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Number of Titles Found: 75
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| Title: A Design Approach for Adsorption Energy Systems Integrating Dynamic Modeling with Small-Scale Experiments |
| Series: Aachener Beiträge zur Technischen Thermodynamik |
| By (author): Stefan Wilhelm Graf |
| ISBN10-13: 3958862586 : 9783958862586 |
| Adsorption energy systems can be driven by thermal energy from waste heat or the sun and thereby allow reducing fossil energy consumption and thus reduce global greenhouse gas emissions. Adsorption heat pumps and chillers can provide heating or cooling, adsorption thermal energy storage allows storing thermal energy. However, adsorption energy systems suffer from high investment costs due to low performance. Performance of adsorption energy systems strongly depends on the equilibrium properties of the working pair as well as heat and mass transfer mechanisms of the adsorption material in the adsorption energy system (adsorbent configuration). Evaluating new working pairs and adsorbent configurations is rather challenging: While the working pair's equilibrium properties can be determined with standardized measurement equipment, heat and mass transfer mechanisms cannot easily be determined, since they strongly depend on the full-scale adsorption energy system. Construction and operation of full-scale experiments requires high effort. Besides, often only small amounts of an adsorbent configuration are available, which are insufficient for full-scale experiments. To resolve these drawbacks, this thesis provides and validates a comprehensive method to determine the performance of working pairs and adsorbent configurations in adsorption energy systems from simple small-scale experiments. As a representative class of adsorption energy systems, adsorption chillers are investigated in this thesis. A small-scale Large-Temperature-Jump experiment is combined with dynamic modeling of the transient heat and mass transfer processes. Additionally, the experiment is extended by an infrared camera. The additional temperature information allows to distinguish and to determine the time-resolved effective heat transfer coefficient and diffusion coefficient in the heat and mass transfer model. The heat transfer and diffusion coefficients are inserted into a full-scale adsorption chiller model to predict the performance. Exemplarily, a commercial available silica gel and the adsorbent class of metal-organic frameworks (MOFs) are evaluated for an adsorption chiller application. The method is validated with experimental data of a full-scale prototype adsorption chiller and shows high accuracy. Furthermore, the method allows optimizing the adsorption chiller for a given working pair or adsorbent configuration and allows identifying bottlenecks and potential for improvement of the working pairs. In summary, this thesis bridges the gap between small-scale experiments and modeling of full-scale adsorption energy systems. The method allows for a comprehensive and reliable evaluation of working pairs and adsorbent configurations for adsorption energy systems. |
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Pages: 200
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| Published: Verlag G. Mainz - December 2018 |
| Format: Paperback |
| Subjects: |
| List Price: 43.99 Pounds Sterling |
| Availability: Temporarily Out of Stock, more expected soon |
| Title: 1 of: 75 |
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| Title: A Milliliter-Scale Setup for the Efficient Characterization of Multicomponent Vapor-Liquid Equilibria Using Raman Spectroscopy |
| Series: Technology in a Globalizing World |
| By (author): Bastian Liebergesell |
| ISBN10-13: 3958862470 : 9783958862470 |
| Vapor-liquid equilibrium (VLE) data are of major importance for the chemical industry. Despite significant progress in predictive methods, experimental VLE data are still indispensable. In this work, we address the need for experimental VLE data. Commonly, the characterization of VLE requires significant experimental effort. To limit the experimental effort, VLE measurements are frequently conducted by synthetic methods which employ samples of known composition and avoid complex analytics and sampling issues. In contrast, analytical methods provide independent information on phase compositions, commonly based on sampling and large amounts of substance. In the first part of this work, we employ a synthetic method, the well-established Cailletet setup, to characterize the high pressure VLE of two promising binary biofuel blends. The Cailletet method serves as a state of the art reference method that enables collecting data of remarkable accuracy. However, extensive infrastructure is needed. In the second part, to avoid extensive infrastructure and overcome limitations of previous methods, we develop a novel analytical milliliter-scale setup for