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Biomedical subjects

J S Brooks

Publications and source records attributed to J S Brooks.

At least 19 recordsLinked to original sources
PubMed2006

Vortex dynamics and the Fulde-Ferrell-Larkin-Ovchinnikov state in a magnetic-field-induced organic superconductor.

Under special conditions, a superconducting state where the order parameter oscillates in real space, the so-called FFLO state, is theoretically predicted to exist near the upper critical field, as first proposed by Fulde and Ferrell, and Larkin and Ovchinnikov. We report systematic measurements of the interlayer resistance in high magnetic fields to 45 T in the two-dimensional magnetic-field-induced organic superconductor lambda-(BETS)2FeCl4, where BETS is bis(ethylenedithio)tetraselenafulvalene. The resistance is found to show characteristic dip structures in the superconducting state. The results are consistent with pinning interactions between the vortices penetrating the insulating layers and the order parameter of the FFLO state. This gives strong evidence for an oscillating order parameter in real space.

Journal Article↗
PubMed2005

Resonant nernst effect in the metallic and field-induced spin density wave States of (TMTSF)2ClO4.

We examine an unusual phenomenon where, in tilted magnetic fields near magic angles parallel to crystallographic planes, a "giant" resonant Nernst signal has been observed by Wu et al. [Phys. Rev. Lett. 91, 056601 (2003)] in the metallic state of an organic conducting Bechgaard salt. We show that this effect appears to be a general feature of these materials and is also present in the field-induced spin density wave phase with even larger amplitude. Our results place conditions on any model that treats the metallic state as a state with finite Cooper pairing.

Journal Article↗
PubMed2005

Quantum oscillation of Hall resistance in the extreme quantum limit of an organic conductor (TMTSF)2ClO4.

We report resistance and magnetic torque experiments under a high magnetic field up to 45 T in a three dimensional quantum Hall (QH) system (TMTSF)(2)ClO(4), where TMTSF = tetramethyltetraselenafulvalene. The Hall resistance shows huge oscillations accompanied with sign reversal after the final QH state, where the Landau level filling factor is unity, is removed above 26 T. The magnetic torque also oscillates with the field. The results suggest that a novel quantum state, where the character of the carriers periodically changes with the field, is stabilized in the extreme quantum limit.

Journal Article↗
PubMed2004

High magnetic field induced charge density wave state in a quasi-one-dimensional organic conductor.

The quasi-one-dimensional organic conductor (Per)2Pt(mnt)2 exhibits a charge density wave ground state below 8 K. Magnetoresistance and magnetization measurements show that the charge density wave is suppressed with magnetic fields of order 20 T, above which a high resistance state, with a cascade of subphases, appears. This new state, tentatively identified as a field induced charge density wave, reenters a low resistance state above 40 T. The results are presented in light of theoretical work [D. Zanchi et al. Phys. Rev. B 53, 1240 (1996)]] involving field induced charge density wave ground states in high magnetic fields.

Journal Article↗
PubMed2002

Three-dimensional fermi-liquid ground state in the quasi-one-dimensional cuprate PrBa(2)Cu(4)O(8).

The interchain resistivity of PrBa(2)Cu(4)O(8) has been measured in high magnetic fields up to 30 T. Co-herent interchain transport at low temperatures is destroyed by a large magnetic field applied perpendicular to the CuO chains. Comparisons with quasiclassical transport theory provide strong experimental support for a three-dimensional Fermi-liquid ground state in PrBa(2)Cu(4)O(8), despite extreme anisotropy in its electronic properties and the presence of strong electron correlations.

Journal Article↗
PubMed2001

MCM2 is an independent predictor of survival in patients with non-small-cell lung cancer.

PURPOSE: Minichromosome maintenance protein 2 (MCM2) is a component of the prereplicative complex. It is essential for eukaryotic DNA replication and is only expressed in proliferating cells. The prognostic utility of MCM2 compared with Ki-67, another marker of proliferating cells, on survival of patients with non-small-cell lung cancer (NSCLC) was studied. PATIENTS AND METHODS: We examined the immunohistochemical expression of MCM2 and Ki-67 in primary pathologic tumor specimens from 221 NSCLC patients. For each marker, the fraction of tumor cells with positive staining was assessed as a percentage and categorized into four groups: 0% to 24%, 25% to 49%, 50% to 74%, and > or = 75%. MCM2 and Ki-67 immunoreactivities were compared with each other, and associations with pathologic and clinical parameters predictive of survival were analyzed with the chi(2) test. Cox regression models were used to assess associations between MCM2 and Ki-67 and survival while controlling for confounders. RESULTS: Independent variables significantly associated with survival were tumor stage, performance status, and staining category. Patients with less than 25% MCM2 immunoreactivity had a longer median survival time than patients with > or = 25% MCM2 immunoreactivity (46 v 31 months; P =.039) and a lower relative risk (RR) of death (RR, 0.55, 95% confidence interval, 0.34 to 0.88). There was no significant association between survival and Ki-67 expression. CONCLUSION: Immunostaining of tumor cells for MCM2 is an independent prognostic parameter of survival for patients with NSCLC. Interpretable results can be obtained on more than 96% of paraffin-embedded specimens, and approximately 35% will be in the favorable subgroup, with less than 25% positively stained tumor cells. Whether MCM2 is predictive of response to therapy needs to be studied.

