Elliptische Galaxien: Umgebung, Struktur und stellare Population (German Edition)
T h e Cosmic Perspective: The sunlight method, 7th variation includes Chapters 1—13, The Cosmic point of view: Very Massive Stars in the Local Universe Astrophysics and - download pdf or read online This booklet provides the prestige of study on very giant stars within the Universe. Making a Success of Astronomical PDF Beginner astronomers who've been disillusioned through the result of an watching consultation can take convenience within the information of this ebook, which advises tips to nonetheless achieve worthwhile event in doubtless "failed" nights on the telescope.
Download e-book for kindle: The most abundant UV-induced photo-lesions result from the formation of a cyclobutane ring between adjacent thymine bases CPD-lesions. Although the formation of these thymine dimers has been reported in the early s, until now neither the time scale of dimer formation nor the reaction mechanism has been resolved. The focus of this work is on the investigation of photophysical and photochemical processes in nucleic acids on the picosecond time scale.
Pump-probe spectroscopy allows the investigation of ultrafast, photo-induced processes. The applied spectrometer is based on a central femtosecond laser system. The emitted short light pulses nm, 90 fs are converted via nonlinear processes into the required spectral regions ultraviolet pump: In this way the high-structure sensitivity of vibrational spectroscopy can be combined with a time resolution in the sub picosecond regime. For the investigation of thymine dimer formation, two thymine derivatives were chosen: Additional experiments were performed on the all-adenine single strand poly A and the mononucleotide adenine-5'-monophosphate, as adenine is the complementary base of thymine in the DNA double helix.
While in AMP virtually all excited adenine bases return to the vibrationally excited ground state via a fast, internal conversion 1 ps , there is an additional population of long-lived, electronic states in poly A , with lifetimes in the ps- and ns-regime. The population of these states correlates with the amount of stacked bases in poly A.
This can be explained by the formation of excimer states. The IR absorption of these states could be deduced in this paper for the first time. To resolve the UV-induced formation of CPD-lesions, the characteristic IR absorption of thymine dimers was determined from stationary irradiation experiments on dT Long-lived electronic states ps - 1 ns do not lead to dimer formation. Therefore, the photoreaction can only take place if the conformation of two bases at the moment of UV absorption is already suitable for dimerization.
This interpretation can be transferred to the DNA double helix, in which deviations from the ideal helix structure are necessary for dimer formation. In this work a fundamental question of photochemical reactions in DNA is resolved, which is of central importance to the understanding of the frequency of damage and mutation patterns in the genome. Clean Plasmonische Nahfeldresonatoren aus zwei biokonjugierten Goldnanopartikeln. Clean Spectroscopy of high-Z ions as a way to understanding the nature of Cas A knots and intergalactic shocks.
Clean Alte Photoreaktionen in neuem Licht. The scope of the work presented is the investigation of photochemical reactions by means of ultrafast spectroscopy. Naturally these reactions start off in an optically bright excited state. Femtosecond time-resolved fluorescence spectroscopy is thus the method of choice to track the spectral and temporal dynamics of these emissive states.
Here, an ultrafast fluorescence spectrometer based on the optical Kerr-effect serves as the appropriate tool to pursue this task. Additional information on dark states and ground states is provided by Uv-Vis transient absorption experiments. The first part of the thesis deals with a fundamental concept of mechanistic chemistry — the pericyclic reactions. The spectroscopic consequences implied within this theoretical framework are investigated by means of emission and absorption spectroscopy. The molecular probe is an indolyl-substituted fulgimide which undergoes a light-induced cyclization or cycloreversion, respectively.
Both reactions feature a bi-phasic emission decay cyclization: The large difference in the slower time constants as well as the spectral properties of the corresponding emission point to the existence of different excited state pathways for both reactions. These results challenge the basic one-dimensional reaction scheme commonly used to describe pericyclic reactions. Referring to theoretical investigations, a two-dimensional reactive space is proposed to hold responsible for the different behaviour of the two isomers.
