96 research outputs found
Greenhouse gas balance over thaw-freeze cycles in discontinuous zone permafrost
Peat in the discontinuous permafrost zone contains a globally significant reservoir of carbon that has undergone multiple permafrost-thaw cycles since the end of the mid-Holocene (~3700âyears before present). Periods of thaw increase C decomposition rates which leads to the release of CO2 and CH4 to the atmosphere creating potential climate feedback. To determine the magnitude and direction of such feedback, we measured CO2 and CH4 emissions and modeled C accumulation rates and radiative fluxes from measurements of two radioactive tracers with differing lifetimes to describe the C balance of the peatland over multiple permafrost-thaw cycles since the initiation of permafrost at the site. At thaw features, the balance between increased primary production and higher CH4 emission stimulated by warmer temperatures and wetter conditions favors C sequestration and enhanced peat accumulation. Flux measurements suggest that frozen plateaus may intermittently (order of years to decades) act as CO2 sources depending on temperature and net ecosystem respiration rates, but modeling results suggest thatâdespite brief periods of net C loss to the atmosphere at the initiation of thawâintegrated over millennia, these sites have acted as net C sinks via peat accumulation. In greenhouse gas terms, the transition from frozen permafrost to thawed wetland is accompanied by increasing CO2 uptake that is partially offset by increasing CH4 emissions. In the short-term (decadal time scale) the net effect of this transition is likely enhanced warming via increased radiative C emissions, while in the long-term (centuries) net C deposition provides a negative feedback to climate warming
Energy of Isolated Systems at Retarded Times as the Null Limit of Quasilocal Energy
We define the energy of a perfectly isolated system at a given retarded time
as the suitable null limit of the quasilocal energy . The result coincides
with the Bondi-Sachs mass. Our is the lapse-unity shift-zero boundary value
of the gravitational Hamiltonian appropriate for the partial system
contained within a finite topologically spherical boundary . Moreover, we show that with an arbitrary lapse and zero shift the same
null limit of the Hamiltonian defines a physically meaningful element in the
space dual to supertranslations. This result is specialized to yield an
expression for the full Bondi-Sachs four-momentum in terms of Hamiltonian
values.Comment: REVTEX, 16 pages, 1 figur
Hamiltonian thermodynamics of a Lovelock black hole
We consider the Hamiltonian dynamics and thermodynamics of spherically
symmetric spacetimes within a one-parameter family of five-dimensional Lovelock
theories. We adopt boundary conditions that make every classical solution part
of a black hole exterior, with the spacelike hypersurfaces extending from the
horizon bifurcation three-sphere to a timelike boundary with fixed intrinsic
metric. The constraints are simplified by a Kucha\v{r}-type canonical
transformation, and the theory is reduced to its true dynamical degrees of
freedom. After quantization, the trace of the analytically continued Lorentzian
time evolution operator is interpreted as the partition function of a
thermodynamical canonical ensemble. Whenever the partition function is
dominated by a Euclidean black hole solution, the entropy is given by the
Lovelock analogue of the Bekenstein-Hawking entropy; in particular, in the low
temperature limit the system exhibits a dominant classical solution that has no
counterpart in Einstein's theory. The asymptotically flat space limit of the
partition function does not exist. The results indicate qualitative robustness
of the thermodynamics of five-dimensional Einstein theory upon the addition of
a nontrivial Lovelock term.Comment: 22 pages, REVTeX v3.
A phase II study of dacetuzumab (SGN-40) in patients with relapsed diffuse large B-cell lymphoma (DLBCL) and correlative analyses of patient-specific factors
BACKGROUND: Patients with DLBCL who are ineligible for or have relapsed after aggressive salvage chemotherapy have a poor prognosis. CD40 is expressed on multiple B-cell neoplasms including DLBCL and is a potential target for immunotherapy. Dacetuzumab (SGN-40), a non-blocking, partial agonist, humanized IgG1, anti-CD40 monoclonal antibody, has previously demonstrated anti-lymphoma activity in a phase I study. METHODS: A phase II study was undertaken to evaluate the rate and duration of objective responses and safety of single-agent dacetuzumab in relapsed DLBCL. Forty-six adult patients with relapsed/refractory DLBCL received up to 12Â cycles of intravenous dacetuzumab using intrapatient dose-escalation to a target dose of 8Â mg/kg/week in an initial 5-week cycle, followed by 4-week cycles of 8Â mg/kg/week. Study endpoints included rate and duration of objective responses, safety, survival, pharmacokinetics, immunogenicity, and exploratory correlative studies. RESULTS: Overall response rate was 9% and disease control rate (complete remissionâ+âpartial remissionâ+âstable disease) was 37%. Common non-hematologic adverse events (AEs) included fatigue, headache, chills, fever, and nausea. The most frequent Grade 3â4 non-hematologic AE was deep venous thrombosis (3 patients). Grade 3â4 lymphopenia (41%), neutropenia (13%), or thrombocytopenia (19%) occurred without associated infection or bleeding. Reversible ocular events, including conjunctivitis and ocular hyperemia, occurred in 8 patients (17%). Patient-specific factors, including Fc-gamma-RIIIa polymorphism, did not appear to correlate with antitumor activity. CONCLUSIONS: Single-agent dacetuzumab has modest activity and manageable toxicity in unselected patients with relapsed DLBCL. Combination regimens and robust methods of patient selection may be necessary for further development. TRIAL REGISTRATION: ClinicalTrials.gov identifier NCT00435916
The FLASH pilot survey: an HI absorption search against MRC 1-Jy radio sources
We report an ASKAP search for associated HI 21-cm absorption against bright
radio sources from the Molonglo Reference Catalogue (MRC) 1-Jy sample. The
search uses pilot survey data from the ASKAP First Large Absorption Survey in
\hi (FLASH) covering the redshift range . From a sample of 62
MRC 1-Jy radio galaxies and quasars in this redshift range we report three new