the noninvasive and efficient characterization of VLE: RAMSPEQU (Raman Spectroscopic Phase Equilibrium Characterization). The novel setup saves substance and rapidly characterizes VLE. Sampling and its associated errors are avoided by analyzing phase compositions using Raman spectroscopy. Thereby, volumes of less than 3 ml are sufficient for reliable phase equilibrium measurements. To enable rapid data generation and save substance, we design an integrated workow combining Raman signal calibration and VLE measurement. As a result, RAMSPEQU gives access to up to 15 pT xy-data sets per workday. RAMSPEQU is successfully validated against pure component and binary VLE data from literature. However, mixtures with only two components rarely depict real industrial applications. As the number of experiments increases strongly with a rising number of components, the efficient RAMSPEQU setup seems particularly suited for multicomponent systems. In the third part of this work, we employ the RAMSPEQU setup for the characterization of a quaternary system and its binary subsystems. 22 ml and 105 ml of the binary and quaternary mixtures are sufficient for an extensive VLE characterization. The RAMSPEQU setup and its integrated workow enable the characterization of multicomponent VLE while saving significant amounts of substance and laboratory time. |
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Pages: 102
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| Published: Verlag G. Mainz - November 2018 |
| Format: Paperback |
| Subjects: |
| List Price: 43.99 Pounds Sterling |
| Availability: In Stock
Qty Available: 1 |
| Title: 2 of: 75 |
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| Title: A Model-based Framework for Optimal Systems Integration of Adsorption Chillers |
| Series: Aachener Beiträge zur Technischen Thermodynamik |
| By (author): Andrej Gibelhaus |
| ISBN10-13: 3958864066 : 9783958864061 |
| The global demand for cooling increases and poses a challenge for the stability of electrical grids and the emission targets. Thermally-driven adsorption chillers can meet this challenge by substituting electricity with thermal energy. However, although adsorption chillers are primarily driven by thermal energy, practical experience shows that the electricity savings often hardly compensate the electricity demand of the auxiliaries, such as pumps and fans. Thus, smart systems integration is crucial. Systems integration of adsorption chillers is challenging due to several features: (1) intrinsic dynamics; (2) close interaction between various system components; and (3) strong coupling of design, control, and operating conditions. These features lead to a variety of degrees of freedom, which make it difficult to use simple design and control rules for systems integration. To move towards optimal systems integration of adsorption chillers, this thesis provides appropriate models and methods. First of all, a model of an adsorption chiller is developed, which is accurate enough to consider quantities needed on system level, but also computationally sufficiently efficient for model-based optimizations. To demonstrate the model accuracy, the model is calibrated and validated for two types of adsorption chillers, a lab-scale one-bed adsorption chiller and a commercial two-bed adsorption chiller. Subsequently, the presented model is used for two areas of systems integration: the integration in hybrid systems and the integration within the auxiliaries. To exemplify the integration in a hybrid system, an adsorption chiller is integrated into a CO2 vapor compression cycle to efficiently provide refrigeration with natural refrigerants only. The exemplified integration identifies a significant potential for energy savings, which can be fully exploited by optimal design and control of the hybrid system. The demonstrated integration in hybrid systems is also an example for a conceptual integration, which quantifies the potential of a specific application. To integrate the adsorption chiller within the auxiliaries, an optimization-based method is presented for detailed sizing and control of all system components including auxiliaries. The presented method is demonstrated for a solar-thermally-driven adsorption chiller system and determines both, an energetically and an economically optimal design and control. In summary, the thesis provides a comprehensive framework for optimal systems integration of adsorption chillers: from model validation over conceptual integration to detailed design and control. |
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Pages: 177
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| Published: Verlag G. Mainz - July 2021 |
| Format: Paperback |
| Subjects: |
| List Price: 43.99 Pounds Sterling |
| Availability: Temporarily Out of Stock, more expected soon |
| Title: 3 of: 75 |
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| Title: Active Noise and Occlusion Effect Cancellation in Headphones and Hearing Aids |
