bluuebunny/crossref_metadata_2025_split huggingface dataset:
Studien zum Ablauf der Substitution, XXII. Über den polaren und radikalischen Reaktionsverlauf der Umsetzung von Diacetylperoxyd mit (prim., sek. und tert.) Aminen, Phosphinen, Arsinen, Thioäthern und Äthern
Authors: Horner Leopold , Anders Bertram 
Published: May 2007

AbstractDas Ausmaß des Spontanzerfalls des Acetoxylradikals in CO2 und Methylradikal erlaubt die Entscheidung, ob und in welchem Maße Amine, Phosphine, Thioäther und Äther die OO‐Brücke des Diacetylperoxyds im Sinne einer Redoxreaktion (A) oder nucleophil (B) öffnen (Diacetylperoxyd‐CO2‐Methode). Primäre aromatische Amine, tertiäre Phosphine und Arsine sowie Thioäther reagieren polar (nach B, ohne CO2‐Entwicklung), sekundäre und tertiäre Amine in Abhängigkeit von der Struktur der Amine und der Diacylperoxyde sowohl nach A als auch nach B. Diacetylperoxyd zersetzt sich in Äther und Tribenzylamin ausschließlich unter Bildung von CO2 und α‐acetoxylierten Äthern bzw. Aminen.
Mitbearbeitet von Horst Müller Metallhydrazide, III. Aminierung von Acridin und Phenanthridin mit Natriumhydrazid bzw. Natrium‐N.N‐dimethyl‐hydrazid
Authors: Kauffmann Thomas , Hacker Herbert 
Published: May 2007

AbstractIm Gegensatz zu den entsprechenden Addukten des Pyridins oder Isochinolins, die unter den gleichen Bedingungen Wasserstoff eliminieren, stabilisieren sich die aus Natriumhydrazid oder Natrium‐N.N‐dimethyl‐hydrazid und Acridin bzw. Phenanthridin gebildeten Addukte beim Erwärmen auf 50–60° durch Abspaltung von Ammoniak bzw. Dimethylamin unter Bildung des Natrium‐salzes des 9‐Amino‐acridins bzw. 9‐Amino‐phenanthridins. – Bei der Hydrolyse des Adduktes aus Acridin und Natrium‐N.N‐dimethyl‐hydrazid erhält man das noch nicht beschriebene, überraschend stabile 9‐[N.N‐Dimethyl‐hydrazino]‐9.10‐dihydro‐acridin.
Über die Wolff‐Kishner‐Reduktion ω‐ungesättigter Oxocarbonsäuren
Authors: Hünig Siegfried , Eckardt Wolfgang 
Published: May 2007

AbstractDie Wolff‐Kishner‐Reduktion ω‐ungesättigter Oxocarbonsäuren führt teilweise zur Wanderung wie zur Hydrierung der endständigen Doppelbindung. Diese Nebenreaktionen werden and der Δ10‐Undecensäure studiert und an der 7‐Oxononansäure möglichst milde Reduktionsbedingungen ermittelt. Die Analysenmethoden werden ausführlich beschrieben.
Carbonsäurederivate, V. Substituierte Dithiocarbonsäuren und Ketenmercaptale
Authors: Gompper Rudolf , Töpfl Werner 
Published: May 2007

AbstractDie Herstellung von Dithiocarbonsäuren aus CH‐aciden Verbindungen und Schwefelkohlenstoff wird beschrieben. Die Alkylierung ihrer Salze führt zu substituierten Ketenmercaptalen; bei der Oxydation entstehen Trithiacyclopentane und Dithiacyclobutane (Desaurine), letzter auch bei der Acylierung. Die Umsetzung mit Äthylenimin liefert Thiazolidine. Die Struktur (Tautomerie) der Dithiocarbonsäureester und Ketenmercaptale wird an Hand der IR‐Spektren diskutiert.
Versuche mit Raney‐Nickel
Authors: Schönberg Alexander , Borsowski Karl‐Heinz , Singer Erich 
Published: May 2007

