccharide or cytokines (such as interferons, tumor necrosis factor-alpha, and interleukin-1), are cytotoxic for various pathogens and tumor cells. This cytotoxic effect against tumor cells was found to be associated with apoptosis (programmed cell death).

Inhibition of nitric-oxide-mediated apoptosis in Jurkat leukemia cells despite cytochrome c release.

We have recently shown that nitric-oxide (NO)-induced apoptosis in Jurkat human leukemia cells requires degradation of mitochondria phospholipid cardiolipin, cytochrome c release, and activation of caspase-9 and caspase-3. Moreover, an inhibitor of lipid peroxidation, Trolox, suppressed apoptosis in Jurkat cells induced by NO donor glycerol trinitrate. Here we demonstrate that this antiapoptotic effect of Trolox occurred despite massive release of the mitochondrial protein cytochrome c into the cytosol and mitochondrial damage.

Therapy of human tumors in NOD/SCID mice with patient-derived reactivated memory T cells from bone marrow.

In an analysis of 84 primary-operated breast cancer patients and 11 healthy donors, we found that the bone marrow of most patients contained memory T cells with specificity for tumor-associated antigens. Patients' bone marrow and peripheral blood contained CD8+ T cells that specifically bound HLA/peptide tetramers. In short-term culture with autologous dendritic cells pre-pulsed with tumor lysates, patients' memory T cells from bone marrow (but not peripheral blood) could be specifically reactivated to interferon-gamma-producing and cytotoxic effector cells.

Enrichment of memory T cells and other profound immunological changes in the bone marrow from untreated breast cancer patients.

Previous studies with animal tumors showed that bone marrow (BM) is a privileged site where potentially lethal tumor cells are controlled in a dormant state by the immune system. Here, we investigated BM of breast cancer patients with respect to tumor cell content, immune activation status and memory T-cell content. BM-derived cells from primary operated breast cancer patients (n = 90) were compared with those from healthy donors (n = 10) and also with cells from respective blood samples.

Evidence of Hofstadter's Fractal Energy Spectrum in the Quantized Hall Conductance.

The energy spectrum of a two-dimensional electron system in a perpendicular homogeneous magnetic field and a weak lateral superlattice potential with square symmetry is composed of Landau bands with recursive internal subband structure. The Hall conductance in the minigaps is anticipated to be quantized in integer multiples of e(2)/h that vary erratically from minigap to minigap in accordance with a Diophantine equation. Hall measurements on samples with the requisite properties uncover this long searched for evidence of Hofstadter's butterflylike energy spectrum.

Dissection of tumor and host cells from metastasized organs for testing gene expression directly ex vivo.

The interaction between tumor and host cells determines to a large extent the outcome, namely tumor growth and progression toward metastases or tumor arrest, dormancy, or rejection. Most of the studies published so far on interactions of tumor cells and host cells were made in vitro and dealt with aspects such as cell adhesion, proliferation, invasiveness, cytotoxicity, or cytokine production. As the microenvironment in tissue culture differs in many respects from that in vivo, new approaches for in vivo studies of tumor-host cell interactions is of utmost importance in cancer research.