| Series: Aachener Beiträge zu digitalen Nachrichtensystemen |
| By (author): Stefan Wilhelm Liebich |
| ISBN10-13: 3958863574 : 9783958863576 |
| The perception of oneâ s own voice is distorted when telephoning with headsets, or wearing hearing aids. The reason for this is the so-called occlusion effect, which occurs when ear canals are completely or partially closed by the headset or hearing aid. The occlusion causes amplification at low frequencies, and attenuation at high frequencies of oneâ s own voice. The unnatural perception of oneâ s own voice and of noise caused by chewing and swallowing are among the most common complaints of users. Furthermore, environmental noise might impair perception. In this thesis, both the unnatural perception of oneâ s own voice and the disturbance by environmental noise are tackled by a novel signal processing approach. The proposed solution solves the problem of the occlusion effect by actively emitting a compensation signal through the integrated loudspeaker. The approach is called Occlusion Effect Cancellation (OEC) and significantly improves the perception of oneâ s own voice and of the acoustic environment. This novel approach combines methods of active noise cancellation (ANC, Noise Cancelling Headphone) with a personalized design. The bilateral headset contains two additional microphones per side, one inner and one outer, to acquire signals for the calculation of the compensation signals. A correctly balanced processing of the two microphone signals results in a "digital ear opening" and a much more natural perception of both oneâ s own voice and of the environment. The extent of the digital ear opening is controllable. The system can also be operated as a noise cancelling headphone by changing the parameters to a conventional design to create an acoustic isolation from the environment. This thesis proposes a novel robust approach based on digital filtering to solve the described problems. A combination of feedback and feedforward filter design allows for either approaching personal silence or a natural perception of oneâ s own voice and the acoustic environment. |
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Pages: 142
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| Published: Verlag G. Mainz - August 2010 |
| Format: Paperback |
| Subjects: |
| List Price: 43.99 Pounds Sterling |
| Availability: Temporarily Out of Stock, more expected soon |
| Title: 4 of: 75 |
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| Title: Adaption of new strategies for parameterization of a microstructure-based flow stress model |
| Series: Umformtechnische Schriften |
| By (author): Wei Xiong |
| ISBN10-13: 3958861539 : 9783958861534 |
| One of the most important tools in the metal forming technology is the integrated process and microstructual simulation using Finite Element Methods (FEM). It has become more and more popular in recent years, especially in the segment of hot metal forming, e.g. open die forging of large scaled and hardly deformable materials, such as nickel-based super alloys for turbine shaft. Theoretically using this method it is possible to calculate the microstructual evolution along the whole process chain in the numerical simulation of the considered metal forming process. Based on this knowledge a series of benefits can be achieved for the practice, such as to optimize a present metal forming process, to predict the mechanical properties of the final products under the given forming conditions, to detect the possible product failures prematurely, to assist the design of a new production chain and so on. In the face of these trends of the scientific research as well as the industrial demands, different material models have been released in the market to combine the commercial FEM programs specialized in the numerical simulation of metal forming. Among others microstructure-based ow stress models show outstanding performance. Through this kind of material model not only the microstructure such as recrystallization and grain size, but also the interaction between the microstructual evolution and the working hardening, effectively ow stress, can be quantitatively represented. Towards accurate and efficient material modeling, the model parameters have to be determined conveniently and reliably. For this propose a new Hybrid strategy combining the advantages both of direct and indirect methods has been proposed using the example of StrucSim, which is a very good representative of a mircostructure-based ow stress model. At first different aspects, which lead to the disadvantages of the conventional method, i.e. direct method, were discussed. In doing so a high manganese steel was characterized as an example by stepwise graphical and regression analysis. It was found that, the precondition of direct methods, namely recording ow curves under constant