A dielectric is an electrical insulator that can be polarized by an applied electric field. When a dielectric material is placed in an electric field, electric charges do not flow through the material as they do in an electrical conductor but only shift from their average equilibrium positions causing dielectric polarization; because of dielectric polarization, positive charges are displaced in the direction of the field and negative charges shift in the direction opposite to the field. This creates an internal electric field. If a dielectric is composed of weakly bonded molecules, those molecules not only become polarized, but reorient so that their symmetry axes align to the field; the study of dielectric properties concerns storage and dissipation of electric and magnetic energy in materials. Dielectrics are important for explaining various phenomena in electronics, solid-state physics, cell biophysics. Although the term insulator implies low electrical conduction, dielectric means materials with a high polarizability.
The latter is expressed by a number called the relative permittivity. The term insulator is used to indicate electrical obstruction while the term dielectric is used to indicate the energy storing capacity of the material. A common example of a dielectric is the electrically insulating material between the metallic plates of a capacitor; the polarization of the dielectric by the applied electric field increases the capacitor's surface charge for the given electric field strength. The term dielectric was coined by William Whewell in response to a request from Michael Faraday. A perfect dielectric is a material with zero electrical conductivity, thus exhibiting only a displacement current; the electric susceptibility χe of a dielectric material is a measure of how it polarizes in response to an electric field. This, in turn, determines the electric permittivity of the material and thus influences many other phenomena in that medium, from the capacitance of capacitors to the speed of light, it is defined as the constant of proportionality relating an electric field E to the induced dielectric polarization density P such that P = ε 0 χ e E, where ε0 is the electric permittivity of free space.
The susceptibility of a medium is related to its relative permittivity εr by χ e = ε r − 1. So in the case of a vacuum, χ e = 0; the electric displacement D is related to the polarization density P by D = ε 0 E + P = ε 0 E = ε 0 ε r E. In general, a material cannot polarize instantaneously in response to an applied field; the more general formulation as a function of time is P = ε 0 ∫ − ∞ t χ e E d t ′. That is, the polarization is a convolution of the electric field at previous times with time-dependent susceptibility given by χe; the upper limit of this integral can be extended to infinity as well if one defines χe = 0 for Δt < 0. An instantaneous response corresponds to Dirac delta function susceptibility χe = χeδ, it is more convenient in a linear system to take the Fourier transform and write this relationship as a function of frequency. Due to the convolution theorem, the integral becomes a simple product, P = ε 0 χ e E; the susceptibility is frequency dependent. The change of susceptibility with respect to frequency characterizes the dispersion properties of the material.
Moreover, the fact that the polarization can only depend on the electric field at previous times, a consequence of causality, imposes Kramers–Kronig constraints on the real and imaginary parts of the susceptibility χe. In the classical approach to the dielectric model, a material is made up of atoms; each atom consists of a cloud of negative charge bound to and surrounding a positive point charge at its centre. In the presence of an electric field the charge cloud is distorted, as shown in the top right of the figure; this can be reduced to a simple dipole
This is a list of musicology topics. Musicology is the scholarly study of music. A person who studies music is a musicologist; the word is used in narrow and broad senses. In the narrow sense, musicology is confined to the music history of Western culture. In the intermediate sense, it includes all relevant cultures and a range of musical forms, styles and traditions, but tends to be confined to the humanities - a combination of historical musicology and the humanities of systematic musicology. In the broad sense, it includes all musically relevant disciplines and all manifestations of music in all cultures, so it includes all of systematic musicology. American Musicological Society Art music Bibliography of Music Literature Bisector Byzantine chant Campanology Catchiness Chinese musicology CHOMBEC Cognitive musicology Cognitive neuroscience of music Computational musicology Contemporary harpsichord Department of Musicology Claudio Di Veroli Diatonic set theory Dickinson classification Documentation Centre for Music Ecomusicology Embodied music cognition Ethnomusicology Evolutionary musicology Exploring Music Fanfare Forschungsinstitut für Musiktheater Gebrauchsmusik Harshness History of classical music traditions Berthold Hoeckner Institute for History of Musical Reception and Interpretation International Research Center for Traditional Polyphony Jazz collections at the University Library of Southern Denmark Liudmila Kovnatskaya Ludomusicology Melody type Mensural notation Music and politics Music history Music psychology The Music Trades Musica poetica Musical gesture New musicology Opus Organology Psychoanalysis and music Rastrum Répertoire International des Sources Musicales Royal Musical Association Russian Orthodox bell ringing Schizophonia Single affect principle Sociomusicology Sonus Sound culture Spectromorphology State Institute for Music Research Systematic musicology Tanabe Hisao Prize The Musical Leader Timbral listening Tonkunst Treatise on Instrumentation Tune-family Vijayanagara musicological nonet Virtual Library of Musicology Whimbling iron White power music Women in Music Znamenny chant
The Minimum Information for Publication of Quantitative Real-Time PCR Experiments guidelines are a set of protocols for conducting and reporting quantitative real-time PCR experiments and data, as devised by Bustin et al. in 2009. They were devised after a paper was published in 2002 that claimed to detect measles virus in children with autism through the use of RT-qPCR, but the results proved to be unreproducible by other scientists; the authors themselves did not try to reproduce them and the raw data was found to have a large amount of errors and basic mistakes in analysis. This incident prompted Stephen Bustin to create the MIQE guidelines to provide a baseline level of quality for qPCR data published in scientific literature; the MIQE guidelines were created due to the low quality of qPCR data submitted to academic journals at the time, only becoming more common as Next Generation Sequencing machinery allowed for such experiments to be run for a cheaper cost. Because the technique is utilized across all of science in multiple fields, the instruments and designs of how qPCR is used differs greatly.