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The second part of the studies focuses on the dynamics of a certain type of photolabile protecting groups. These molecules are intramolecularly sensitised by a triplet energy donor, namely thioxanthone, and feature an ortho-substituted nitroaromatic as the reactive core. These results can be directly transferred to thioxanthone and the sensitised protecting groups. Finally, the photo-reactive ortho-nitrobenzaldehyde o-NBA is compared with its non-reactive isomers m- and p-NBA as model systems to obtain information on the reactive core of the protecting groups.
Clean Elektrooptische und elektromechanische Charakterisierung von Carbon Nanotubes. Clean Genetic switching into the competent state. Near the end of their evolution, moderate-mass stars approximatively between 1 and 8 solar masses go through the asymptotic giant branch AGB phase. Hence, large grids of models originating from detailed calculations are rare; only few stars are generally computed.
Some stellar libraries have nonetheless been constituted in the past. These are very sought-after by population synthesis modelers, as they try to reproduce observed properties of larger stellar systems by assembling together many individual models. So-called synthetic AGB models are a solution as they are computationally less time demanding: In this context, new detailed models for stars of 1 to 6 solar masses, and compositions with a total heavy element content that corresponds to values between a fortieth and a double of the solar one for two different relative scalings , have been computed.
They evolve through all stellar phases from the main sequence to the white dwarf stage; here focus is on the AGB and post-AGB parts. These updates, at the level of sophistication brought by this work, are present neither in synthetic nor in any detailed computations. Because they are of paramount importance, their inclusion is the major asset of this work.
Specifically, three updates have been implemented: With overshooting, envelope mixing will be more efficient and dredge-up additional material from deeper layers. The stellar surface will thus be converted from an oxygen- to a carbon-rich one, and changes will directly affect the opacities and in turn the mass-loss rates. While ignored in previous models, these transformations are now taken into account.
We show, how such amendments were a necessity by comparing the results with older grids, and how models are in agreement, without any prior calibration, with observations. The AGB tracks cover the entire parameter space. Post-AGB models are also available for the full metallicity range but, because of convergence issues, only for star between 1 and 2 solar masses.
To our knowledge this work provides the scientific community with the most up-to-date, self-consistent and extended grid, originating from detailed AGB and post-AGB models. It is expected to be a valuable input-tool for population synthesis work and aims to supersede the more than year old outdated tracks that are currently still being used.
Clean Dynamic patterns of biological systems. Clean Dissociation properties of biomolecules under an externally applied force. Clean Ray-Tracing through the Millennium Simulation. In this thesis, gravitational lensing in the concordance LambdaCDM cosmology is investigated by carrying out ray-tracing along past light cones through the Millennium Simulation, a very large N-body simulation of cosmic structure formation.
The method used for tracing light rays substantially extends previous ray-tracing methods that are based on the Multiple-Lens-Plane approximation. Strong lensing is investigated by shooting random light rays through the Millennium Simulation. The probability is evaluated that an image of a small distant light source will be highly magnified, will be highly elongated or will be one of a set of multiple images. It is found that these probabilities increase strongly with increasing source redshift.
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It is shown that strong-lensing events can almost always be traced to a single dominant lensing object, and the mass and redshift distribution of these primary lenses is studied. The observed lens-mass range extends to lower masses than those found in earlier studies using simulations with lower spatial and mass resolution.
Furthermore, effects of additional material along the line-of-sight are investigated. Although strong-lensing lines-of-sight are indeed biased towards higher than average mean densities, this additional matter typically contributes only a few percent of the total surface density. The influence of stellar mass in galaxies on strong lensing is investigated by comparing the results obtained for lensing by dark matter alone to those obtained by also including the luminous matter. The dark-matter component of the lensing matter is constructed directly from the dark-matter particle distribution of the Millennium Simulation, while the luminous component is inferred from semi-analytic galaxy-formation models implemented within the evolving dark-matter distribution of the simulation.