Adenocarcinoma↗
PubMed2001

Superconductivity in an organic insulator at very high magnetic fields.

We investigate by electrical transport the field-induced superconducting state (FISC) in the organic conductor lambda-(BETS)2FeCl4. Below 4 K, antiferromagnetic-insulator, metallic, and eventually superconducting (FISC) ground states are observed with increasing in-plane magnetic field. The FISC state survives between 18 and 41 T and can be interpreted in terms of the Jaccarino-Peter effect, where the external magnetic field compensates the exchange field of aligned Fe3+ ions. We further argue that the Fe3+ moments are essential to stabilize the resulting singlet, two-dimensional superconducting state.

Journal Article↗
PubMed2001

MCM2--a promising marker for premalignant lesions of the lung: a cohort study.

BACKGROUND: Because cells progressing to cancer must proliferate, marker proteins specific to proliferating cells may permit detection of premalignant lesions. Here we compared the sensitivities of a classic proliferation marker, Ki-67, with a new proliferation marker, MCM2, in 41 bronchial biopsy specimens representing normal mucosa, metaplasia, dysplasia, and carcinoma in situ. METHODS: Parallel sections were stained with antibodies against MCM2 and Ki-67, and the frequencies of staining were independently measured by two investigators. Differences were evaluated statistically using the two-sided correlated samples t-test and Wilcoxon rank sum test. RESULTS: For each of the 41 specimens, the average frequency of staining by anti-MCM2 (39%) was significantly (p < 0.001) greater than by anti-Ki-67 (16%). In metaplastic lesions anti-MCM2 frequently detected cells near the epithelial surface, while anti-Ki-67 did not. CONCLUSIONS: We conclude that MCM2 is detectable in 2-3 times more proliferating premalignant lung cells than is Ki-67. The promise of MCM2 as a sensitive marker for premalignant lung cells is enhanced by the fact that it is present in cells at the surface of metaplastic lung lesions, which are more likely to be exfoliated into sputum. Future studies will determine if use of anti-MCM2 makes possible sufficiently early detection to significantly enhance lung cancer survival rates.

Biomarkers, Tumor↗
PubMed2001

Quantum melting of the quasi-two-dimensional vortex lattice in kappa- (ET)2Cu(NCS)(2).

We report torque magnetization measurements in regions of the mixed state phase diagram ( B approximately mu(o)H(c2) and T(c)/10(3)) of the organic superconductor kappa-(ET)2Cu(NCS)(2), where quantum fluctuations are expected to dominate thermal effects. Over most of the field range below the irreversibility line ( B(irr)), magnetothermal instabilities are observed in the form of flux jumps. The abrupt cessation of these instabilities just below B(irr) indicates a quantum melting transition from a quasi-two-dimensional vortex lattice phase to a quantum liquid phase.

Journal Article↗
PubMed2001

Field-induced dynamic diamagnetism in a charge-density-wave system.

ac susceptibility measurements of the charge-density-wave (CDW) compound alpha-(BEDT-TTF)(2)-KHg(SCN)(4) at magnetic fields, mu0H >23 T, above its Pauli paramagnetic limit, reveal unambiguously that the magnetic hysteresis observed previously within this CDW phase is diamagnetic and can only be explained by induced currents. It is argued that the ensemble of experimental techniques amounts to a strong case for dissipationless conductivity within this phase.

Journal Article↗
PubMed2001

Field-induced metal-insulator transition in a two-dimensional organic superconductor.

The quasi-two-dimensional organic superconductor beta"-(BEDT-TTF)2SF5CH2CF2SO3 (Tc approximately 4.4 K) shows very strong Shubnikov-de Haas (SdH) oscillations which are superimposed on a highly anomalous steady background magnetoresistance, Rb. Comparison with de Haas-van Alphen oscillations allows a reliable estimate of Rb which is crucial for the correct extraction of the SdH signal. At low temperatures and high magnetic fields insulating behavior evolves. The magnetoresistance data violate Kohler's rule, i.e., cannot be described within the framework of semiclassical transport theory, but converge onto a universal curve appropriate for dynamical scaling at a metal-insulator transition.

Journal Article↗
PubMed1999

Photofrin photodynamic therapy for treatment of AIDS-related cutaneous Kaposi's sarcoma.