AbstractEine Reihe von Polyaryl‐äthan‐, ‐äthylen‐ und ‐propan‐Derivaten liefert bei der Behandlung mit aktivem Raney‐Nickel in siedendem Xylol unter Sprengung von CC‐Bindungen Diarylmethane. Bei der Einwirkung von Raney‐Nickel auf Organo‐Phosphor‐ (bzw. ‐Arsen‐, ‐Antimon‐ und ‐Quecksilber‐) Verbindungen wurde neben Hydrogenolyse der CP(As; Sb; Hg)‐Bindungen auch die Verknüpfung der aromatischen Reste beobachtet, die z. B. die Bildung von Binaphthyl‐(1.1′) aus Tri‐naphthyl‐(1)‐arsin. Beispiele für die Hydrogenolyse von CN‐Bindungen und für den Ersatz von Brom in aromatischer Bindung durch Wasserstoff werden gegeben.
Über 3‐Hydroxy‐fluoranthen‐carbonsäuren‐(1), ‐(2) und ‐(10)
Authors: Sieglitz Adolf , Tröster Helmut , Böhme Peter 
Published: May 2007

AbstractDurch Behandlung mit Luft in alkalischem Milieu werden Carbonsäurederivate des 3‐Oxo‐1.2.3.lob‐tetrahydro‐fluoranthens in entsprechende 3‐Hydroxy‐fluoranthencarbonsäuren und ihre Abkömmlinge übergeführt. Durch Belichtung von 3‐Hydroxy‐fluoranthen entsteht 1‐Carboxy‐fluoren‐essigsäure‐(9). Entsprechend wird aus 3‐Hydroxy‐fluoranthen‐carbonsäure‐(1) 1‐Carboxy‐fluoren‐malonsäure‐(9) gebildet.
Oligosaccharidsynthesen, III. Synthesen α‐ und β‐konfigurierter Disaccharide
Authors: Bredereck Hellmut , Wagner Adolf , Geissel Dieter , Gross Peter , Hutten Ulrich , Ott Hermann 
Published: May 2007

AbstractDie Umsetzungen von Tritylzuckern mit Acylhalogenglucosen und ‐galaktosen in Gegenwart von Silberperchlorat führen zu β‐verknüpften, mit α‐Aceto‐chlor‐mannose zu α‐verknüpften Disacchariden.
Nucleophile Carben‐Chemie, IV. Reaktion des Bis‐[1.3‐diphenyl‐imidazolidinylidens‐(2)] mit einigen Carbonylverbindungen
Authors: Wanzlick Hans‐Werner , Kleiner Hanss‐Jerg 
Published: May 2007

AbstractDie Reaktivität des Bis‐[1.3‐diphenyl‐ imidazolidinylidens‐(2)] gegenüber Furfurol, aromatischen Ketonen und einem α,β‐ungesättigten Keton wird untersucht.
Über kationische Kohlenoxidkomplexe, II. Bildungsweisen homogener und phosphinsubstituierter kationischer Kohlenoxidkomplexe von Mangan(I) und Rhenium(I)
Authors: Kruck Thomas , Noack Manfred 
Published: May 2007

AbstractMit Halogenacceptoren wie AlCl3, FeCl3 und ZnCl2 bilden Mn(CO)5Cl, Re(CO)5Cl sowie phosphinsubstituierte Mangancarbonylchloride unter CO‐Druck bei erhöhter Temperatur in einer Trockenreaktion kationische Kohlenoxidkomplexe gemäß

ZnCl2 reagiert hierbei merklich schwerer und nur bei großem überschuß; es entstehen im allgemeinen Hexachlorodizinkate entsprechend

Die salzartige Struktur der Verbindungen wird durch Messung der elektrolytischen Leitfähigkeit und magnetischen Suszeptibilität sowie durch Fällungsreaktionen mit komplexen Anionen nachgewiesen. An Hand der IR‐Spektren wird auf trans‐ Stellung der beiden Phosphinliganden im oktaedrischen Komplex {Mn(CO)4[P(C6H5)3]2}⊕ geschlossen.
Über kationische Kohlenoxidkomplexe, III. Heterogene kationische Kohlenoxidkomplexe von Mangan(I) und Rhenium(I)
Authors: Kruck Thomas , Höfler Mathias 
Published: May 2007

AbstractSubstituierte Mangan‐ und Rheniumcarbonylchloride bilden mit AlCl3, FeCl3 und ZnCl2 unter CO‐Druck heterogene, kationische Kohlenoxidkomplexe von Mangan(I) und Rhenium(I). – Für die Darstellung der Kationen [Mn(CO)4L2] ⊕ (L = P(6H5)3, P(OC 6H5)3, Te(C6H5)2) erwies sich die drucklose Umsetzung von CO mit der Benzolsuspension von AlCl3 und Mangancarbonylchlorid als besonders günstig. Die ionogene Struktur der neuartigen Carbonylkationen wird durch Fällung mit geeigneten Anionen sowie durch Messung der Leitfähigkeit und der magnetischen Suszeptibilität bewiesen.
Über die Sulfochlorierung aliphatischer Amine
Authors: Feichtinger Hans 
Published: May 2007