It is found that the inclusion of the stellar mass strongly enhances the probability for strong lensing compared to a 'dark-matter only' universe. The identification of the lenses associated with strong-lensing events reveals that the stellar mass of galaxies i significantly enhances the strong-lensing cross-sections of group and cluster halos, and ii gives rise to strong lensing in smaller halos, which would not produce noticeable effects in the absence of the stars. Finally, the potential capabilities of future radio telescopes for imaging the cosmic matter distribution are discussed.
The Millennium Simulation is used to simulate large-area maps of the lensing convergence with the noise, resolution and redshift-weighting achievable with a variety of idealised surveys. It is shown that by observing lensing of cm emission during reionization with a sufficiently large radio telescope, an image of the matter distribution could be obtained whose signal-to-noise far exceeds that of any map made using galaxy lensing.
These mass images would allow the dark-matter halos of individual galaxies to be viewed directly, giving a wealth of statistical and morphological information about the relative distributions of mass and light. For telescopes like the planned Square Kilometre Array, mass imaging may be possible near the resolution limit of the core array of the telescope. Clean Coherent manipulation of ultracold atoms on atom chips.
Blazars, a subclass of active galactic nuclei in which the jet is aligned very close to our line of sight, can accelerate charged particles to relativistic energies in the jet. Electromagnetic emission from this class of sources can be observed from radio up to TeV energies. A VHE gamma-ray signal was discovered with a 5. On the other hand, the data showed no significant excess. This drop in flux followed the observed trend in the optical activity. For the first time, the VHE gamma-ray spectra were simultaneously obtained with the X-ray spectra during their low states of activity.
Long term observations of Mkn in showed a strong variability in VHE gamma-ray emission. The spectral energy distributions SEDs of these four blazars could be well explained by a homogeneous one-zone synchrotron self-Compton model. This model suggests that the variation of the injected electron population in the jet is responsible for observed variations of the SEDs of the blazars. For all sources, the derived magnetic field strength in the jet and the Doppler beaming factor showed similar values.
A contribution on the hardware sector is also presented in this thesis. Other performance values including lifetime also fulfilled the requirements of photosensors to be used in the MAGIC telescope. It is shown that laser cooling at high beam energies is feasible and that momentum spreads much smaller than those observed for electron cooling can be achieved.
Resulty indicate that space-charge dominated beams have been observed, reaching the regime of strong coupling which is an essential prerequisite for beam crystallization. Moderate electron cooling was employed to create three-dimensionally cold beams. With the laser cooled beams it was possible to perform precision VUV spectroscopy of the cooling transition. It is shown that cooling times short enough for cooling unstable nuclei can be achieved and fast recooling of the plasma is possible. With this cooling scheme highly charged ions for precision experiments such as mass spectrometry in Penning traps at millikelvin temperatures can be delivered.
Clean Ultrakurzzeitspektroskopie von Hemithioindigo und biophysikalisch relevanten Derivaten. Die photochrome Verbindung Hemithioindigo isomerisiert im Pikosekundenzeitbereich. Die vorliegende Arbeit behandelt dabei die folgenden Fragestellungen: Es wird gezeigt, dass die Reaktionsraten der photoinduzierten Isomerisierungen durch Potentialbarrieren im elektronisch angeregten Zustand bestimmt werden. Die Auswirkungen der Substituenten-Effekte auf unterschiedliche Parameter werden diskutiert und in ein gemeinsames Reaktionsmodell eingebettet. Welcher Bestandteil dominiert die dynamischen Eigenschaften von Hemithioindigo?