OBJECTIVE: Kaposi's sarcoma, the most common malignancy in AIDS patients, often presents with painful cutaneous lesions that are difficult to treat effectively despite a wide variety of therapeutic approaches. We used photodynamic therapy in an attempt to provide effective palliative treatment for this disease. METHODS: Photodynamic therapy utilizes the activation by light of a photosensitizing drug that preferentially accumulates in tumor tissue such as Kaposi's sarcoma. We enrolled 25 patients who received 1.0 mg/kg of Photofrin 48 h before exposure to 100-400 J/cm2 of 630 nm light. RESULTS: Of the 348 lesions treated, 289 were evaluable: 32.5% had complete clinical response, 63.3% had partial clinical response and 4.2% were clinical failures. There was a strong correlation between response and light dose: 54% of lesions achieved a complete clinical response at optimum light dose (> 250 J/cm2). There was no correlation of response with CD4 cell count nor was there a change in CD4 cell count post-treatment. At 400 J/cm2 full field scabbing and necrosis occurred in 90% of the treated fields. Thus, the maximum tolerated dose was determined to be 300 J/cm2. At light doses of 250 J/cm2 and below the toxicities were limited to erythema and edema in the treatment field. Forty-three biopsies were taken 0.5 h to 4 months post-treatment. These showed little change in the B and T cell infiltrates identified. Kaposi's sarcoma cells disappeared post-treatment in certain lesions. CONCLUSION: Photofrin is effective palliative treatment for HIV-associated Kaposi's sarcoma.

Acquired Immunodeficiency Syndrome↗
PubMed1998

HsMCM2/BM28: a novel proliferation marker for human tumors and normal tissues.

HsMCM2/BM28 is a member of the family of minichromosome maintenance (MCM) proteins, which play a critical role in DNA replication by helping to ensure that DNA is replicated once and only once per cell cycle. The association of HsMCM2 with DNA replication suggested to us that it might prove useful as a new marker for cell proliferation. To test this possibility, we employed immunohistochemistry and immunoblotting to study HsMCM2 expression in both normal human tissues and primary human tumors. We found that HsMCM2 was detectable by immunoblotting in 97% of the studied tumors but in only 27% of the corresponding normal tissues. In normal tissues, the immunoblot signal was weaker than in tumors. Immunohistochemistry revealed that in normal tissues HsMCM2 is present only in proliferating cell nuclei. In most cases, tumor cell nuclei produced a stronger HsMCM2 signal than normal proliferating cell nuclei. Comparative studies revealed that antibodies against HsMCM2 stained fewer nuclei than antibodies against proliferating cell nuclear antigen but usually more than antibodies against Ki-67 (another proliferation-related antigen). Thus, the correlations between proliferation and antigenic signal are different for these three proteins. These results indicate that HsMCM2 is, indeed, a novel marker for proliferating cells. Further studies are required to determine whether the fact that HsMCM2 has a different correlation with proliferation and elevated staining intensity in tumor nuclei (compared to nuclei in normal proliferating cells) will permit it to be a more useful diagnostic and prognostic marker than proliferating cell nuclear antigen and Ki-67.

Biomarkers↗
PubMed1998

Metachronous benign solitary fibrous tumours of the pleura (localized "mesotheliomas"): a case report.

Solitary fibrous tumours are uncommon pleural tumours that are not related to mesotheliomas. They are typically benign and pedunculated and may grow to massive sizes. Surgical resection is usually curative. Tumour recurrence and metachronous development of multiple tumours are unusual. In this report a patient was treated for 3 benign solitary fibrous tumours of the pleura over 23 years. The authors hypothesize that this represents multifocal tumorigenesis as opposed to local tumour recurrence. The importance of complete surgical excision and lifelong radiographic follow-up are stressed.

Aged↗
PubMed1997

Round cell liposarcoma with the insertion (12;16)(q13;p11.2p13).

Cytogenetic analysis of a short-term culture from a round cell liposarcoma revealed ins(12;16)(q13;p11.2p13) as a sole abnormality in all metaphase cells studied. This chromosome rearrangement, thus far not described in liposarcomas, leads to recombination of bands 12q13 and 16p11.2 and, thus, seems to be the equivalent of t(12;16)(q13;p11), a translocation that is highly specific for the myxoid type of liposarcoma. Our case represents the fourth fully karyotyped round cell liposarcoma that displays a cytogenetic rearrangement of bands 12q13 and 16p11, thus supporting the concept that round cell liposarcoma is related to myxoid liposarcoma and constitutes its poorly differentiated form. The fact that ins(12;16) was the only detectable chromosome aberration suggests that the presence of secondary cytogenetic aberrations is not a prerequisite for the development of a round cell histology in liposarcoma.

Adult↗