To help improve overall quality, the MIQE guidelines were made as generalized suggestions on basic experimental procedures and forms of data that should be collected as a minimum level of reported information for other researchers to understand and use when reading the published material. Setting up a recognized and agreed upon set of guidelines such as these was deemed important by the scientific community due to the increasing amount of scientific work coming from developing countries with many different languages and protocols. In 2009, an international group of scientists headed by Stephen Bustin collaborated to put together a set of guidelines on how to perform qPCR and what forms of data should be collected and published in the process; this allowed editors and reviewers of scientific journals to employ the guidelines when looking over a submitted paper that included qPCR data. Thus, the guidelines were set up as a sort of checklist for each step of the procedure with certain items being marked as essential when submitting data for publication and others marked as just desirable.
An additional version of the guidelines was published in September 2010 for use with fluorescence-based quantitative real-time PCR. It acted as a précis for the broader form of the guidelines. Other researchers have been creating further versions for specific forms of qPCR that may require a supplementary or different set of items to check, including single-cell qPCR and digital PCR. Appropriate adherence to the existing MIQE guidelines has been overviewed in other scientific areas, including photobiomodulation and clinical biomarkers, it was noted by Bustin in 2014 that there was some amount of uptake and usage of the MIQE guidelines within the scientific community, but there were still far too many published papers with qPCR experiments that lacked the most basic of data presentation and proper confirmation of effectiveness for said data. These studies retained major reproducibility issues, where the conclusions of their evidence could not be replicated by other researchers, throwing the initial results into doubt.
All of this was despite many papers directly citing Bustin's original MIQE publication, but not following through on the guideline checklist of material in their own experiments. However, some researchers have pointed out at least some success, with a number of papers being rejected by academic journals for publication due to failing to pass MIQE checklists. Other studies have been retracted after the fact once their lack of proper data to pass the MIQE guidelines was noted and publicly pointed out to the journal editors; when setting up their new comparative qPCR systems titled "Dots in Boxes" in 2017, New England Biolabs stated that they had designed the data collection portion around the MIQE guidelines so that the data fit all the minimum parameter checklists in the protocols. Other scientific instrument companies have assisted in guideline compliance by purposefully tailoring their devices for them, including Bio-Rad creating an mobile app that allows for active marking of the MIQE checklist as each step is completed.
The MIQE guidelines are split up into 9 different sections. These include not only considerations for doing the qPCR itself, but how the resulting data is collected and presented. An important part of the latter is including information relating to the analysis software used and submitting the raw data to the relevant databases. Large portions of the guidelines include basic actions that would be included in experiments and publications regardless, such as an item for describing the experimental and control group differences. Other such information includes; these two pieces are defined as essential for any study. This section includes two desirable points, which are pointing out whether the author's laboratory itself or a core laboratory of the university or organization conducted the qPCR assay and an acknowledgement of any other individuals that contributed to the work; the essential requirements that samples and sample material must meet includes a description of the sample, what form of dissection was used, what processing method was done, whether the samples were frozen or fixed and how long did it take, what sample conditions were used.
It is desirable to know the volume or mass of the sample, processed for the qPCR. For the process of extracting the DNA/RNA, there are a number of essential guidelines; this includes a description of the extraction process done, a statement on what DNA extraction kit was used a