59 research outputs found
Bimodal Distribution of Sulfuric Acid Aerosols in the Upper Haze of Venus
The upper haze (UH) of Venus is variable on the order of days and it is
populated by two particle modes. We use a 1D microphysics and vertical
transport model based on the Community Aerosol and Radiation Model for
Atmospheres to evaluate whether interaction of upwelled cloud particles and
sulfuric acid particles nucleated in situ on meteoric dust are able to generate
the two size modes and whether their observed variability are due to cloud top
vertical transient winds. Nucleation of photochemically produced sulfuric acid
onto polysulfur condensation nuclei generates mode 1 cloud droplets that then
diffuse upwards into the UH. Droplets generated in the UH from nucleation of
sulfuric acid onto meteoric dust coagulate with the upwelled cloud particles
and cannot reproduce the observed bimodal size distribution. The mass transport
enabled by cloud top transient winds are able to generate a bimodal size
distribution in a time scale consistent with observations. Sedimentation and
convection in the middle and lower clouds causes the formation of large mode 2
and mode 3 particles. Evaporation of these particles below the clouds creates a
local sulfuric acid vapor maximum that causes upwelling of sulfuric acid back
into the clouds. If the polysulfur condensation nuclei are small and their
production rate is high, coagulation of small droplets onto larger droplets in
the middle cloud may result in sulfuric acid "rain" below the clouds once every
few Earth months. Reduction of the polysulfur condensation nuclei production
rate destroys this oscillation and reduces the mode 1 particle abundance in the
middle cloud by two orders of magnitude, though it better reproduces the
sulfur-to-sulfuric-acid mass ratio in the cloud and haze droplets. In general
we find satisfactory agreement between our results and observations, though
improvements could be made by incorporating sulfur microphysics.Comment: 62 pages, 18 figures, 1 table. Accepted for publication in Icaru
Observation of critical phenomena and self-similarity in the gravitational collapse of radiation fluid
We observe critical phenomena in spherical collapse of radiation fluid. A
sequence of spacetimes is numerically computed, containing
models () that adiabatically disperse and models () that
form a black hole. Near the critical point (), evolutions develop a
self-similar region within which collapse is balanced by a strong,
inward-moving rarefaction wave that holds constant as a function of a
self-similar coordinate . The self-similar solution is known and we show
near-critical evolutions asymptotically approaching it. A critical exponent
is found for supercritical () models.Comment: 10 pages (LaTeX) (to appear in Phys. Rev. Lett.), TAR-039-UN
CP Violation in B -> pi+ pi- and the Unitarity Triangle
We analyze the extraction of weak phases from CP violation in
decays. We propose to determine the unitarity triangle
by combining the information on mixing induced CP
violation in , , with the precision observable
obtained from the CP asymmetry in . It is then possible to write
down exact analytical expressions for and as simple
functions of the observables and , and of the penguin
parameters and . As an application clean lower bounds on
and can be derived as functions of and ,
essentially without hadronic uncertainty. Computing and within QCD
factorization yields precise determinations of and since
the dependence on and is rather weak. It is emphasized that the
sensitivity to the phase enters only at second order and is extremely
small for moderate values of this phase, predicted in the heavy-quark limit.
Transparent analytical formulas are further given and discussed for the
parameter of direct CP violation in . We also discuss
alternative ways to analyze and that can be useful if new physics
affects -- mixing. Predictions and uncertainties for and
in QCD factorization are examined in detail. It is pointed out that a
simultaneous expansion in and 1/N leads to interesting simplifications.
