1,253 research outputs found
Hunting for neutral, long-lived exotica at the LHC using a missing transverse energy signature
Searches at the Large Hadron Collider (LHC) for neutral, long-lived particles
have historically relied on the detection of displaced particles produced by
their decay the detector volume. In this paper we study the
potential of the complementary signature comprising of the missing transverse
energy () signal, traditionally used to look for dark matter, e.g.,
the lightest supersymmetric particle (LSP), to extend the LHC coverage to
models with long-lived (LL) particles when they decay the
detector. Using CMS and ATLAS analyses at the 8 TeV LHC, we set an upper limit
at the 95% confidence level (CL) on the production cross sections for two
specific scenarios: (i) a model with a heavy non-standard model Higgs boson
decaying to a LL scalar and (ii) an R-parity violating RPV SUSY model with a LL
neutralino.
We show that this method can significantly extend the LHC sensitivity to
neutral, LL particles with arbitrary large lifetimes and that the limits
obtained from a signal are comparable to those from displaced
particle searches for decay distances above a few meters. Results obtained in
this study do not not depend on the specific decay channel of the LL particle
and therefore are model-independent in this sense. We provide limits for the
whole two-dimensional plane in terms of the mass of the LL particle and the
mass of the mediator up to masses of 2 TeV including particular benchmarks
studied in the original experimental papers. We have made these limits
available in the form of a grid which can be used for the interpretation of
various other new physics models.Comment: 28 page
Analytic approximations to the phase diagram of the Jaynes-Cummings-Hubbard model with application to ion chains
We discuss analytic approximations to the ground state phase diagram of the
homogeneous Jaynes-Cummings-Hubbard (JCH) Hamiltonian with general short-range
hopping. The JCH model describes e.g. radial phonon excitations of a linear
chain of ions coupled to an external laser field tuned to the red motional
sideband with Coulomb mediated hopping or an array of high- coupled cavities
containing a two-level atom and photons. Specifically we consider the cases of
a linear array of coupled cavities and a linear ion chain. We derive
approximate analytic expressions for the boundaries between Mott-insulating and
superfluid phases and give explicit expressions for the critical value of the
hopping amplitude within the different approximation schemes. In the case of an
array of cavities, which is represented by the standard JCH model we compare
both approximations to numerical data from density-matrix renormalization group
(DMRG) calculations.Comment: 9 pages, 5 figures, extended and corrected second versio
BeitrÀge zur Totalsynthese von Lysolipin I
Die vorliegende Dissertation behandelt Studien zur Totalsynthese des SekundĂ€rmetabolits Lysolipin I (1), eines der höchst-oxidierten, aromatischen Polyketide. Der heptazyklische Kern dieses potenten Antibiotiukums beinhaltet sowohl eine Xanthon- (A-C), als auch eine Isochinolineinheit (F+G), welche ĂŒber ein zentrales Phenathrensystem (C-F) miteinander verbunden sind. Der siebte Ring (D) wird ĂŒber eine AcetalbrĂŒcke zwischen dem Xanthon und dem Phenanthrenkern gebildet. Lysolipin I (1) weist sowohl gegen gram-positive als auch gram-negative BakterienstĂ€mme biologische AktivitĂ€ten auf und hemmt das Wachstum verschiedener Tumorzelllinien. Im Unterschied zu frĂŒheren Versuchen der Totalsynthese dieses Naturstoffs wurde Lysolipin I (1) bei der Syntheseplanung in die zwei Hauptstrukturmerkmale zerlegt, das Isochinolin als SĂŒdfragment 211 und das Xanthon, als Nordfragment 212, welche ĂŒber eine flexible Kupplungsstrategie miteinander verknĂŒpft werden können. Die Synthese des SĂŒdfragments wird in der Dissertation von Thomas Voigt und in der kĂŒnftigen Dissertation von Maximilian Heinemann behandelt, wĂ€hrend der Hauptfokus im ersten Teil dieser Arbeit auf der Synthese des Nordfragments liegt. Es werden verschiedene kurze, variable Syntheserouten, ausgehend von kommerziell erhĂ€ltlichen Edukten, zum vorliegenden Xanthon 212 aufgezeigt. In einem zweiten Teil der Arbeit wird mit Studien zur VerknĂŒpfung der Hauptfragmente ĂŒber Sonogashira-Kupplungen die groĂe FlexibilitĂ€t der Syntheseplanung verdeutlicht, welche den Grundstein zur Synthese zahlreicher möglicher Analoga des Naturstoffs Lysolipin I (1) bilden.Contributions to the total synthesis of Lysolipin I