AbstractDurch Sulfochlorierung lassen sich aus den Hydrochloriden des n‐Propyl‐, Isobutyl‐ und n‐Butylamins präparative Mengen einheitlicher Aminoalkan‐sulfo‐chlorid‐hydrochloride gewinnen. Die Konstitution der Hydrochloride wird durch Cyclodehydrochlorierung zu Sultamen und anschließende Hydrochlorolyse unter Ringöffnung bewiesen.
Security and performance enhancements to OGSA‐DAI for Grid data virtualization
Authors: Adamski Marcin , Kulczewski Michal , Kurowski Krzysztof , Nabrzyski Jarek , Hume Alastair 
Published: May 2007

AbstractIn this paper we describe our work on enabling dynamic access control and secure management over federated data resources, such as relational or XML databases exposed to public network infrastructures via OGSA‐DAI middleware. We have proposed some extensions to the OGSA‐DAI architecture and successfully implemented new mechanisms enabling secure communication and distributed data integrity along with fine‐grain authorization and policy enforcement to minimize the complexity of the security right management. As a proof of concept some preliminary results of various performance tests of our solutions are also presented in this paper. We then analyze our achievements and describe future work and research. Copyright © 2007 John Wiley & Sons, Ltd.
Performance prediction for a code with data‐dependent runtimes
Authors: Jarvis S. A. , Foley B. P. , Isitt P. J. , Spooner D. P. , Rueckert D. , Nudd G. R. 
Published: May 2007

AbstractIn this paper we present a predictive performance model for a key biomedical imaging application found as part of the U.K. e‐Science Information eXtraction from Images (IXI) project. This code represents a significant challenge for our existing performance prediction tools as it has internal structures that exhibit highly variable runtimes depending on qualities in the input data provided. Since the runtime can vary by more than an order of magnitude, it has been difficult to apply meaningful quality of service criteria to workflows that use this code. The model developed here is used in the context of an interactive scheduling system which provides rapid feedback to the users, allowing them to tailor their workloads to available resources or to allocate extra resources to scheduled workloads. Copyright © 2007 John Wiley & Sons, Ltd.
Transcriptome changes associated with instructed learning in the barn owl auditory localization pathway
Authors: Swofford Janet A. , DeBello William M. 
Published: May 2007

AbstractOwls reared wearing prismatic spectacles learn to make adaptive orienting movements. This instructed learning depends on re‐calibration of the midbrain auditory space map, which in turn involves the formation of new synapses. Here we investigated whether these processes are associated with differential gene expression, using longSAGE. Newly fledged owls were reared for 8–36 days with prism or control lenses at which time the extent of learning was quantified by electrophysiological mapping. Transciptome profiles were obtained from the inferior colliculus (IC), the major site of synaptic plasticity, and the optic tectum (OT), which provides an instructive signal that controls the direction and extent of plasticity. Twenty‐two differentially expressed sequence tags were identified in IC and 36 in OT, out of more than 35,000 unique tags. Of these, only four were regulated in both structures. These results indicate that regulation of two largely independent gene clusters is associated with synaptic remodeling (in IC) and generation of the instructive signal (in OT). Real‐time PCR data confirmed the changes for two transcripts, ubiquitin/polyubiquitin and tyrosine 3‐monooxgenase/tryotophan 5‐monooxygenase activation protein, theta subunit (YWHAQ; also referred to as 14‐3‐3 protein). Ubiquitin was downregulated in IC, consistent with a model in which protein degradation pathways act as an inhibitory constraint on synaptogenesis. YWHAQ was up‐regulated in OT, indicating a role in the synthesis or delivery of instructive information. In total, our results provide a path towards unraveling molecular cascades that link naturalistic experience with synaptic remodeling and, ultimately, with the expression of learned behavior. © 2007 Wiley Periodicals, Inc. Develop Neurobiol, 2007.
The Influence of Steric Pressure on the Structure of Homodimetallic Rhodium(I) and Iridium(I) Complexes Containing a Bis(bidentate) Phosphane Ligand
Authors: Bachmann Christian , Gutmann Rene , Czermak Georg , Dumfort Alexander , Eller Sylvia , Fessler Markus , Kopacka Holger , Ongania Karl‐Hans , Brüggeller Peter 
Published: May 2007

