1,267 research outputs found
NEXUS/Physics: An interdisciplinary repurposing of physics for biologists
In response to increasing calls for the reform of the undergraduate science
curriculum for life science majors and pre-medical students (Bio2010,
Scientific Foundations for Future Physicians, Vision & Change), an
interdisciplinary team has created NEXUS/Physics: a repurposing of an
introductory physics curriculum for the life sciences. The curriculum interacts
strongly and supportively with introductory biology and chemistry courses taken
by life sciences students, with the goal of helping students build general,
multi-discipline scientific competencies. In order to do this, our two-semester
NEXUS/Physics course sequence is positioned as a second year course so students
will have had some exposure to basic concepts in biology and chemistry.
NEXUS/Physics stresses interdisciplinary examples and the content differs
markedly from traditional introductory physics to facilitate this. It extends
the discussion of energy to include interatomic potentials and chemical
reactions, the discussion of thermodynamics to include enthalpy and Gibbs free
energy, and includes a serious discussion of random vs. coherent motion
including diffusion. The development of instructional materials is coordinated
with careful education research. Both the new content and the results of the
research are described in a series of papers for which this paper serves as an
overview and context.Comment: 12 page
Tunneling Conductance and Coulomb Blockade Peak Splitting of Two Quantum Dots Connected by a Quantum Point Contact
By using bosonization method and unitary transformation, we give a general
relation between the dimensionless tunneling conductance and the fractional
Coulomb blockade conductance peak splitting which is valid both for weak and
strong transmission between two quantum dots, and show that the tunneling
conductance has a linear temperature dependence in the low energy and low
temperature limit.Comment: 12 pages, Revtex, no figures, to appear in Phys. Rev.
Mesoscopic Coulomb Blockade in One-channel Quantum Dots
Signatures of "mesoscopic Coulomb blockade" are reported for quantum dots
with one fully transmitting point-contact lead, T1 = 1, T2 << 1. Unlike Coulomb
blockade (CB) in weak-tunneling devices (T1, T2 << 1), one-channel CB is a
mesoscopic effect requiring quantum coherence. Several distinctive features of
mesoscopic CB are observed, including a reduction in CB upon breaking
time-reversal symmetry with a magnetic field, relatively large fluctuations of
peak position as a function of magnetic field, and strong temperature
dependence on the scale of the quantum level spacing.Comment: 12 pages, including 4 figure
Cubic polynomials on Lie groups: reduction of the Hamiltonian system
This paper analyzes the optimal control problem of cubic polynomials on
compact Lie groups from a Hamiltonian point of view and its symmetries. The
dynamics of the problem is described by a presymplectic formalism associated
with the canonical symplectic form on the cotangent bundle of the semidirect
product of the Lie group and its Lie algebra. Using these control geometric
tools, the relation between the Hamiltonian approach developed here and the
known variational one is analyzed. After making explicit the left trivialized
system, we use the technique of Marsden-Weinstein reduction to remove the
symmetries of the Hamiltonian system. In view of the reduced dynamics, we are
able to guarantee, by means of the Lie-Cartan theorem, the existence of a
considerable number of independent integrals of motion in involution.Comment: 20 pages. Final version which incorporates the Corrigendum recently
published (J. Phys. A: Math. Theor. 46 189501, 2013
Higher-Order Results for the Relation between Channel Conductance and the Coulomb Blockade for Two Tunnel-Coupled Quantum Dots
We extend earlier results on the relation between the dimensionless tunneling
channel conductance and the fractional Coulomb blockade peak splitting
for two electrostatically equivalent dots connected by an arbitrary number
of tunneling channels with bandwidths much larger than the
two-dot differential charging energy . By calculating through second
order in in the limit of weak coupling (), we illuminate
the difference in behavior of the large- and
small- regimes and make more plausible extrapolation to the
strong-coupling () limit. For the special case of
and strong coupling, we eliminate an apparent ultraviolet
divergence and obtain the next leading term of an expansion in . We show
that the results we calculate are independent of such band structure details as
the fraction of occupied fermionic single-particle states in the weak-coupling
theory and the nature of the cut-off in the bosonized strong-coupling theory.
The results agree with calculations for metallic junctions in the
limit and improve the previous good
agreement with recent two-channel experiments.Comment: 27 pages, 1 RevTeX file with 4 embedded Postscript figures. Uses eps
Tunneling through a multigrain system: deducing the sample topology from the nonlinear conductance
We study a current transport through a system of a few grains connected with
tunneling links. The exact solution is given for an arbitrarily connected
double-grain system with a shared gate in the framework of the orthodox model.
