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Biomedical subjects

R B Mann

Publications and source records attributed to R B Mann.

At least 19 recordsLinked to original sources
PubMed2006

Soliton solutions to the einstein equations in five dimensions.

We present a new class of solutions in odd dimensions to Einstein's equations containing either a positive or a negative cosmological constant. These solutions resemble the even-dimensional Eguchi-Hanson-(anti)-de Sitter [(A)dS] metrics, with the added feature of having Lorentzian signatures. They provide an affirmative answer to the open question as to whether or not there exist solutions with a negative cosmological constant that asymptotically approach AdS5/gamma but have less energy than AdS5/gamma. We present evidence that these solutions are the lowest-energy states within their asymptotic class.

Journal Article↗
PubMed2005

Alice falls into a black hole: entanglement in noninertial frames.

Two observers determine the entanglement between two free bosonic modes by each detecting one of the modes and observing the correlations between their measurements. We show that a state which is maximally entangled in an inertial frame becomes less entangled if the observers are relatively accelerated. This phenomenon, which is a consequence of the Unruh effect, shows that entanglement is an observer-dependent quantity in noninertial frames. In the high acceleration limit, our results can be applied to a nonaccelerated observer falling into a black hole while the accelerated one barely escapes. If the observer escapes with infinite acceleration, the state's distillable entanglement vanishes.

Journal Article↗
PubMed2004

Three-body dynamics in a (1+1) -dimensional relativistic self-gravitating system.

The results of our study of the motion of a three particle, self-gravitating system in general relativistic lineal gravity is presented for an arbitrary ratio of the particle masses. We derive a canonical expression for the Hamiltonian of the system and discuss the numerical solution of the resulting equations of motion. This solution is compared to the corresponding nonrelativistic and post-Newtonian approximation solutions so that the dynamics of the fully relativistic system can be interpreted as a correction to the one-dimensional Newtonian self-gravitating system. We find that the structure of the phase space of each of these systems yields a large variety of interesting dynamics that can be divided into three distinct regions: annulus, pretzel, and chaotic; the first two being regions of quasiperiodicity while the latter is a region of chaos. By changing the relative masses of the three particles we find that the relative sizes of these three phase space regions changes, and that this deformation can be interpreted physically in terms of the gravitational interactions of the particles. Furthermore, we find that many of the interesting characteristics found in the case where all of the particles share the same mass also appear in our more general study. We find that there are additional regions of chaos in the unequal mass system which are not present in the equal mass case. We compare these results to those found in similar systems.

Journal Article↗
PubMed2004

Chaos in an exact relativistic three-body self-gravitating system.

We consider the problem of three-body motion for a relativistic one-dimensional self-gravitating system. After describing the canonical decomposition of the action, we find an exact expression for the three-body Hamiltonian, implicitly determined in terms of the four coordinates and momentum degrees of freedom in the system. Nonrelativistically these degrees of freedom can be rewritten in terms of a single particle moving in a two-dimensional hexagonal well. We find the exact relativistic generalization of this potential, along with its post-Newtonian approximation. We then specialize to the equal-mass case and numerically solve the equations of motion that follow from the Hamiltonian. Working in hexagonal-well coordinates, we obtain orbits in both the hexagonal and three-body representations of the system, and plot the Poincaré sections as a function of the relativistic energy parameter eta. We find two broad categories of periodic and quasiperiodic motions that we refer to as the annulus and pretzel patterns, as well as a set of chaotic motions that appear in the region of phase space between these two types. Despite the high degree of nonlinearity in the relativistic system, we find that the global structure of its phase space remains qualitatively the same as its nonrelativistic counterpart for all values of eta that we could study. However, the relativistic system has a weaker symmetry and so its Poincare section develops an asymmetric distortion that increases with increasing eta. For the post-Newtonian system we find that it experiences a chaotic transition in the interval 0.21<theta<0.26, above which some of the near-integrable regions degenerate into chaos.

Journal Article↗
PubMed2003

Radiative electroweak symmetry breaking revisited.

In the absence of a tree-level scalar-field mass, renormalization-group methods permit the explicit summation of leading-logarithm contributions to all orders of the perturbative series within the effective potential for SU(2)xU(1) electroweak symmetry. This improvement of the effective potential function is seen to reduce residual dependence on the renormalization mass scale. The all-orders summation of leading-logarithm terms involving the dominant three couplings contributing to radiative corrections is suggestive of a potential characterized by a plausible Higgs boson mass of 216 GeV. However, the tree potential's local minimum at phi=0 is restored if QCD is sufficiently strong.

Journal Article↗
PubMed2003

Mass, action, and entropy of Taub-Bolt-de Sitter spacetimes.