This thesis deals with studies towards the total synthesis of Lysolipin I (1). With its 11 oxygen atoms this polyketide is one of the highest oxidized secondary metabolites. Its heptacyclic aromatic core combines a xanthone (A-C) and an isoquinolinone subunit (F+G) which are condensed to a central phenanthrene system (C-F). The seventh ring (D) is built by an acetalbridge between the xanthone and the phenanthrene core. Lysolipin I exhibits potent biological activities against gram-positive and gram-negative bacteria. Furthermore, it also inhibits the growth of different tumor cell lines. As distinct from attempts for a total synthesis of this natural product in the past, Lysolipin I (1) was disconnected retrosynthetically in two structural moieties, the isochinolinone system as south- 211, and the xanthone as northfragment 212, which can be connected with a highly flexible coupling strategy. The synthesis of the southern fragment is discussed in the dissertation of Thomas Voigt and will be the topic of the dissertation of Maximilian Heinemann, while the main focus of this thesis is the synthesis of the northern fragment 212. Different short routes to yield the xanthone moiety from commercially available starting materials are presented. In a second part of the thesis studies towards the connection of the two main fragments via a Sonogashira-coupling illustrate maximum flexibility of the synthetic plan, which paves the way for a variety of potent analogs of the natural product Lysolipin I (1)
Infinite-dimensional port-Hamiltonian systems with a stationary interface
We consider two systems of two conservation laws that are defined on
complementary spatial intervals and coupled by an interface as a single
port-Hamiltonian system. In case of a fixed interface position, we characterize
the boundary and interface conditions for which the associated port-Hamiltonian
operator generates a contraction semigroup. Furthermore, we present sufficient
conditions for the exponential stability of the generated -semigroup. The
results are illustrated by the example of two acoustic waveguides coupled by an
interface consisting of some membrane.Comment: arXiv admin note: text overlap with arXiv:2301.0734
Bargain Hunting on Black Friday - Making Great Deals and Bragging About Them
Online customer reviews (OCRs) are helpful when they provide an unbiased view on a product. Large-scale shopping events (e.g., Black Friday) generate large volumes of OCRs. We hypothesize that OCRs from such events are biased due to price discounts and smart shopper feelings. To test our hypotheses, we use OCR data of a large US electronics retailer that emerge from Black Friday purchases and regular purchases. We find that numerical ratings from Black Friday purchases are considerably higher. This effect is also observable in an increase of the average numerical rating through Black Friday purchases. We further observe that textual OCR content from Black Friday purchases focuses more on the purchase conditions (e.g., price discounts) at the expense of other, potentially more helpful content. We further provide managerial implications on how retailers may counteract the negative consequences of such biased OCRs on the quality of their OCR systems
Scorzonera sensu lato (Asteraceae, Cichorieae) â taxonomic reassessment in the light of new molecular phylogenetic and carpological analyses
Scorzonera comprises 180â190 species and belongs to the subtribe Scorzonerinae. Its circumscription has long been the subject of debate and available molecular phylogenetic analyses affirmed the polyphyly of Scorzonera in its wide sense. We provide a re-evaluation of Scorzonera and other related genera, based on carpological (including anatomical) and extended molecular phylogenetic analyses. We present, for the first time, a comprehensive sampling, including Scorzonera in its widest sense and all other genera recognised in the Scorzonerinae. We conducted phylogenetic analyses using Maximum Parsimony, Maximum Likelihood and Bayesian analyses, based on sequences of the nuclear ribosomal ITS and of two plastid markers (partial rbcL and matK) and Maximum Parsimony for reconstructing the carpological character states at ancestral nodes. Achene characters, especially related to pericarp anatomy, such as general topography of the tissue types, disposition of the mechanical tissue and direction of its fibres, presence or absence of air cavities, provide, in certain cases, support for the phylogenetic lineages revealed. Confirming the polyphyly of Scorzonera, we propose a revised classification of the subtribe, accepting the genera Scorzonera (including four major clades: Scorzonera s. str., S. purpurea, S. albicaulis and Podospermum), Gelasia, Lipschitzia gen. nov. (for the Scorzonera divaricata clade), Pseudopodospermum, Pterachaenia (also including Scorzonera codringtonii), Ramaliella gen. nov. (for the S. polyclada clade) and Takhtajaniantha. A key to the revised genera and a characterisation of the genera and major clades are provided
Tell Me Why (I Want It That Way) â Effects of Explanations and Online Customer Reviews on Trust in Recommender Systems