Hemithioindigo stellt somit eine vielversprechende Alternative zu bekannten molekularen Schaltern, wie z. Clean Plasma-Neutralgas-Wechselwirkung im interstellaren Medium. Clean Kontrolle des Energietransfers in hybriden und pi-konjugierten Systemen. Clean Radiatively-driven processes in forest fire and desert dust plumes. The absorption of solar radiation by atmospheric aerosol particles is important for the climate effects of aerosols. Absorption by aerosol particles heats atmospheric layers, even though the net effect for the entire atmospheric column may still be a cooling.
Most experimental studies on absorbing aerosols so far focussed mainly on the aerosol properties and did not consider the influence of the aerosols on the thermodynamic structure of the atmosphere. The experimental data are used to explore the impact of layers containing absorbing forest fire and desert dust aerosol particles on the atmospheric stability and the implications of a changed stability on the development of the aerosol microphysical and optical properties during long-range transport. For the first time, vertical profiles of the Richardson number Ri are used to assess the stability and mixing in forest fire and desert dust plumes.
Also for the first time, the conclusions drawn from the observations of forest fire and desert dust aerosol, at first glance apparently quite different aerosol types, are discussed from a common perspective. Two mechanisms, the self-stabilising and the sealed ageing effect, acting in both forest fire and desert dust aerosol layers, are proposed to explain the characteristic temperature structure as well as the aerosol properties observed in lofted forest fire and desert dust plumes. The proposed effects impact on the ageing of particles within the plumes and reduce the plume dilution, therefore extending the plume lifetime.
This study combines experimental data, modelling of optical parameters and calculated heating rates to assess the role of forest fire and desert dust plumes. Aerosol size information and absorption data were analysed with respect to the aerosol mixing state, effective diameter and parameterisation of forest fire and dust size distributions.
Altogether, about 90 size distributions for particles from different sources were extracted from multiple instruments and parameterised with multi-modal log-normal distributions. Subsequently, the optical properties were calculated for the different aerosol layers and compared with other independent measurements of the optical properties like the extinction coefficient determined with a High Spectral Resolution Lidar. The aerosol optical properties serve as the basis for the radiative transfer calculations with libRadtran library for radiative transfer. Finally, the aerosol microphysical and optical properties, the meteorological data and the heating rates are examined to investigate the proposed self-stabilising and sealed ageing effects.
The investigation of numerous forest fire and desert dust plumes in this study revealed characteristic aerosol properties: The desert dust aerosol exhibits two size regimes of different mixing states: The cosmic origin and evolution is encoded in the large-scale matter distribution observed in astronomical surveys. Galaxy redshift surveys have become in the recent years one of the best probes for cosmic large-scale structures.
They are complementary to other information sources like the cosmic microwave background, since they trace a different epoch of the Universe, the time after reionization at which the Universe became transparent, covering about the last twelve billion years.
Regarding that the Universe is about thirteen billion years old, galaxy surveys cover a huge range of time, even if the sensitivity limitations of the detectors do not permit to reach the furthermost sources in the transparent Universe. This makes galaxy surveys extremely interesting for cosmological evolution studies.
The observables, galaxy position in the sky, galaxy ma gnitude and redshift, however, give an incomplete representation of the real structures in the Universe, not only due to the limitations and uncertainties in the measurements, but also due to their biased nature. They trace the underlying continuous dark matter field only partially being a discrete sample of the luminous baryonic distribution.
In addition, galaxy catalogues are plagued by many complications. Some have a physical foundation, as mentioned before, others are due to the observation process. The problem of reconstructing the underlying density field, which permits to make cosmological studies, thus requires a statistical approach. This thesis describes a cosmic cartography project. The necessary concepts, mathematical frame-work, and numerical algorithms are thoroughly analyzed.
On that basis a Bayesian software tool is implemented.
The resulting Argo-code allows to investigate the characteristics of the large-scale cosmological structure with unprecedented accuracy and flexibility. This is achieved by jointly estimating the large-scale density along with a variety of other parameters such as the cosmic flow, the small-scale peculiar velocity field, and the power-spectrum from the information provided by galaxy redshift surveys. Furthermore, Argo is capable of dealing with many observational issues like mask-effects, galaxy selection criteria, blurring and noise in a very efficient implementation of an operator based formalism which was carefully derived for this purpose.