At first order infrared divergences are absent, while the most important
effects are retained. Independent experimental tests of the factorization
framework are briefly discussed.Comment: 26 pages, 7 figure
The Potential Impact of Nuclear Conflict on Ocean Acidification
We demonstrate that the global cooling resulting from a range of nuclear conflict scenarios would temporarily increase the pH in the surface ocean by up to 0.06 units over a 5-year period, briefly alleviating the decline in pH associated with ocean acidification. Conversely, the global cooling dissolves atmospheric carbon into the upper ocean, driving a 0.1 to 0.3 unit decrease in the aragonite saturation state (Ωarag) that persists for ∼10 years. The peak anomaly in pH occurs 2 years post conflict, while the Ωarag anomaly peaks 4- to 5-years post conflict. The decrease in Ωarag would exacerbate a primary threat of ocean acidification: the inability of marine calcifying organisms to maintain their shells/skeletons in a corrosive environment. Our results are based on sensitivity simulations conducted with a state-of-the-art Earth system model integrated under various black carbon (soot) external forcings. Our findings suggest that regional nuclear conflict may have ramifications for global ocean acidification
Rapidly expanding nuclear arsenals in Pakistan and India portend regional and global catastrophe
Pakistan and India may have 400 to 500 nuclear weapons by 2025 with yields from tested 12- to 45-kt values to a few hundred kilotons. If India uses 100 strategic weapons to attack urban centers and Pakistan uses 150, fatalities could reach 50 to 125 million people, and nuclear-ignited fires could release 16 to 36 Tg of black carbon in smoke, depending on yield. The smoke will rise into the upper troposphere, be self-lofted into the stratosphere, and spread globally within weeks. Surface sunlight will decline by 20 to 35%, cooling the global surface by 2° to 5°C and reducing precipitation by 15 to 30%, with larger regional impacts. Recovery takes more than 10 years. Net primary productivity declines 15 to 30% on land and 5 to 15% in oceans threatening mass starvation and additional worldwide collateral fatalities
Marine wild-capture fisheries after nuclear war
Unidad de excelencia María de Maeztu CEX2019-000940-MIdentificadors digitals: Digital object identifier for the 'European Research Council' (http://dx.doi.org/10.13039/501100000781) Digital object identifier for 'Horizon 2020' (http://dx.doi.org/10.13039/501100007601) - BIGSEA projectNuclear war, beyond its devastating direct impacts, is expected to cause global climatic perturbations through injections of soot into the upper atmosphere. Reduced temperature and sunlight could drive unprecedented reductions in agricultural production, endangering global food security. However, the effects of nuclear war on marine wild-capture fisheries, which significantly contribute to the global animal protein and micronutrient supply, remain unexplored. We simulate the climatic effects of six war scenarios on fish biomass and catch globally, using a state-of-the-art Earth system model and global process-based fisheries model. We also simulate how either rapidly increased fish demand (driven by food shortages) or decreased ability to fish (due to infrastructure disruptions), would affect global catches, and test the benefits of strong prewar fisheries management. We find a decade-long negative climatic impact that intensifies with soot emissions, with global biomass and catch falling by up to 18 ± 3% and 29 ± 7% after a US-Russia war under business-as-usual fishing-similar in magnitude to the end-of-century declines under unmitigated global warming. When war occurs in an overfished state, increasing demand increases short-term (1 to 2 y) catch by at most ∼30% followed by precipitous declines of up to ∼70%, thus offsetting only a minor fraction of agricultural losses. However, effective prewar management that rebuilds fish biomass could ensure a short-term catch buffer large enough to replace ∼43 ± 35% of today's global animal protein production. This buffering function in the event of a global food emergency adds to the many previously known economic and ecological benefits of effective and precautionary fisheries management
Marine wild-capture fisheries after nuclear war
Nuclear war, beyond its devastating direct impacts, is expected to cause global climatic perturbations through injections of soot into the upper atmosphere. Reduced temperature and sunlight could drive unprecedented reductions in agricultural production, endangering global food security. However, the effects of nuclear war on marine wild-capture fisheries, which significantly contribute to the global animal protein and micronutrient supply, remain unexplored. We simulate the climatic effects of six war scenarios on fish biomass and catch globally, using a state-of-the-art Earth system model and global process-based fisheries model. We also simulate how either rapidly increased fish demand (driven by food shortages) or decreased ability to fish (due to infrastructure disruptions), would affect global catches, and test the benefits of strong prewar fisheries management. We find a decade-long negative climatic impact that intensifies with soot emissions, with global biomass and catch falling by up to 18 ± 3% and 29 ± 7% after a US–Russia war under business-as-usual fishing—similar in magnitude to the end-of-century declines under unmitigated global warming. When war occurs in an overfished state, increasing demand increases short-term (1 to 2 y) catch by at most ∼30% followed by precipitous declines of up to ∼70%, thus offsetting only a minor fraction of agricultural losses. However, effective prewar management that rebuilds fish biomass could ensure a short-term catch buffer large enough to replace ∼43 ± 35% of today’s global animal protein production. This buffering function in the event of a global food emergency adds to the many previously known economic and ecological benefits of effective and precautionary fisheries management
The s ---> d gamma decay in and beyond the Standard Model
The New Physics sensitivity of the s ---> d gamma transition and its
accessibility through hadronic processes are thoroughly investigated. Firstly,
the Standard Model predictions for the direct CP-violating observables in
radiative K decays are systematically improved. Besides, the magnetic
contribution to epsilon prime is estimated and found subleading, even in the
presence of New Physics, and a new strategy to resolve its electroweak versus
QCD penguin fraction is identified. Secondly, the signatures of a series of New
Physics scenarios, characterized as model-independently as possible in terms of
their underlying dynamics, are investigated by combining the information from
all the FCNC transitions in the s ---> d sector.Comment: 54 pages, 14 eps figure
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