Zener-hollomon-parameter conditions, are basically not possible due to both limitations of test equipment and unconquerable physical mechanism like dissipation heating. The common solution to compensate these factors may lead to further inaccuracies, uncertainties and complexities despite large testing and evaluating efforts. Further in order to improve the model quality calibrated by the conventional direct method an efficient hybrid strategy has been derived by combining inverse analysis with offline calculation of ow stress and microstructure. Three different variations of the hybrid strategy were introduced to deal with different available experimental databases, such as isothermal and non-isothermal ow curves. To demonstrate the developed routines of these three hybrid possibilities two kinds of materials including a nickel-based super alloy and a high manganese steel have been taken into account. The investigation has shown that through the introduced hybrid methods better model quality can be achieved even with less experimental data. Owing to the convenience of the inverse technique much experimental and evaluating effort and complexities can be avoided. Finally, another inverse analysis based on inhomogeneous deformation has been proposed, in which hot compression tests with double cone specimen were employed. Thanks to the inhomogeneity of strain and microstructure distribution within the specimen, it becomes possible to get sufficient relevant information as constraints for the inverse parameterization through even fewer experiments. In addition, the established routine of a hybrid strategy as well as the inverse analysis based on non-uniform deformation enhances the transferability of determined model coefficients between two materials within the same group or among similar materials. |
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Pages: 150
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| Published: Verlag G. Mainz - February 2017 |
| Format: Paperback |
| Subjects: |
| List Price: 43.99 Pounds Sterling |
| Availability: In Stock
Qty Available: 3 |
| Title: 5 of: 75 |
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| Title: Advances in biomedical NMR with spatial resolution |
| By (author): Jennifer Flohr |
| ISBN10-13: 3958862861 : 9783958862869 |
| In modern medicine, magnetic resonance imaging (MRI) is an essential diagnostic tool, which enables physicians to detect a great variety of diseases and physical injuries. The scope of possibilities encompasses neuro-, cardiovascular-, musculoskeletal-, hepatobiliary- and gastrointestinal imaging as well a magnetic resonance angiography. Besides commercially available MRI scanners, low magnetic field devices gain more and more attention because they are more compact, mostly portable, easier to handle due to the lack of cryogenic coolants, and usually come with a large cost saving. In this thesis, high magnetic field devices and unilateral NMR sensors are deployed to explore different biomedical topics. Imaging techniques are used to study the flow inside aneurysmsâ enlargements of blood vessels in the human body, whose rupture can lead to severe health issues. In an experimental flow set-up, different fluids and flow velocities are tested inside silicon aneurysm models with and without stents. These narrow tubes, which commonly consist of a metallic network, are inserted into a vessel to cut the aneurysm from the blood stream. TheNMR-MOUSER (MObileUniversal Surface Explorer), a sensor design first conceived in the mid 90s by BlÃ"mich and BlÃ"mler, and its derivative â the Fourier NMR-MOUSE â are utilized to study human and porcine skin. Outer skin layers are investigated in terms of diffusion and relaxation time profiling in laboratory and clinical studies. They assess the structural composition and susceptibility to different substances, and identify carcinogenic processes and the effect of aging and renal insufficiency. |
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Pages: 158
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| Published: Verlag G. Mainz - May 2019 |
| Format: Paperback |
| Subjects: |
| List Price: 43.99 Pounds Sterling |
| Availability: Temporarily Out of Stock, more expected soon |
| Title: 6 of: 75 |
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| Title: Advances in low-field NMR relaxometry |
| By (author): Denis Jaschtschuk |
| ISBN10-13: 3958863175 : 9783958863170 |
