19 research outputs found
Thermocline Dynamics and Nitrogen Cycling Drive Productivity Shifts in the South China Sea Across Glacial Cycles
No full textThe South China Sea (SCS) nitrogen cycle responds dynamically to glacial–interglacial climate changes, yet the drivers of nitrogen isotope variability remain debated. We present a synthesis of foraminifera‐bound δ15N (FB‐δ15N) records, together with complementary organic and amino‐acid δ15N data from across the SCS. In the eastern and northern SCS, FB‐δ15N peaks during glacials when intensified East Asian Winter Monsoons shoal the thermocline, enhance upwelling of 15N‐enriched deep nitrate, and stimulate export production. Conversely, western and southern SCS records exhibit δ15N minima during interglacials, reflecting enhanced nitrogen fixation and/or partial nitrate utilization. This east–west divergence highlights the important role of upper‐ocean structure in modulating nitrogen isotopes, alongside potential sea‐level–driven nutrient effects. Our results establish FB‐δ15N as a sensitive proxy for reconstructing nutrient dynamics and monsoon‐driven upwelling in marginal seas and underscore the influence of thermocline variability in shaping marine nitrogen cycling over glacial cycles
A covariant entropy conjecture on cosmological dynamical horizon
No full textWe here propose a covariant entropy conjecture on cosmological dynamical horizon. After the formulation of our conjecture, we test its validity in adiabatically expanding universes with open, flat and closed spatial geometry, where our conjecture can also be viewed as a cosmological version of the generalized second law of thermodynamics in some sense.Physics, Particles & FieldsSCI(E)0ARTICLE10nul
The covariant entropy conjecture and concordance cosmological models
No full textRecently a covariant entropy conjecture has been proposed for dynamical horizons. We apply this conjecture to concordance cosmological models, namely, those cosmological models filled with perfect fluids, in the presence of a positive cosmological constant. As a result, we find that this conjecture has a severe constraint power. Not only does this conjecture rule out those cosmological models disfavored by the anthropic principle, but also it imposes an upper bound 10(-60) on the cosmological constant for our own universe, which thus provides an alternative macroscopic perspective for understanding the long-standing cosmological constant problem.Astronomy & AstrophysicsPhysics, Particles & FieldsSCI(E)0ARTICLE10nul
A COVARIANT ENTROPY BOUND CONJECTURE ON THE DYNAMICAL HORIZON
No full textWe propose, as a compelling pattern for the holographic principle, a covariant entropy bound conjecture for more general dynamical horizons. Then we apply our conjecture to Lambda CDM cosmological models, where we find that it imposes a novel upper bound, 10(-90), on the cosmological constant for our own universe by taking into account the dominant entropy contribution from supermassive black holes, which thus provides an alternative macroscopic perspective for understanding the long-standing cosmological constant problem. As an intriguing implication of this conjecture, we also discuss the possible profound relation between the present cosmological constant, the origin of mass, and the anthropic principle.Astronomy & AstrophysicsSCI(E)0ARTICLE13-142467-24741
The black hole dynamical horizon and generalized second law of thermodynamics
No full textThe generalized second law of thermodynamics for a system containing a black hole dynamical horizon is proposed in a covariant way. Its validity is also tested in case of adiabatically collapsing thick light shells.Physics, Particles & FieldsSCI(E)0ARTICLE12nul
Entanglement entropy: Helicity versus spin
No full textFor a massive spin 1/2 field, we present the reduced spin and helicity density matrix, respectively, for the same pure one particle state. Their relation has also been developed. Furthermore, we calculate and compare the corresponding entanglement entropy for spin and helicity within the same inertial reference frame. Due to the distinct dependence on momentum degree of freedom between spin and helicity states, the resultant helicity entropy is different from that of spin in general. In particular, we find that both helicity entanglement for a spin eigenstate and spin entanglement for a right handed or left handed helicity state do not vanish, and their Von Neumann entropy has no dependence on the specific form of momentum distribution, as long as it is isotropic.Computer Science, Theory & MethodsPhysics, Particles & FieldsPhysics, MathematicalSCI(E)5ARTICLE1181-186
HELICITY ENTANGLEMENT OF MOVING BODIES
No full textWe investigate the Lorentz transformation of the reduced helicity density matrix for a pair of massive spin 1/2 particles. The corresponding Wootters concurrence shows no invariant meaning, which implies that we can generate helicity entanglement simply by the transformation from one reference frame to another. The difference between the helicity and spin case is also discussed.Computer Science, Theory & MethodsPhysics, Particles & FieldsPhysics, MathematicalSCI(E)0ARTICLE2539-545
Quantum helicity entropy of moving bodies
No full textLorentz transformation of the reduced helicity density matrix for a massive spin-1/2 particle is investigated in the framework of relativistic quantum information theory for the first time. The corresponding helicity entropy is calculated, which shows no invariant meaning as that of spin. The variation of the helicity entropy with the relative speed of motion of inertial observers, however, differs significantly from that of spin due to their distinct transformation behaviors under the action of the Lorentz group. This novel and odd behavior unique to the helicity may be readily detected by high-energy physics experiments. The underlying physical explanations are also discussed.Physics, MultidisciplinaryPhysics, MathematicalSCI(E)0ARTICLE36F857-F8624
The kinematics of particles moving in rainbow spacetime
No full textThe kinematics of massive particles moving in rainbow spacetime is studied. We derive the equation of geodesics when the semiclassical effect of moving particles on the background is taken into account. In particular we show that in rainbow flat spacetime the trajectory of a freely falling particle remains unchanged which is still a straight line in energy-independent coordinate system. The implication to the Unruh effect in rainbow flat spacetime is also discussed.Physics, NuclearPhysics, Particles & FieldsPhysics, MathematicalSCI(E)0ARTICLE382931-29382