We apply a recent proposal for defining conserved mass in asymptotically de Sitter spacetimes to the class of Taub-Bolt-de Sitter spacetimes. We compute the action, entropy, and conserved mass of these spacetimes, and find that in certain instances the mass and entropy can exceed that of pure de Sitter spacetime, in violation of recent suggestive conjectures to the contrary.

Journal Article↗
PubMed2003

Chaos in a relativistic 3-body self-gravitating system.

We consider the 3-body problem in relativistic lineal [i.e., (1+1)-dimensional] gravity and obtain an exact expression for its Hamiltonian and equations of motion. While general-relativistic effects yield more tightly bound orbits of higher frequency compared to their nonrelativistic counterparts, as energy increases we find in the equal-mass case no evidence for either global chaos or a breakdown from regular to chaotic motion, despite the high degree of nonlinearity in the system. We find numerical evidence for mild chaos and a countably infinite class of nonchaotic orbits, yielding a fractal structure in the outer regions of the Poincaré plot.

Journal Article↗
PubMed2002

Statistical mechanics of relativistic one-dimensional self-gravitating systems.

We consider the statistical mechanics of a general relativistic one-dimensional self-gravitating system. The system consists of N particles coupled to lineal gravity and can be considered as a model of N relativistically interacting sheets of uniform mass. The partition function and one-particle distribution functions are computed to leading order in 1/c where c is the speed of light; as c --> infinity results for the nonrelativistic one-dimensional self-gravitating system are recovered. We find that relativistic effects generally cause both position and momentum distribution functions to become more sharply peaked, and that the temperature of a relativistic gas is smaller than its nonrelativistic counterpart at the same fixed energy. We consider the large-N limit of our results and compare this to the nonrelativistic case.

Journal Article↗
PubMed2001

Long-term results of blood and marrow transplantation for Hodgkin's lymphoma.

PURPOSE: To evaluate the long-term outcome after allogeneic (allo) and autologous (auto) blood or marrow transplantation (BMT) in patients with relapsed or refractory Hodgkin's lymphoma (HL). PATIENTS AND METHODS: We analyzed the outcome of 157 consecutive patients with relapsed or refractory HL, who underwent BMT between March 1985 and April 1998. Patients <or= age 55 with HLA-matched siblings were prioritized toward allo BMT. The median age was 28 years (range, 13 to 52 years) for the 53 allo patients and 30.5 years (range, 11 to 62 years) for the 104 auto patients. RESULTS: The median follow-up after BMT for surviving patients was 5.1 years (range, 1 to 13.8 years). For the entire group, the probabilities of event-free survival (EFS) and relapse at 10 years were 26% (95% confidence interval [CI], 18% to 33%) and 58% (95% CI, 48% to 69%), respectively. According to multivariate analysis, disease status before BMT (sensitive relapse if responding to conventional-dose therapy or resistant disease if not) (hazard ratio [HR] = 0.39, P < .0001) and date of BMT (HR = 0.93, P = .004) were independent predictors of EFS, whereas only disease status (HR = 0.35, P < .0001) influenced relapse. There was a trend for probability of relapse in sensitive patients to be less after allo BMT at 34% (range, 8% to 59%) versus 51% (range, 36% to 67%) for the auto patients (HR = 0.51, P = .17). There was a continuing risk of relapse or secondary acute myeloid leukemia (AML)/myelodysplastic syndrome (MDS) for 12 years after auto BMT, whereas there were no cases of secondary AML/MDS or relapses beyond 3 years after allo BMT. CONCLUSION: There seems to be a clinical graft-versus-HL effect associated with allo BMT. Allo BMT for HL also seems to have a lower risk of secondary AML/MDS than auto BMT. Thus, allo BMT warrants continued study in HL.

Adolescent↗
PubMed2001

Primary cutaneous T-cell-rich B-cell lymphoma: clinically distinct from its nodal counterpart?

The cases of two patients with Stage IE primary cutaneous T-cell-rich B-cell lymphoma (TCRBCL) are described. In both, the lesion showed a dense infiltrate by numerous small T lymphocytes with scattered histiocytes and large atypical B-lymphoid cells. Polymerase chain reaction assays demonstrated that the B cells were monoclonal, with immunoglobulin heavy-chain gene rearrangement. No clonal rearrangements of the T-cell receptor gamma gene were observed. Both patients were disease-free at 4 months and at 5 years after therapy, respectively. Although rare, primary cutaneous T-cell-rich B-cell lymphoma appears to have a better prognosis than its nodal counterpart, with or without skin involvement.

Antigens, CD20↗
PubMed2001

Birds disperse ixodid (Acari: Ixodidae) and Borrelia burgdorferi-infected ticks in Canada.