AbstractFifteen novel homodimetallic RhI and IrI complexes containing the bis(bidentate) phosphane ligand cis,trans,cis‐1,2,3,4‐tetrakis(diphenylphosphanyl)cyclobutane (dppcb) were prepared and characterized by NMR spectroscopy (1H, 13C{1H}, 31P{1H}), mass spectrometry, IR spectroscopy, elemental analyses and melting points. Furthermore, the solid‐state structures of seven of these new compounds were fully determined by single‐crystal X‐ray diffraction analyses to study the influence of steric pressure. The precursor complex [Rh2(η4‐cod)2(dppcb)]X2 (1), X– = BF4–, PF6–, SbF6–, completely characterized by its X‐ray structure, smoothly reacts with mono‐ or bidentate ligands containing phosphorus or nitrogen donor atoms. Thus, monophosphanes and monophosphites produce compounds of the structure type [Rh2L4(dppcb)](SbF6)2 [L = PMe2Ph, 2; PMePh2, 3; P(OMe)3, 5; P(OPh)3, 6]. The X‐ray structures of 3 and 6 show that PMePh2 and P(OPh)3 are capable of compensating steric interactions. The treatment of 1 with diphosphanes leads to the structure type [Rh2L2(dppcb)](SbF6)2 [L = bis(diphosphanyl)methane, dppm, 7; bis(diphenylphosphanyl)amine, dppam, 8; 1,2‐bis(diphenylphosphanyl)ethane, dppe, 9; cis‐1,2‐bis(diphenylphosphanyl)ethene, cis‐dppen, 10]. The X‐ray structures of 8, 9 and 10 clearly indicate the onset of steric pressure as a consequence of mechanical coupling, which results in two different coordination moieties for homodimetallic species 9 and 10. Under steric pressure, the quadrant effects of dppcb and dppe become comparable to RhI complexes. The use of mono‐ or bidentate ligands containing nitrogen donor atoms leads to the compounds [Rh2(pyridine)4(dppcb)](SbF6)2 (11), [Rh2(2,2′‐bipyridine)2(dppcb)](SbF6)2 (12) and [Rh2(1,10‐phenanthroline)2(dppcb)](SbF6)2 (13). The crystal structures of 1 and the novel complex [Ir2(η4‐cod)2(dppcb)]X2 (14), X– = BF4–, SbF6–, are isomorphous. However, it was only possible to produce restricted examples of derivatives of 14 owing to the reluctance of 14 to release cod. Thus, monophosphanes lead to the five‐coordinate species [Ir2(η4‐cod)2(PMe2Ph)2(dppcb)](BF4)2 (15), whereas the four‐coordinate compound [Ir2(PMePh2)4(dppcb)](BF4)2 (16) is formed by using the sterically more demanding ligand PMePh2 instead of PMe2Ph. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
Stereoselective Reactions of (E,E)‐2,3,6,7‐Tetramethyl‐1,8‐Bis(trimethylsilyl)octa‐2,6‐diene with Aldehydes and Acyl Chlorides
Authors: Aouf Chahinez , El Abed Douniazad , Ibrahim‐Ouali Malika , Giorgi Michel , Santelli Maurice 
Published: May 2007

AbstractThe titanium tetrachloride mediated addition reaction of (E,E)‐2,3,6,7‐tetramethyl‐1,8‐bis(trimethylsilyl)octa‐2,6‐diene to aldehydes and acyl chlorides is described. Aldehydes undergo simple allylation except p‐anisaldehyde, which leads to cyclopentane resulting from double allylation. From acyl chlorides, highly substituted meso cyclopentanols bearing 1,3‐diquaternary carbon atoms separated by a tertiarycarbinol are obtained. The structures of two cyclopentanols are confirmed by X‐ray analysis. From the structure of the cyclopentanols, a reaction mechanism for the double allylation of the acyl chloride by diallylsilane could be proposed. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
Synthesis of Enantiomerically Pure cis‐ and trans‐4‐Amino‐1‐oxyl‐2,2,6,6‐tetramethylpiperidine‐3‐carboxylic Acid: A Spin‐Labelled, Cyclic, Chiral β‐Amino Acid, and 3D‐Structural Analysis of a Doubly Spin‐Labelled β‐Hexapeptide
Authors: Wright Karen , Sarciaux Matthieu , de Castries Augustin , Wakselman Michel , Mazaleyrat Jean‐Paul , Toffoletti Antonio , Corvaja Carlo , Crisma Marco , Peggion Cristina , Formaggio Fernando , Toniolo Claudio 
Published: May 2007