detections of associated HI 21-cm absorption, yielding an overall detection
fraction of . The detected systems comprise two radio
galaxies (MRC 2216281 at and MRC 0531237 at ) and one
quasar (MRC 2156245 at ). The MRC 0531237 absorption system is
the strongest found to date, with a velocity integrated optical depth of . All three objects with detected HI 21-cm
absorption are peaked-spectrum or compact steep-spectrum (CSS) radio sources,
classified based on our SED fits to the spectra. Two of them show strong
interplanetary scintillation at 162 MHz, implying that the radio continuum
source is smaller than 1 arcsec in size even at low frequencies. Among the
class of peaked-spectrum and compact steep-spectrum radio sources, the HI
detection fraction is . This is consistent within
with a detection fraction of in
earlier reported GPS and CSS samples at intermediate redshifts (). All three detections have a high 1.4 GHz radio luminosity, with MRC
0531237 and MRC 2216281 having the highest values in the sample, . The preponderance of extended radio sources in our sample
could partially explain the overall low detection fraction, while the effects
of a redshift evolution in gas properties and AGN UV luminosity on the neutral
gas absorption still need to be investigated.Comment: 28 pages, 9 figures and 7 Tables. Submitted to MNRA
Quantum state preparation and macroscopic entanglement in gravitational-wave detectors
Long-baseline laser-interferometer gravitational-wave detectors are operating
at a factor of 10 (in amplitude) above the standard quantum limit (SQL) within
a broad frequency band. Such a low classical noise budget has already allowed
the creation of a controlled 2.7 kg macroscopic oscillator with an effective
eigenfrequency of 150 Hz and an occupation number of 200. This result, along
with the prospect for further improvements, heralds the new possibility of
experimentally probing macroscopic quantum mechanics (MQM) - quantum mechanical
behavior of objects in the realm of everyday experience - using
gravitational-wave detectors. In this paper, we provide the mathematical
foundation for the first step of a MQM experiment: the preparation of a
macroscopic test mass into a nearly minimum-Heisenberg-limited Gaussian quantum
state, which is possible if the interferometer's classical noise beats the SQL
in a broad frequency band. Our formalism, based on Wiener filtering, allows a
straightforward conversion from the classical noise budget of a laser
interferometer, in terms of noise spectra, into the strategy for quantum state
preparation, and the quality of the prepared state. Using this formalism, we
consider how Gaussian entanglement can be built among two macroscopic test
masses, and the performance of the planned Advanced LIGO interferometers in
quantum-state preparation
Searching for a Stochastic Background of Gravitational Waves with LIGO
The Laser Interferometer Gravitational-wave Observatory (LIGO) has performed
the fourth science run, S4, with significantly improved interferometer
sensitivities with respect to previous runs. Using data acquired during this
science run, we place a limit on the amplitude of a stochastic background of
gravitational waves. For a frequency independent spectrum, the new limit is
. This is currently the most sensitive
result in the frequency range 51-150 Hz, with a factor of 13 improvement over
the previous LIGO result. We discuss complementarity of the new result with
other constraints on a stochastic background of gravitational waves, and we
investigate implications of the new result for different models of this
background.Comment: 37 pages, 16 figure
Search for gravitational wave bursts in LIGO's third science run
We report on a search for gravitational wave bursts in data from the three
LIGO interferometric detectors during their third science run. The search
targets subsecond bursts in the frequency range 100-1100 Hz for which no
waveform model is assumed, and has a sensitivity in terms of the
root-sum-square (rss) strain amplitude of hrss ~ 10^{-20} / sqrt(Hz). No
gravitational wave signals were detected in the 8 days of analyzed data.Comment: 12 pages, 6 figures. Amaldi-6 conference proceedings to be published
in Classical and Quantum Gravit
Qualitative analysis of how patients decide that they want risk-reducing mastectomy, and the implications for surgeons in responding to emotionally-motivated patient requests
Objective
Contemporary approaches to medical decision-making advise that clinicians should respect patientsâ decisions. However, patientsâ decisions are often shaped by heuristics, such as being guided by emotion, rather than by objective risk and benefit. Risk-reducing mastectomy (RRM) decisions focus this dilemma sharply. RRM reduces breast cancer (BC) risk, but is invasive and can have iatrogenic consequences. Previous evidence suggests that emotion guides patientsâ decision-making about RRM. We interviewed patients to better understand how they made decisions about RRM, using findings to consider how clinicians could ethically respond to their decisions.
Methods
Qualitative face-to-face interviews with 34 patients listed for RRM surgery and two who had decided against RRM.
Results
Patients generally did not use objective risk estimates or, indeed, consider risks and benefits of RRM. Instead emotions guided their decisions: they chose RRM because they feared BC and wanted to do âall they couldâ to prevent it. Most therefore perceived RRM to be the âobviousâ option and made the decision easily. However, many recounted extensive post-decisional deliberation, generally directed towards justifying the original decision. A few patients deliberated before the decision because fears of surgery counterbalanced those of BC.
Conclusion
Patients seeking RRM were motivated by fear of BC, and the need to avoid potential regret for not doing all they could to prevent it. We suggest that choices such as that for RRM, which are made emotionally, can be respected as autonomous decisions, provided patients have considered risks and benefits. Drawing on psychological theory about how people do make decisions, as well as normative views of how they should, we propose that practitioners can guide consideration of risks and benefits even, where necessary, after patients have opted for surgery. This model of practice could be extended to other medical decisions that are influenced by patientsâ emotions
- âŠ