Thanks to the achieved high efficiency of Argo the application of iterative sampling algorithms based on Markov Chain Monte Carlo is now possible. This will ultimately lead to a full description of the matter distribution with all its relevant parameters like velocities, power spectra, galaxy bias, etc. Some applications are shown, in which such techniques are used. A rejection sampling scheme is successfully applied to correct for the observational redshift-distortions effect which is especially severe in regimes of non-linear structure formation, causing the so-called finger-of-god effect.
Also a Gibbs-sampling algorithm for power-spectrum determination is presented and some preliminary results are shown in which the correct level and shape of the power-spectrum is recovered solely from the data. We present in an additional appendix the gravitational collapse and subsequent neutrino-driven explosion of the low-mass end of stars that undergo core-collapse Supernovae.
We obtain results which are for the first time compatible with the Crab Nebula. Clean Efficient generation of photonic entanglement and multiparty quantum communication. Entangled photons are at the heart of experimental quantum physics. They were used for the first fundamental tests of quantum theory, and became a basic building block for many novel quantum protocols, such as quantum cryptography, dense coding or teleportation.
Therefore, the efficient generation of entangled photons, as well as their distribution and accurate analysis are of paramount importance, particularly with regard to the practicability of many applications of quantum communication. This thesis deals largely with the problem of efficient generation of photonic entanglement with the principal aim of developing a bright source of polarization-entangled photon pairs, which meets the requirements for reliable and economic operation of quantum communication prototypes and demonstrators.
Our approach uses a correlated photon-pair emission in nonlinear process of spontaneous parametric down-conversion pumped by light coming from a compact and cheap blue laser diode. Two alternative source configurations are examined within the thesis. The first makes use of a well established concept of degenerate non-collinear emission from a single type-II nonlinear crystal and the second relies on a novel method where the emissions from two adjacent type-I phase-matched nonlinear crystals operated in collinear non-degenerate regime are coherently overlapped.
This performance, together with the almost free of alignment operation of the system, suggest that it is an especially promising candidate for many future practical applications, including quantum cryptography, detector calibration or use in undergraduate lab courses. The second issue addressed within the thesis is the simplification and practical implementation of quantum-assisted solutions to multiparty communication tasks. While the recent rapid progress in the development of bright entangled photon-pair sources has been followed with ample experimental reports on two-party quantum communication tasks, the practical implementations of tasks for more than two parties have been held back, so far.
This is mainly due to the requirement of multiparty entangled states, which are very difficult to be produced with current methods and moreover suffer from a high noise. We show that entanglement is not the only non-classical resource endowing the quantum multiparty information processing its power. Instead, only the sequential communication and transformation of a single qubit can be sufficient to accomplish certain tasks.
This we prove for two distinct communication tasks, secret sharing and communication complexity. Whereas the goal of the first is to split a cryptographic key among several parties in a way that its reconstruction requires their collaboration, the latter aims at reducing the amount of communication during distributed computational tasks.
Importantly, our qubit-assisted solutions to the problems are feasible with state-of-the-art technology. This we clearly demonstrate in the laboratory implementation for 6 and 5 parties, respectively, which is to the best of our knowledge the highest number of actively performing parties in a quantum protocol ever implemented. Thus, by successfully solving and implementing a cryptographic task as well as a task originating in computer science, we clearly illustrate the potential to introduce multiparty communication problems into real life.
Auch diese Aspekte werden hier dokumentiert und die erreichten Fortschritte aufgezeigt siehe hierzu Kapitel 2. Clean Long distance free-space quantum key distribution. In the age of information and globalisation, secure communication as well as the protection of sensitive data against unauthorised access are of utmost importance. Quantum cryptography currently provides the only way to exchange a cryptographic key between two parties in an unconditionally secure fashion.