AbstractAmination of 3‐carboxymethyl‐1‐oxyl‐2,2,6,6‐tetramethyl‐4‐piperidone (1) with either (R)‐ or (S)‐α‐methylbenzylamine gave corresponding enamines 2. Whereas the reduction with NaBH3CN/CH3COOH afforded predominantly a mixture of two possible cis diastereomers of 3, (1′R,3S,4S)/(1′R,3R,4R) or (1′S,3R,4R)/(1′S,3S,4S), which could be separated by crystallisation of their HCl salts, the use of NaBH4/(CH3)2CHCOOH as the reducing agent resulted in a mixture of one trans‐ and one cis diastereomer of 3 (1′R,3S,4R)/(1′R,3R,4R) or (1′S,3R,4S)/(1′S,3S,4S) in varying proportions depending upon the conditions used. The stereochemistry of the four diastereomers of 3 was clearly established by X‐ray diffraction analysis of one of them, combined with 1H NMR spectroscopic studies after nitroxide reduction. Removal of the chiral auxiliary from the separated diastereomers of 3 by hydrogenation and regeneration of the nitroxide radical gave expected amino esters 4. A model β‐hexapeptide containing (3R,4S)‐β‐TOAC combined with (1S,2S)‐2‐aminocyclohexane carboxylic acid was synthesised by solution methods and its preferred conformation (314‐helix) was assessed by FTIR absorption, CD, and EPR spectroscopy.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
Silver‐ and Coomassie‐staining protocols: Detection limits and compatibility with ESI MS
Authors: Winkler Christiane , Denker Katrin , Wortelkamp Stefanie , Sickmann Albert 
Published: May 2007

AbstractStaining protocols for PAGE have to be sensitive and should not impair further MS analysis of selected samples. In this study, the MS compatibility of different silver‐ and Coomassie‐staining protocols with a nano‐LC‐MS/MS system was systematically elucidated. Altogether, 13 different silver‐staining, 1 imidazole‐staining and 2 Coomassie‐staining protocols were used and compared to each other for their achieved sequence coverage and their detection sensitivity. Three proteins were used as model proteins (bovine serum albumin, rabbit L‐lactate dehydrogenase, bovine milk β‐lactoglobulin) in decreasing concentration (12 pmol down to 30 fmol) and different staining protocols were applied. The conclusion of this study is that two silver‐staining protocols (Blum, H. et al.,. Electrophoresis 1987, 8, 93–99 and Shevchenko, A. et al.,. Anal. Chem. 1996, 68, 850–858) combine good sequence coverage and good sensitivity and are recommended for nano‐LC‐MS/MS analysis.
Rimonabant reduces obesity-associated hepatic steatosis and features of metabolic syndrome in obese Zucker fa/fa rats
Authors: Gary-Bobo Magali , Elachouri Ghizlane , Gallas Jean François , Janiak Philip , Marini Pietro , Ravinet-Trillou Christine , Chabbert Michèle , Cruccioli Noël , Pfersdorff Christian , Roque Claude , Arnone Michèle , Croci Tiziano , Soubrié Philippe , Oury-Donat Florence , Maffrand Jean Pierre , Scatton Bernard , Lacheretz Frederic , Le Fur Gérard , Herbert Jean Marc , Bensaid Mohammed 
Published: May 2007