| In the context of this work, three unilateral NMR sensors were designed, constructed and characterized. For the new sensors, the concept was chosen to vary the angle of the polarization of the magnets. This affects the size and the position of the sensitive slice. The MOUSEPAD, based on the modified design of the Profile NMR-MOUSE with 5 mm penetration depth, achieved a penetration depth of 17 mm. The Mini-MOUSEPAD is based on the Mini-MOUSE and has an increased penetration depth of 2.5 mm. The penetration depth is a crucial parameter for investigations with unilateral NMR, since the object of interest can be arbitrary shaped and the relevant areas at higher depths might be difficult to access. Therefore, these sensors might show a strategy for further miniaturization of state-of-the-art unilateral NMR sensors. The special magnet arrangement of both sensors results in a reduction of the magnetic field strenght (4.9MHz for the MOUSEPAD and 9.0 MHz for the Mini-MOUSEPAD) and much lower gradient strenght compared to prior state of the art sensors. Consequently, the weaker diffusive attenuation leads to a decreased diffusion weighting. Furthermore, in combination with the extended lateral size of the sensitive area, it leads to an increased SNR, compared to the PM5 and Mini-MOUSE. Sensors with higher sensitivity benefit from shorter measurement times and a higher information density. The third sensor is the Hexarray. It is a compact (110 x 95 x 30 mm³, 1.6 kg) unilateral sensor with two sensitive clices. It operates at 4.9 MHz at 4 mm above the sensor surface. If one coil is oerated while the other is in the waiting period and vice versa it is possible to perform measurements quasi-simultaneously without any mutual interactions. The setup can be used to reduce the measurements time. If both spots measure a similar sample, this setup can be used to increase the SNR by adding up both decays. To exploit the full potential of these sensors, further work is necessary. |
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Pages: 120
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| Published: Verlag G. Mainz - December 2019 |
| Format: Paperback |
| Subjects: |
| List Price: 43.99 Pounds Sterling |
| Availability: Temporarily Out of Stock, more expected soon |
| Title: 7 of: 75 |
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| Title: Advances in NMR spectoscopy and imaging |
| Sub-title: Low-power rf-excitation and MRI of soils |
| By (author): Alexander Görges |
| ISBN10-13: 3958864147 : 9783958864146 |
| Nuclear Magnetic Resonance (NMR) techniques have proliferated in many fields of science and technology like bio-sensing, chemical reaction monitoring and material characterization. Since the inception of NMR as an analytical tool, improving the sensitivity by increasing the field strength has been the primary development goal. However, in order to reduce cost and environmental impact, the trend to miniaturized NMR devices and its diverse application fields enjoys increasing interest. The first part of this thesis introduces novel insights into low-power rf-excitation, which is one crucial aspect for enabling further development in this direction, by employing Frank sequences. Based on experimental data, a detailed evidence of the power savings by excitation in the linear regime is given aiming at future elimination of the rf-amplifier from the NMR spectrometer so as to allow further mobility improvements. Selective excitation by colored Frank-sequence is reported, which bears promise for solvent signal suppression and motion tagging in magnetic resonance imaging (MRI). To this end, spectroscopic quality as well as image resolution with Frank excitation was significantly improved. The aim of the second part is to provide quantitative 3D moisture content patterns of natural soil samples on the microscale, which are essential for improving geological simulations on the field scale. In the course of this, the standardized imaging sequences â zero echo timeâ (ZTE) and â ultra-short echo timeâ (UTE) were employed but also Frank-sequence excitation was implemented, reflecting its first genuine application. In order to characterize water-retention behavior of the soil samples, ZTE experiments were combined with standardized geological methods like Multi-Step Outflow (MSO) and tensiometric measurements. Compared to the established way of acquiring water-retention data, the introduced method provides a fast and precise method with low effort. |
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Pages: 149
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| Published: Verlag G. Mainz - August 2021 |
| Format: Paperback |
| Subjects: |
| List Price: 43.99 Pounds Sterling |
| Availability: Temporarily Out of Stock, more expected soon |
| Title: 8 of: 75 |
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| Title: Analysis of CSMA Based Broadcast Communication in Vehicular Networks with Hidden Stations |
| Series: Aachener Beiträge zur Mobil- und Telekommunikation |
| By (author): Yunpeng Zang |
| ISBN10-13: 3958860559 : 9783958860551 |