Owing to losses and noise of today's optical fibre and detector technology, at present quantum cryptography is limited to distances below a few km. In principle, larger distances could be subdivided into shorter segments, but the required quantum repeaters are still beyond current technology.
An alternative approach for bridging larger distances is a satellite-based system, that would enable secret key exchange between two arbitrary points on the globe using free-space optical communication. The aim of the presented experiment was to investigate the feasibility of satellite-based global quantum key distribution. In this context, a free-space quantum key distribution experiment over a real distance of km was performed.
The transmitter and the receiver were situated in m altitude on the Canary Islands of La Palma and Tenerife, respectively. The small and compact transmitter unit generated attenuated laser pulses, that were sent to the receiver via a cm optical telescope. The receiver unit for polarisation analysis and detection of the sent pulses was integrated into an existing mirror telescope designed for classical optical satellite communications.
To ensure the required stability and efficiency of the optical link in the presence of atmospheric turbulence, the two telescopes were equipped with a bi-directional automatic tracking system. Still, due to stray light and high optical attenuation, secure key exchange would not be possible using attenuated pulses in connection with the standard BB84 protocol.
The photon number statistics of attenuated pulses follows a Poissonian distribution. Hence, by removing a photon from all pulses containing two or more photons, an eavesdropper could measure its polarisation without disturbing the polarisation state of the remaining pulse. In this way, he can gain information about the key without introducing detectable errors.
To protect against such attacks, the presented experiment employed the recently developed method of using additional "decoy" states, i. By analysing the detection probabilities of the different pulses individually, a photon-number-splitting attack can be detected. Thanks to the decoy-state analysis, the secrecy of the resulting quantum key could be ensured despite the Poissonian nature of the emitted pulses.
Our outdoor experiment was carried out under real atmospheric conditions and with a channel attenuation comparable to an optical link from ground to a satellite in low earth orbit. Hence, it definitely shows the feasibility of satellite-based quantum key distribution using a technologically comparatively simple system.
Die Messergebnisse deuten auf einem Modell mit einer direkten photochemischen Umwandlung auf der Zeitskala von wenigen Pikosekunden und ohne langlebige Intermediate hin. The topic of this thesis is the correspondence of open and closed strings. Already for a long time it has been evident that those both sectors of string theory do not only couple to each other, but it is also possible to identify excitations of the closed string in the open string sector.
This correspondence has been shown in a multitude of examples, which indicates a deep connection. In this work we consider different aspects of k-essence theories, which are scalar field theories described by the generally covariant and Lorentz invariant action with non-canonical kinetic terms. It is shown that, because of the intrinsic nonlinearity, these theories can have rather unexpected and unusual physical properties. As in the usual relativistic field theories, any nontrivial dynamical solution of the k-essence equation of motion spontaneously breaks the Lorentz invariance.
Thus the perturbations around such solutions propagate in a "new aether". In contrast to the usual relativistic field theories, these perturbations propagate in an "effective" metric which is different from the usual gravitational metric. This effective metric can be interpreted as the so-called "emergent spacetime". In this thesis we show that the dynamics of the perturbations can be described by the action which is generally covariant with respect to the reparameterization of this "emergent spacetime".
The most interesting manifestation of this "emergent spacetime" is that perturbations can propagate faster than light. We show that despite the superluminal propagation the causal paradoxes do not arise in these theories, and in this respect these theories are not less safe than General Relativity. This superluminal propagation of perturbations has interesting consequences for cosmology and black hole physics. In particular, it is possible to construct models of inflation with an enhanced production of gravitational waves.
Moreover, we have shown that there exist k-essence models which in principle allow to obtain information from the region beyond the black hole horizon. This information is encoded in the perturbations around the solution describing the stationary accretion of the k-essence onto the black hole. We have shown that in the framework of general k-essence the dynamical violation of NEC is physically implausible.