A total of 152 ixodid ticks (Acari: Ixodidae) consisting of nine species was collected from 82 passerine birds (33 species) in 14 locations in Canada from 1996 to 2000. The Lyme disease spirochete Borrelia burgdorferi Johnson, Schmidt, Hyde, Steigerwaldt & Brenner was cultured from the nymph of a blacklegged tick, Ixodes scapularis Say, that had been removed from a common yellowthroat, Geothlypis trichas L., from Bon Portage Island, Nova Scotia. As a result of bird movement, a nymphal I. scapularis removed from a Swainson's thrush, Catharus ustulatus incanus (Godfrey), at Slave Lake, Alberta, during spring migration becomes the new, most western and northern record of this tick species in Canada. Amblyomma longirostre Koch, Amblyomma sabanerae Stoll, and Ixodes baergi Cooley & Kohls are reported for the first time in Canada. Similarly, Amblyomma americanum L., Arnblyomma maculatum Koch, and ixodes muris Bishopp & Smith are reported for the first time on birds in Canada. After removal of an I. muris gravid female from a song sparrow, Melospiza melodia Wilson, at St. Andrews, New Brunswick, eggs were laid, which developed into larvae, and this new tick-host record demonstrates that birds have the potential to start a new tick population. We conclude that passerine birds disperse several species of ixodid ticks in Canada, and during spring migration translocate ticks from the United States, and Central and South America, some of which are infected with B. burgdorferi.

Animals↗
PubMed1999

Heterogeneity of viral IL-6 expression in HHV-8-associated diseases.

In order to characterize the expression of the viral interleukin-6 (vIL-6) homologue in various human herpesvirus 8 (HHV-8)-associated diseases, in situ hybridization and immunohistochemistry were applied to formalin-fixed specimens. These assays showed consistent expression of vIL-6 in primary effusion lymphomas and in a case of human immunodeficiency virus (HIV)-associated lymphadenopathy with a Castleman's disease-like appearance. In contrast, Kaposi's sarcoma specimens showed marked differences among specimens. In a consecutive series of specimens from the Johns Hopkins archives, vIL-6 expression was demonstrated in one of 13 cases. However, among 7 specimens selected from the AIDS Malignancy Bank because of their high levels of the T1.1 lytic transcript and virion production, vIL-6 expression was consistently demonstrated in infiltrating mononuclear cells and occasional spindle-shaped cells. Thus vIL-6 expression in clinical specimens correlates with other measures of the lytic viral cycle. Both assays generally give congruent results and are consistent with the possibility that vIL-6 expression plays a role in the pathogenesis of a variety of HHV-8-associated diseases.

Adult↗
PubMed1999

Disseminated histoplasmosis causing reversible gaze palsy and optic neuropathy.

Subacute disseminated histoplasmosis is an uncommon entity. Typical neuro-ophthalmologic manifestations are usually secondary to histoplasmomas or encephalitis. A 45-year-old man noted blurred vision while receiving empiric antituberculosis therapy for fever and diffuse granulomatous disease of unknown origin. Vertical-gaze palsy, right horizontal-gaze paresis, and mild right optic neuropathy were found on neuro-ophthalmologic examination. Further questioning revealed a history of frequent contact with fighting cocks from South America. Magnetic resonance images were consistent with multiple hemorrhagic infarcts, areas of inflammation, or both, and cerebral angiography showed changes consistent with vasculitis. A previously obtained biopsy specimen from the duodenum was restained and found to be positive for fungal elements. Serum antigen titers for Histoplasma capsulatum demonstrated evidence of active infection. This case is a rare example of a supranuclear ocular motility disturbance and optic neuropathy secondary to an occlusive vascular process in a patient with subacute disseminated histoplasmosis.

Diagnostic Errors↗
PubMed1999

Are there site-specific differences among extranodal aggressive B-cell neoplasms?

Aggressive B-cell lymphomas, including diffuse large cell, Burkitt, and lymphoblastic types, may affect a wide variety of extranodal sites. Up to 40% of these tumors are initially diagnosed in extranodal locations. Regardless of site, these tumors have many histologic similarities; however, some clinical, cytologic, immunologic, and etiologic features of these tumors seem to be distinctive for particular sites of extranodal presentation. In accordance primarily with the extranodal locations presented at the Society for Hematopathology Fourth Slide Workshop on Extranodal Hematopoietic/Lymphoid Disorders (Excluding Bone Marrow and Spleen), the distinctive features of the aggressive B-cell lymphomas of the mediastinum, breast, bone, skin, and body cavities as well as the rare, but primarily extranodal intravascular lymphomatosis, will be discussed.