Review-based recommender systems (RS) have shown great potential in helping users manage information overload and find suitable items. However, a lack of trust still impedes the widespread acceptance of RS. To increase usersâ trust, research proposes various methods to generate justifications or explanations. Furthermore, online customer reviews (OCRs) are found to be a trustworthy and reliable source of information. However, it is still unclear how justifications compare to explanations in their influence on usersâ trust and whether basing them on OCRs additionally adds trust. Hence, we conduct an online experiment with 531 participants and find that explanations exceed justifications in increasing usersâ trust, while basing them on OCRs directly increases usersâ intentions to use the system and adopt recommendations without increasing trust in the RS themselves. Unifying different research streams from review-based RS and Explainable Artificial Intelligence, we provide an overarching, holistic view on the conception of justifications and explanations
Dynamic Pricing on Two-Sided Platforms: Consequences on Customersâ Fairness Perceptions and Purchase Intentions
Technological advancements simplify the application of dynamic pricing, i.e., the flexible and rapid adjustment of prices to changes in demand. Consequently, companies increasingly use dynamic pricing in their business models, although research reports negative consequences on customer fairness perceptions. This holds not only for one-sided businesses, but also for popular two-sided platforms. However, these platforms differ from one-sided businesses in that the total prices paid by customers consist of product prices and platform fees â and both price components can be dynamically adjusted. In an online experiment, we examine customersâ fairness perceptions and purchase intentions when product price and platform fee change dynamically. We find that dynamic price increases reduce fairness perceptions and purchase intentions, while the cause of the price increases is irrelevant to customers. These results indicate an imbalance in the risks and benefits of dynamic pricing between the pricing strategies of the platform and the provider
Persistence problems for fractional processes
In this thesis, we deal with several persistence problems for fractional processes. Persistence concerns the event that a stochastic process has a long excursion staying below or above a certain barrier. A central question in this context is the analysis of the probability of this event - the so-called persistence probability.
We first consider the persistence probabilities of integrated fractional Brownian motion and fractionally integrated Brownian motion. While it is well-known that these persistence probabilities decay asymptotically polynomially, their polynomial rates are unknown except for the special cases of Brownian motion and integrated Brownian motion. We show that for both processes, the polynomial rate is a continuous function in the Hurst parameter and determine its asymptotic behaviour at the boundaries of the respective parameter domain.
Subsequently, we study persistence probabilities of mixed processes, such as mixed fractional Brownian motion. Precisely, we consider the sum of two self-similar centred Gaussian processes with different self-similarity indices and show that, under non-negativity assumptions of covariance functions and some further minor conditions, the persistence probability of the sum decays asymptotically polynomially with the same polynomial rate as for the single process with the greater self-similarity index. In particular, this determines the polynomial rate of the persistence probability of mixed fractional Brownian motion.
Lastly, we give estimates for the persistence probabilities of further fractional processes of interest, namely the bifractional Brownian motion and the fractional Ornstein-Uhlenbeck process
Lead-free, luminescent perovskite nanocrystals obtained through ambient condition synthesis
Heterovalent substitution of toxic lead is an increasingly popular design
strategy to obtain environmentally sustainable variants of the exciting
material class of halide perovskites. Perovskite nanocrystals (NCs) obtained
through solution-based methods exhibit exceedingly high optical quality.
Unfortunately, most of these synthesis routes still require reaction under
inert gas and at very high temperatures. Herein we present a novel synthesis
routine for lead-free double perovskite NCs. We combine hot injection and
ligand-assisted reprecipitation (LARP) methods to achieve a low-temperature and
ambient atmosphere-based synthesis for manganese-doped Cs_{2}NaBiCl_{6} NCs. Mn
incorporation is critical for the otherwise non-emissive material, with a 9:1
Bi:Mn precursor ratio maximizing the bright orange photoluminescence (PL) and
quantum yield (QY). Higher temperatures slightly increased the material's
performance, yet NCs synthesized at room temperature were still emissive,
highlighting the versatility of the synthetic approach. Furthermore, the NCs
show excellent long-term stability in ambient conditions, facilitating
additional investigations and energy-related applications
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