| This thesis studies the congestion problem at the Medium Access Control (MAC) layer of the IEEE 802.11p system in highway scenarios using an analytical approach. Using the Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA) protocol, the IEEE 802.11p system suffers from the hidden station problem. This thesis provides formal definitions for the hidden station condition and the hidden station problem and develops an analytical methodology for CSMA protocols to investigate the interaction between stations in mutual channel sensing range and hidden to each other. Analytical models are developed for broadcast communication using the generic CSMA protocol and the IEEE 802.11p MAC protocol with a one-dimensional (1-D) homogeneous network topology. Simulation studies prove the accuracy of the models in analyzing the reliability performance and the efficiency performance of CSMA broadcast communication with hidden stations. The performance of Cooperative Awareness Message (CAM) in IEEE 802.11p network is analyzed for highway scenarios using the developed analytical models. The study reveals that in a hidden station scenario the reliability performance of the CAM broadcast communication deteriorates with increased topological distance between the transmitter and the receiver. This study provides quantitative analysis of this performance with respect to network density, frame length, traffic load and settings of the IEEE 802.11p MAC protocol. Analysis of the mean update interval of CAM at a receiver vehicle discovers though in general the performance degrades with increased network density, the update interval of CAM frames from a particular vehicle in the vicinity of the receiver, e.g. with a topological distance less than 8 between the transmitter and the receiver, can be easily maintained below 1 second by using control mechanisms like transmit power control, transmit rate control and link control. The analytical models developed in this work provide quantitative guidance on optimizing protocol parameters and utilization of these control mechanisms. |
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Pages: 170
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| Published: Verlag G. Mainz - October 2015 |
| Format: Paperback |
| Subjects: |
| List Price: 43.99 Pounds Sterling |
| Availability: In Stock
Qty Available: 1 |
| Title: 9 of: 75 |
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| Title: Application of Manganese Pincer Complexes for Hydrogenation and Dehydrogenation Reactions |
| By (author): Viktoriia Zubar |
| ISBN10-13: 3958863744 : 9783958863743 |
| On the way towards sustainable and green chemistry, scientists found a key technology which allows chemical transformations to proceed with minimum waste generation and energy consumption. The key is transition metal catalysis which is also attractive from an economical point of view. At the end of 19th century, Alfred Werner defined basics of coordination chemistry which were significant for the development of transition metal catalysis. In the 1930s, the Oxo Process, in which olefins react with syngas to produce linear and branched aldehydes, was developed by Otto Roelen. The reaction is still widely used and allows to produce millions metric tons of oxo chemicals. A following milestone in transition metal catalysis occurred in the 1950s when the Wacker Process was developed. The reaction allows to oxidize olefins to aldehydes and ketones with the use of PdCl2 as catalyst. Many other reactions were developed involving transition metal catalysis, including important processes such as C-C bond formations, site selective C-H bond activation, arylation of amines and alcohols and others which have been also applied in industrial processes to obtain bulk chemicals, fine chemicals and polymers. Another indicator highlighting the importance of homogeneous transition metal catalysis is the acknowledgement by the Noble Prize committee. Thus, in 2001, the Nobel Prize in chemistry was awarded jointly to William S. Knowles, Ryoji Noyori and K. Barry Sharpless for their work on transition metal catalysed asymmetric hydrogenation and oxidation reactions. Later in 2005, Yves 0Chauvin, Robert H. Grubbs and Richard R. Schrock were selected for the Noble Prize in chemistry for their work on the development of the metathesis reaction in organic synthesis. And finally, recent Noble Prize in chemistry in 2010 was awarded to Richard F. Heck, Ei-ichi Negishi and Akira Suzuki for palladium-catalysed cross coupling reactions in organic synthesis. Until recently, reports featuring homogeneous transition metal catalysis were focused on using rare and expensive metals. The application of noble metals raises major concern, as they are toxic and consequently they produce toxic waste. And to their low availability (listed as critical raw materials for European Union), noble metals require difficult extraction from the Earthâ s crust. |
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Pages: 142
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| Published: Verlag G. Mainz - October 2020 |
| Format: Paperback |
| Subjects: |
| List Price: 43.99 Pounds Sterling |
| Availability: In Stock
Qty Available: 1 |
| Title: 10 of: 75 |
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