242 research outputs found
Measurement Based Quantum Heat Engine with Coupled Working Medium
We consider measurement based single temperature quantum heat engine without
feedback control, introduced recently by Yi, Talkner and Kim [Phys. Rev. E 96,
022108 (2017)]. Taking the working medium of the engine to be a one-dimensional
Heisenberg model of two spins, we calculate the efficiency of the engine
undergoing a cyclic process. Starting with two spin-1/2 particles, we
investigate the scenario of higher spins also. We show that, for this model of
coupled working medium, efficiency can be higher than that of an uncoupled one.
However, the relationship between the coupling constant and the efficiency of
the engine is rather involved. We find that in the higher spin scenario
efficiency can sometimes be negative (this means work has to be done to run the
engine cycle) for certain range of coupling constants, in contrast to the
aforesaid work of Yi, Talkner and Kim, where they showed that the extracted
work is always positive in the absence of coupling. We provide arguments for
this negative efficiency in higher spin scenarios. Interestingly, this happens
only in the asymmetric scenarios, where the two spins are different. Given
these facts, for judiciously chosen conditions, an engine with coupled working
medium gives advantage for the efficiency over the uncoupled one.Comment: 15 pages, 17 figures, published versio
Twitter Sentiment Analysis of Major US Topics
The user base for social media platforms have seen sharp increases in nearly every year since their inception, to the point where it is a part of a daily routine in today’s society. Social media provides a powerful public platform for people to express their opinions and intentions regarding almost any topic. The objective of this study was to determine how the opinions of topics related to United States politics shift over the course of the election cycle and through the inauguration of the next president. These topics included the opinions of major events such as the major presidential candidates Joe Biden and Donald Trump, appointment of Supreme Court Justice Amy Coney Barrett, the #BlackLivesMatter movement, the 2021 Storming of the United States Capitol, and the controversy surrounding mail-in ballots. The Twitter API was accessed using the tweepy library to survey public opinion and collect the sample size of over 1 million tweets. The data was then analyzed using the nltk and text2emotion libraries. The sentiment of the tweets were analyzed by search keyword, by date, and by sentiment over time by keyword
Contribution of deformation-induced martensite to fracture appearance of austenitic stainless steel
Fracture surface commonly carries the evidence of high-energy (ductile/tough) and low-energy (brittle) regions involved in fracture history, the macroscopic appearance of a fracture surface has often been utilised to qualitatively evaluate toughness of materials. For metastable austenitic stainless steels (AISI 304LN), the degree of martensitic transformation affects the fracture appearance and thus depends critically on the strain rate. The two dimensional ductile tearing ridge pattern quantified from many tensile fractographs are observed to predict the nature of disparity in deformation and fracture responses with systematic variation in strain rate of the steel under ambient atmosphere. The spatial distribution of deformation-induced martensite under tension at various stress/strains and strain rates strongly influences void nucleation, growth, coalescence and hence, keeps the impression on the ductile tearing ridge morphologies and dimple geometries on the fracture surface, where the initial inclusion content was constant
Distinguishing different classes of entanglement of three-qubit pure states
Employing the Pauli matrices, we have constructed a set of operators, which
can be used to distinguish six inequivalent classes of entanglement under SLOCC
(stochastic local operation and classical communication) for three-qubit pure
states. These operators have very simple structure and can be obtained from the
Mermin's operator with suitable choice of directions. Moreover these operators
may be implemented in an experiment to distinguish the types of entanglement
present in a state. We show that the measurement of only one operator is
sufficient to distinguish GHZ class from rest of the classes. It is also shown
that it is possible to detect and classify other classes by performing a small
number of measurements. We also show how to construct such observables in any
basis. We also consider a few mixed states to investigate the usefulness of our
operators. Furthermore, we consider the teleportation scheme of Lee et al.
(Phys. Rev. A 72, 024302 (2005)) and show that the partial tangles and hence
teleportation fidelity can be measured. We have also shown that these partial
tangles can also be used to classify genuinely entangled state, biseparable
state and separable state.Comment: 7 pages, 2 figures, comments welcom
Two-qubit mixed states and teleportation fidelity: Purity, concurrence, and beyond
To explore the properties of a two-qubit mixed state, we consider quantum
teleportation. The fidelity of a teleported state depends on the resource state
purity and entanglement, as characterized by concurrence. Concurrence and
purity are functions of state parameters. However, it turns out that a state
with larger purity and concurrence, may have comparatively smaller fidelity. By
computing teleportation fidelity, concurrence and purity for two-qubit
X-states, we show it explicitly. We further show that fidelity changes
monotonically with respect to functions of parameters - other than concurrence
and purity. A state with smaller concurrence and purity, but larger value of
one of these functions has larger fidelity. These functions, thus characterize
nonlocal classical and/or quantum properties of the state that are not captured
by purity and concurrence alone. In particular, concurrence is not enough to
characterize the entanglement properties of a two-qubit mixed state
Resource state structure for controlled quantum key distribution
Quantum entanglement plays a pivotal role in many communication protocols,
like secret sharing and quantum cryptography. We consider a scenario where more
than two parties are involved in a protocol and share a multipartite entangled
state. In particular, we considered the protocol of Controlled Quantum Key
Distribution (CoQKD), introduced in the Ref. Chin. Phys. Lett. 20, 183-185
(2003), where, two parties, Alice and Bob establish a key with the cooperation
of other parties. Other parties control/supervise whether Alice and Bob can
establish the key, its security and key rate. We discuss the case of three
parties in detail and find suitable resource states. We discuss the controlling
power of the third party, Charlie. We also examine the usefulness of the new
resource states for generating conference key and for cooperative
teleportation. We find that recently introduced Bell inequalities can be useful
to establish the security of the conference key. We also generalize the
scenario to more than three parties.Comment: 11 pages, 7 figures. Close to published versio
Effects of Phase Transition induced density fluctuations on pulsar dynamics
We show that density fluctuations during phase transitions in pulsar cores
may have non-trivial effects on pulsar timings, and may also possibly account
for glitches and anti-glitches. These density fluctuations invariably lead to
non-zero off-diagonal components of the moment of inertia, leading to transient
wobbling of star. Thus, accurate measurements of pulsar timing and intensity
modulations (from wobbling) may be used to identify the specific pattern of
density fluctuations, hence the particular phase transition, occurring inside
the pulsar core. Changes in quadrupole moment from rapidly evolving density
fluctuations during the transition, with very short time scales, may provide a
new source for gravitational waves.Comment: 9 pages, 1 figure. arXiv admin note: substantial text overlap with
arXiv:1412.427
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