The obtained result is generalized for multigrain systems with strongly
different tunneling resistances. We analyse the large-scale nonlinear
conductance and demonstrate how the sample topology can be unambiguously
deduced from the spectroscopy pattern (differential conductance versus
gate-bias plot). We present experimental data for a multigrain sample and
reconstruct the sample topology. A simple selection rule is formulated to
distinguish samples with spectral patterns free from spurious disturbance
caused by recharging of some grains nearby. As an example, we demonstrate
experimental data with additional peaks in the spectroscopy pattern, which can
not be attributed to coupling to additional grains. The described approach can
be used to judge the sample topology when it is not guaranteed by fabrication
and direct imaging is not possible.Comment: 13 pages (including 8 figures
Atmospheric Muon Flux at Sea Level, Underground, and Underwater
The vertical sea-level muon spectrum at energies above 1 GeV and the
underground/underwater muon intensities at depths up to 18 km w.e. are
calculated. The results are particularly collated with a great body of the
ground-level, underground, and underwater muon data. In the hadron-cascade
calculations, the growth with energy of inelastic cross sections and pion,
kaon, and nucleon generation in pion-nucleus collisions are taken into account.
For evaluating the prompt muon contribution to the muon flux, we apply two
phenomenological approaches to the charm production problem: the recombination
quark-parton model and the quark-gluon string model. To solve the muon
transport equation at large depths of homogeneous medium, a semi-analytical
method is used. The simple fitting formulas describing our numerical results
are given. Our analysis shows that, at depths up to 6-7 km w. e., essentially
all underground data on the muon intensity correlate with each other and with
predicted depth-intensity relation for conventional muons to within 10%.
However, the high-energy sea-level data as well as the data at large depths are
contradictory and cannot be quantitatively decribed by a single nuclear-cascade
model.Comment: 47 pages, REVTeX, 15 EPS figures included; recent experimental data
and references added, typos correcte
Using collective intelligence to identify barriers to teaching 12–19 year olds about the ocean in Europe
Since the degradation of the marine environment is strongly linked to human activities, having citizens who appreciate the ocean's influence on them and their influence on the ocean is important. Research has shown that citizens have a limited understanding of the ocean and it is this lack of ocean literacy that needs to change. This study maps the European landscape of barriers to teaching 12–19 year olds about the ocean, through the application of Collective Intelligence, a facilitation and problem solving methodology. The paper presents a meta-analysis of the 657 barriers to teaching about the ocean, highlighting how these barriers are interconnected and influence one another in a European Influence Map. The influence map shows 8 themes: Awareness and Perceived knowledge; Policies and Strategies; Engagement, formal education sector; the Ocean itself; Collaboration; Connections between humans and the ocean and the Blue Economy, having the greatest influence and impact on marine education. “Awareness and Perceived knowledge” in Stage 1, exerts the highest level of overall influence in teaching 12–19 year olds about the ocean. This map and study serves as a roadmap for policy makers to implement mobilisation actions that could mitigate the barriers to teaching about the ocean. Examples of such actions include free marine education learning resources such as e-books, virtual laboratories or hands-on experiments. Thus, supporting educators in taking on the challenge of helping our youth realise that the ocean supports life on Earth is essential for education, the marine and human well-being
Corrections to the universal behavior of the Coulomb-blockade peak splitting for quantum dots separated by a finite barrier
Building upon earlier work on the relation between the dimensionless interdot
channel conductance g and the fractional Coulomb-blockade peak splitting f for
two electrostatically equivalent dots, we calculate the leading correction that
results from an interdot tunneling barrier that is not a delta-function but,
rather, has a finite height V and a nonzero width xi and can be approximated as
parabolic near its peak. We develop a new treatment of the problem for g much
less than 1 that starts from the single-particle eigenstates for the full
coupled-dot system. The finiteness of the barrier leads to a small upward shift
of the f-versus-g curve at small values of g. The shift is a consequence of the
fact that the tunneling matrix elements vary exponentially with the energies of
the states connected. Therefore, when g is small, it can pay to tunnel to
intermediate states with single-particle energies above the barrier height V.
The correction to the zero-width behavior does not affect agreement with recent
experimental results but may be important in future experiments.Comment: Title changed from ``Non-universal...'' to ``Corrections to the
universal...'' No other changes. 10 pages, 1 RevTeX file with 2 postscript
figures included using eps
Dynamics of a mesoscopic qubit under continuous quantum measurement
We present the conditional quantum dynamics of an electron tunneling between
two quantum dots subject to a measurement using a low transparency point
contact or tunnel junction. The double dot system forms a single qubit and the
measurement corresponds to a continuous in time readout of the occupancy of the
quantum dot. We illustrate the difference between conditional and unconditional
dynamics of the qubit. The conditional dynamics is discussed in two regimes
depending on the rate of tunneling through the point contact: quantum jumps, in
which individual electron tunneling current events can be distinguished, and a
diffusive dynamics in which individual events are ignored, and the
time-averaged current is considered as a continuous diffusive variable. We
include the effect of inefficient measurement and the influence of the relative
phase between the two tunneling amplitudes of the double dot/point contact
system.Comment: 12 pages (one-column Revtex), 7 figure
- …