Abstract

This study investigated the effects of rimonabant (SR141716), an antagonist of the cannabinoid receptor type 1 (CB1), on obesity-associated hepatic steatosis and related features of metabolic syndrome: inflammation (elevated plasma levels of tumor necrosis factor alpha [TNFα]), dyslipidemia, and reduced plasma levels of adiponectin. We report that oral treatment of obese (fa/fa) rats with rimonabant (30 mg/kg) daily for 8 weeks abolished hepatic steatosis. This treatment reduced hepatomegaly, reduced elevation of plasma levels of enzyme markers of hepatic damage (alanine aminotransferase, gamma glutamyltransferase, and alkaline phosphatase) and decreased the high level of local hepatic TNFα currently associated with steatohepatitis. In parallel, treatment of obese (fa/fa) rats with rimonabant reduced the high plasma level of the proinflammatory cytokine TNFα and increased the reduced plasma level of the anti-inflammatory hormone adiponectin. Finally, rimonabant treatment also improved dyslipidemia by both decreasing plasma levels of triglycerides, free fatty acids, and total cholesterol and increasing the HDLc/LDLc ratio. All the effects of rimonabant found in this study were not or only slightly observed in pair-fed obese animals, highlighting the additional beneficial effects of treatment with rimonabant compared to diet. These results demonstrate that rimonabant plays a hepatoprotective role and suggest that this CB1 receptor antagonist potentially has clinical applications in the treatment of obesity-associated liver diseases and related features of metabolic syndrome. (HEPATOLOGY 2007.)
Expatriates in their own home: A new twist in the human resource management strategies of japanese mncs
Authors: Bird Allan , Mukuda May 
Published: May 2007

AbstractLiaison positions in an overseas subsidiary represent a vital link to the parent company. Staffing this position constitutes a critical HRM decision. Based on exploratory interviews conducted with personnel managers and foreign employees, we examine an emerging approach to meeting this staffing need which entails hiring non‐Japanese as employees of the parent company, retaining them at headquarters in Japan for three to four years, then assigning them back to their own countries as expatriates. We discuss this approach's underlying rationale, its advantages and disadvantages, and its potential implications for future IHRM developments within Japanese MNCs.
TSE with average‐specific phase encoding ordering for motion detection and artifact suppression
Authors: Zhang Ling , Kholmovski Eugene G. , Guo Junyu , Parker Dennis L. 
Published: May 2007

AbstractPurposeTo detect motion‐corrupted measurements in multiaverage turbo‐spin‐echo (TSE) acquisitions and reduce motion artifacts in reconstructed images.Materials and MethodsAn average‐specific phase encoding (PE) ordering scheme was developed for multiaverage TSE sequences in which each echo train is assigned a unique PE pattern for each preaveraged image (PAI). A motion detection algorithm is developed based on this new PE ordering to identify which echo trains in which PAIs are motion‐corrupted. The detected PE views are discarded and replaced by uncorrupted k‐space data of the nearest PAI. Both phantom and human studies were performed to investigate the effectiveness of motion artifact reduction using the proposed method.ResultsMotion‐corrupted echo trains were successfully detected in all phantom and human experiments. Significant motion artifact suppression has been achieved for most studies. The residual artifacts in the reconstructed images are mainly caused by residual inconsistencies that remain after the corrupted k‐space data is corrected.ConclusionThe proposed method combines a novel data acquisition scheme, a robust motion detection algorithm, and a simple motion correction algorithm. It is effective in reducing motion artifacts for images corrupted by either bulk motion or local motion that occasionally happens during data acquisition. J. Magn. Reson. Imaging 2007;25:1271–1282. © 2007 Wiley‐Liss, Inc.
Insight into RF power requirements and B1 field homogeneity for human MRI via rigorous FDTD approach
Authors: Ibrahim Tamer S. , Tang Lin 
Published: May 2007

AbstractPurposeTo study the dependence of radiofrequency (RF) power deposition on B0 field strength for different loads and excitation mechanisms.Material and MethodsStudies were performed utilizing a finite difference time domain (FDTD) model that treats the transmit array and the load as a single system. Since it was possible to achieve homogenous excitations across the human head model by varying the amplitudes/phases of the voltages driving the transmit array, studies of the RF power/B0 field strength (frequency) dependence were achievable under well‐defined/fixed/homogenous RF excitation.ResultsAnalysis illustrating the regime in which the RF power is dependent on the square of the operating frequency is presented. Detailed studies focusing on the RF power requirements as a function of number of excitation ports, driving mechanism, and orientations/positioning within the load are presented.ConclusionWith variable phase/amplitude excitation, as a function of frequency, the peak‐then‐decrease relation observed in the upper axial slices of brain with quadrature excitation becomes more evident in the lower slices as well. Additionally, homogeneity optimization targeted at minimizing the ratio of maximum/minimum B1+ field intensity within the region of interest, typically results in increased RF power requirements (standard deviation was not considered in this study). Increasing the number of excitation ports, however, can result in significant RF power reduction. J. Magn. Reson. Imaging 2007;25:1235–1247. © 2007 Wiley‐Liss, Inc.