Humans↗
PubMed1998

Epstein-Barr virus detection in nasopharyngeal tissues of patients with suspected nasopharyngeal carcinoma.

BACKGROUND: Nasopharyngeal carcinoma (NPC) is strongly associated with Epstein-Barr virus (EBV). Detection of EBV in biopsy specimens may serve as a tumor marker. METHODS: To assess the sensitivity and specificity of the polymerase chain reaction (PCR) and in situ hybridization in the diagnosis of NPC, formalin fixed, paraffin embedded nasopharyngeal biopsies from patients in Taiwan suspected of having NPC were studied. RESULTS: In specimens from 107 patients with NPC, EBV was detected by PCR in 97 cases (90.7%) and by EBER in situ hybridization in 105 cases (98.1%). In specimens from 61 patients without neoplasia, EBV was detected by PCR in 7 cases (11.5%) and by EBER in situ hybridization in 0 cases. CONCLUSIONS: These results suggest that although EBV DNA may occasionally be detected in nonneoplastic nasopharyngeal tissues, cells expressing EBER are not. EBER in situ hybridization may therefore prove to be a useful adjunct in the diagnosis of NPC.

Biopsy↗
PubMed1997

Blastic natural killer cell leukemia/lymphoma: a clinicopathologic study.

The classification of natural killer (NK)-cell and NK-like T-cell malignancies has undergone significant evolution in recent years. Although examples of NK-cell tumors resembling acute leukemia have been described anecdotally as blastic, blastoid, or monomorphic NK-cell leukemia/lymphoma (NKL/L), the clinical and pathologic features of these tumors have not been systematically defined. We report four patients with blastic NKL/L and describe the clinical, pathologic, and immunophenotypic findings in these cases. All patients were elderly (58-82 years) and presented with cutaneous plaques. Two patients also had adenopathy, and three patients had marrow involvement at presentation. Biopsy of cutaneous lesions showed atypical superficial and deep dermal lymphoid infiltrates. Involved lymph nodes were architecturally effaced by an interfollicular infiltrate with blastic cytologic features. In Wright-Giemsa-stained blood or marrow smears, tumor cells had finely distributed nuclear chromatin, many with nucleoli, and variable amounts of cytoplasm. In contrast to many NK and NK-like T-cell disorders, azurophilic cytoplasmic granules were absent or inconspicuous. The tumor cells were immunophenotypically distinctive. They expressed intermediate density CD45, as is characteristic of blasts; in addition, the cells were positive for HLA-DR, CD2, CD4, and the NK-associated antigen CD56. Surface CD3, cytoplasmic CD3, and CD5 were negative in all cases tested, whereas CD7 was expressed in two cases. In formalin-fixed tissue, tumor cells marked with antibodies to CD43, but not with other T- or B-lineage-related antibodies. All three cases studied for Epstein-Barr viral RNA by in situ hybridization were negative. Although treatments varied, all three patients with clinical follow-up died within months of the diagnosis. The clinical course in two patients culminated in an overtly leukemic phase. These findings suggest that blastic NKL/L represents a distinct clinicopathologic entity, characterized by cutaneous, nodal, and marrow involvement by blastic cells with immunophenotypic characteristics of true NK cells. The disease afflicts elderly patients, pursues an aggressive course, and may culminate in overt leukemia.

Aged↗
PubMed1997

Molecular detection of bone marrow involvement in intravascular lymphomatosis.

Intravascular lymphomatosis (IVL) is an extremely rare variant of aggressive non-Hodgkin's lymphoma characterized by confinement of neoplastic lymphocytes within vascular spaces. Although IVL is potentially curable with combination chemotherapy, diagnosis is often delayed, in part owing to the negative bone marrow biopsy specimens that are typical of this disorder. We hypothesized that use of a more sensitive method of analysis might identify small clonal B-cell populations in histologically negative bone marrow biopsy specimens from patients with IVL. With use of a recently described assay for immunoglobulin heavy chain gene rearrangement based on the polymerase chain reaction, we demonstrated clonal B-cell populations in histologically negative marrow specimens from five (100%) of five patients with IVL. None of these specimens demonstrated molecular evidence of the t(14;18) associated with follicular lymphoma, providing no evidence for a common derivation of IVL and follicular lymphoma. In summary, molecular analysis of routine bone marrow biopsy sepcimens from patients in whom the diagnosis of IVL is entertained may facilitate prompt recognition of a lympho-proliferative disorder and thereby permit timely therapeutic intervention. Moreover, these findings suggest that despite histologically negative staging bone marrow biopsy specimens, IVL typically disseminates early in its course, thus arguing against the use of localized therapy in this disorder.

Aged↗