Clean Interaction of particles with complex electrostatic structures and 3D clusters. Particles of micrometer size externally introduced in plasmas usually find their positions of levitation in the plasma sheath, where the gravity force is compensated by the strong electric field. Here due to electrostatic interaction they form different structures, which are interesting objects for the investigation of strongly coupled systems and critical phenomena. Because of the low damping e.
Einstein frequency at the most elementary level of single particle motion. The task of this work was to analyze the three dimensional structure, dynamical processes and the limit of the cooperative behavior in small plasma crystals. In addition to the study of the systems formed, the immersed particles themselves may be used for diagnostics of the plasma environment: The laboratory experiments are performed in two radio-frequency RF plasma reactors with parallel plate electrodes, where the lower electrode is a so-called "adaptive electrode". When RF voltage is applied to one of these pixels, a bright localized glow, "secondary plasma ball", appears above.
Three dimensional dust crystals with less than particles are formed inside this "plasma ball" - the ideal conditions for the investigation of the transition from cluster systems to collective systems. The investigation of the particle interactions in crystals is performed with an optical diagnostic, which allows determination of all three particle coordinates simultaneously with time resolution of 0. The experimental results are: The binary interaction among particles in addition to the repelling Coulomb force exhibits also an attractive part, which is experimentally determined for the first time.
Analysis of the dynamical evolution shows the tendency of the systems to approach the state with minimum energy by rearranging particles inside. The measured 63 particles' crystal vibrations are in close agreement with vibrations of a drop with surface tension. This indicates that even a 63 particle crystal already exhibits properties normally associated with the cooperative regime.
The possibility to use levitated particles as a new powerful diagnostic of the plasma sheath region is proposed. The existence of different equilibrium positions of microparticles suspended in an Oxygen discharge provides evidence of a structured electronegative plasma sheath, a feature so far only mathematically and numerically investigated. Furthermore, the new Z-H red sequence method has allowed a cluster sample study over an unprecedented redshift baseline of 0. This confirms the well-established old age of the stellar populations of early-type galaxies in clusters.
My tentative finding that nearby BCGs have old, passively evolving stellar populations and were assembled in the last 9Gyr is in qualitative agreement with predictions from the latest numerical simulations based on the standard cold dark matter scenario of galaxy formation and evolution via hierarchical merging. The confirmation and refinement of these preliminary results will contribute to the development of a consistent picture of the cosmic evolution of galaxy populations and the large-scale structure. Clean Experiments on Multiphoton Entanglement.
Entanglement lies at the heart of quantum mechanics and challenged the intuition of physicists ever since it was discovered. At the same time, it is a powerful tool that serves as a key resource for quantum communication and quantum computation schemes. Many of these applications rely on multiparticle entanglement, whose description, generation and manipulation became therefore a very active field in theoretical and experimental quantum information science.
The goals are here to classify and understand the different types of entanglement, to find new applications and to control and analyze the quantum states experimentally. In this thesis, the experimental observation and analysis of two different types of four-photon polarization entangled states is presented: The cluster state and the symmetric Dicke state with two excitations. For this purpose, experimental setups based on spontaneous parametric down conversion and linear optics with conditional detection were designed. They allowed to observe the cluster state with a fidelity of The cluster state experiment included the development of a new instrument that is of interest for linear optics quantum logic in general: A probabilistic controlled phase gate that is, due to the simplification of a previous approach, highly stable and can actually be used in multiphoton experiments.
The quality of the gate is evaluated by analyzing its entangling capability and by performing full process tomography. The achieved results demonstrate that this device is well suited for implementation in various multiphoton quantum information protocols.
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In order to study the observed quantum states, efficient analysis tools are introduced. It was possible to verify that essential properties of the ideal states are indeed reproduced in the experiment, among others, the presence of genuine four-partite entanglement. A particular focus is put on the behavior of the states under projective measurements and photon loss. Several new insights in their entanglement structure are revealed and verified experimentally.
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