12,931 research outputs found

### `Sinking' in a bed of grains activated by shearing

We show how a weak force, $f$, enables intruder motion through dense granular
materials subject to external mechanical excitations, in the present case
stepwise shearing. A force acts on a Teflon disc in a two dimensional system of
photoelastic discs. This force is much smaller than the smallest force needed
to move the disc without any external excitation. In a cycle, material +
intruder are sheared quasi-statically from $\gamma = 0$ to $\gamma_{max}$, and
then backwards to $\gamma = 0$. During various cycle phases, fragile and jammed
states form. Net intruder motion, $\delta$, occurs during fragile periods
generated by shear reversals. $\delta$ per cycle, e.g. the quasistatic rate
$c$, is constant, linearly dependent on $\gamma_{max}$ and $f$. It vanishes as,
$c \propto (\phi_c - \phi)^a$, with $a \simeq 3$ and $\phi_c \simeq \phi_J$,
reflecting the stiffening of granular systems under shear as $\phi \rightarrow
\phi_J$. The intruder motion induces large scale grain circulation. In the
intruder frame, this motion is a granular analogue to fluid flow past a
cylinder, where $f$ is the drag force exerted by the flow.Comment: 4 pages, 5 figures letter with supplementarie

### Revisiting the $B$-physics anomalies in $R$-parity violating MSSM

In recent years, several deviations from the Standard Model predictions in
semileptonic decays of $B$-meson might suggest the existence of new physics
which would break the lepton-flavour universality. In this work, we have
explored the possibility of using muon sneutrinos and right-handed sbottoms to
solve these $B$-physics anomalies simultaneously in $R$-parity violating
minimal supersymmetric standard model. We find that the photonic penguin
induced by exchanging sneutrino can provide sizable lepton flavour universal
contribution due to the existence of logarithmic enhancement for the first
time. This prompts us to use the two-parameter scenario $(C^{\rm V}_9, \,
C^{\rm U}_9)$ to explain $b \to s \ell^+ \ell^-$ anomaly. Finally, the
numerical analyses show that the muon sneutrinos and right-handed sbottoms can
explain $b \to s \ell^+ \ell^-$ and $R(D^{(\ast)})$ anomalies simultaneously,
and satisfy the constraints of other related processes, such as $B \to
K^{(\ast)} \nu \bar\nu$ decays, $B_s-\bar B_s$ mixing, $Z$ decays, as well as
$D^0 \to \mu^+ \mu^-$, $\tau \to \mu \rho^0$, $B \to \tau \nu$, $D_s \to \tau
\nu$, $\tau \to K \nu$, $\tau \to \mu \gamma$, and $\tau \to \mu\mu\mu$ decays.Comment: 10 pages, 8 figures, matches to the version published in EPJ

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### A regioselectivity switch in Pd-catalyzed hydroallylation of alkynes.

By exploiting the reactivity of a vinyl-Pd species, we control the regioselectivity in hydroallylation of alkynes under Pd-hydride catalysis. A monophosphine ligand and carboxylic acid combination promotes 1,5-dienes through a pathway involving isomerization of alkynes to allenes. In contrast, a bisphosphine ligand and copper cocatalyst favor 1,4-dienes via a mechanism that involves transmetalation. Our study highlights how to access different isomers by diverting a common organometallic intermediate

### Optical spectroscopy study on CeTe$_3$: evidence for multiple charge-density-wave orders

We performed optical spectroscopy measurement on single crystal of CeTe$_3$,
a rare-earth element tri-telluride charge density wave (CDW) compound. The
optical spectra are found to display very strong temperature dependence.
Besides a large and pronounced CDW energy gap being present already at room
temperature as observed in earlier studies, the present measurement revealed
the formation of another energy gap at smaller energy scale at low temperature.
The second CDW gap removes the electrons near E$_F$ which undergo stronger
scattering. The study yields evidence for the presence of multiple CDW orders
or strong fluctuations in the light rare-earth element tri-telluride.Comment: 5 figure

### Physics-informed Neural Network Combined with Characteristic-Based Split for Solving Navier-Stokes Equations

In this paper, physics-informed neural network (PINN) based on
characteristic-based split (CBS) is proposed, which can be used to solve the
time-dependent Navier-Stokes equations (N-S equations). In this method, The
output parameters and corresponding losses are separated, so the weights
between output parameters are not considered. Not all partial derivatives
participate in gradient backpropagation, and the remaining terms will be
reused.Therefore, compared with traditional PINN, this method is a rapid
version. Here, labeled data, physical constraints and network outputs are
regarded as priori information, and the residuals of the N-S equations are
regarded as posteriori information. So this method can deal with both
data-driven and data-free problems. As a result, it can solve the special form
of compressible N-S equations -- -Shallow-Water equations, and incompressible
N-S equations. As boundary conditions are known, this method only needs the
flow field information at a certain time to restore the past and future flow
field information. We solve the progress of a solitary wave onto a shelving
beach and the dispersion of the hot water in the flow, which show this method's
potential in the marine engineering. We also use incompressible equations with
exact solutions to prove this method's correctness and universality. We find
that PINN needs more strict boundary conditions to solve the N-S equation,
because it has no computational boundary compared with the finite element
method

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