111,868 research outputs found
Nanomechanical properties of phospholipid microbubbles
No full textThis study uses atomic force microscopy (AFM) force-deformation (F-Delta) curves to investigate for the first time the Young's modulus of a phospholipid microbubble (MB) ultrasound contrast agent. The stiffness of the MBs was calculated from the gradient of the F-Delta curves, and the Young's modulus of the MB shell was calculated by employing two different mechanical models based on the Reissner and elastic membrane theories. We found that the relatively soft phospholipid-based MBs behave inherently differently to stiffer, polymer-based MBs [Glynos, E.; Koutsos, V.; McDicken, W. N.; Moran, C. M.; Pye, S. D.; Ross, J. A.; Sboros, V. Langmuir 2009, 25 (13), 7514-7522] and that elastic membrane theory is the most appropriate of the models tested for evaluating the Young's modulus of the phospholipid shell, agreeing with values available for living cell membranes, supported lipid bilayers, and synthetic phospholipid vesicles. Furthermore, we show that AFM F-Delta curves in combination with a suitable mechanical model can assess the shell properties of phospholipid MBs. The "effective" Young's modulus of the whole bubble was also calculated by analysis using Hertz theory. This analysis yielded values which are in agreement with results from studies which used Hertz theory to analyze similar systems such as cells.</p
Theoretical modelling of ultrasound contrast agents
No full textThis thesis compares theoretical models of ultrasound contrast agents to the acoustic response
from single Microbubbles(MBs). The acoustic response was compared using a range of driving
parameters. A rigid shelled contrast agent and a lipid shelled contrast agent were used in the
comparison.
While attempts to model the behaviour of some contrast agents at low mechanical index (MI)
have been successful at higher MI the behaviour of MBs is still not well understood. Understanding
and predicting the response ofMBs to medical ultrasound can lead to improvements in
the clinical use of MBs through improved contrast agent design or improved signal processing.
Numerical models were developed to compare to three specific cases; 1) Rigid shelled contrast
agents 2) Lipid shelled contrast agents 3) Responses from lipid shelled contrast agents that are
hit by subsequent driving pulses. Three models were used to compare to the responses from
single rigid shelled contrast agents. Two of these models have been used before and the third
was developed based on the optical observations of the responses of these rigid shelled agents
at these MI. Two shelled models were used to compare to the response of single lipid shelled
MBs. Using statistical methods the parameters defining the shell properties were found. The
parameters that gave best agreement with the lipid shelled data was then used with a model
to account for the molecular diffusion of gas from a MB and a new model to account for the
optically observed shedding of the shell from a MB to compare to the multiple response from
single MBs.
While the theoretical prediction of an acoustic response of a suspension of MBs or the radial
oscillation of single MBs has been compared before to experimental data, the successful comparison
of the acoustic response of single MBs to the theoretical prediction is the first of it’s
kind known to the author. The new theoretical model of the rigid shelled MB that was developed
in this thesis gave better agreement with the experimental data than the other previously used
models. The shell parameters of the lipid shelled MB were determined for the lowest driving
amplitude and were in agreement with those measured previously from optical observations.
Finally, the model for the shedding of the shell was shown to give quantitative agreement with
the multiple acoustic responses from single MBs. When shedding of the shell was included the
choice of constitutive equation for the shell was shown to strongly affect subsequent responses
from the MB
author-bios-SRD-19-0063.R1 – Supplemental material for The Network Structure of Police Misconduct
No full textSupplemental material, author-bios-SRD-19-0063.R1 for The Network Structure of Police Misconduct by George Wood, Daria Roithmayr and Andrew V. Papachristos in Socius</p
Bayesian Spectral Estimation Applied to Echo Signals from Nonlinear Ultrasound Scatterers
No full textThe understanding and exploitation of acoustic echo signals from nonlinear ultrasound scatterers is an active research area that aims to improve the sensitivity and specificity of diagnostic imaging. Discriminating between acoustic echoes from linear scatterers, such as tissue, and nonlinear scatterers, such as contrastmicrobubbles, based on their frequency content is also an important topic in ultrasound contrast imaging. In order to achieve these objectives, a fundamental preliminary stage is to extract information about the reflected signals in the frequency domain with high accuracy: this is essentially a feature extraction and estimation problem. In this paper, a parametric Bayesian spectral estimation method is utilised for the analysis of the backscattered echo signals from microbubbles. In contrast to existing nonparametric discrete-Fourier-transform- (DFT-) based spectral estimation techniques used in the ultrasonic literature, this method is able to estimate the number of spectral components as well as their amplitudes and frequencies. The Bayesian spectral analysis technique has improved frequency resolution compared with the DFT for short multiple-component signals at low signal-to-noise ratios. The performance of the method is demonstrated with simulated signals, as well as analysing experimentally measured echo signals from nonlinear microbubble scatterers. <br/
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Acoustic characterisation of ultrasound contrast agents at high frequency
No full textThis thesis aims to investigate the acoustic properties of ultrasound contrast agents
(UCAs) at high ultrasound frequencies. In recent years, there has been increasing
development in the use of high frequency ultrasound in the fields of preclinical,
intravascular, ophthalmology and superficial tissue imaging. Although research
studying the acoustic response of UCAs at low diagnostic ultrasonic frequencies has
been well documented, quantitative information on the acoustical properties of UCAs
at high ultrasonic frequencies is limited.
In this thesis, acoustical characterisation of three UCAs was performed using a
preclinical ultrasound scanner (Vevo 770, VisualSonics Inc., Canada).
Initially the
acoustical characterisation of five high frequency transducers was measured using a
membrane hydrophone with an active element of 0.2 mm in diameter to quantify the
transmitting frequencies, pressures and spatial beam profiles of each of the
transducers. Using these transducers and development of appropriate software, high
frequency acoustical characterisation (speed and attenuation) of an agar-based tissue
mimicking material (TMM) was performed using a broadband substitution
technique. The results from this study showed that the acoustical attenuation of
TMM varied nonlinearly with frequency and the speed of sound was approximately
constant 1548m·s-1 in the frequency range 12-47MHz.
The acoustical properties of three commercially available lipid encapsulated UCAs
including two clinical UCAs Definity (Lantheus Medical Imaging, USA) and
SonoVue (Bracco, Italy) and one preclinical UCAs MicroMarker (untargeted)
(VisualSonics, Canada) were studied using the software and techniques developed
for TMM characterisation. Attenuation, contrast-to-tissue ratio (CTR) and
subharmonic to fundamental ratio were measured at low acoustic pressures.
The
results showed that large off-resonance and resonant MBs predominantly contributed
to the fundamental response and MBs which resonated at half of the driven
frequency predominantly contributed to subharmonic response. The effect of needle
gauge, temperature and injection rate on the size distribution and acoustic properties
of Definity and SonoVue was measured and was found to have significant impacts.
Acoustic characterisations of both TMM and UCAs in this thesis extend our
understanding from low frequency to high frequency ultrasound and will enable the
further development of ultrasound imaging techniques and UCAs design specifically
for high frequency ultrasound applications
Variations on the Author
No full text“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Acoustic investigation of microbubble response to medical imaging ultrasound pulses
No full textUltrasound contrast agents have the ability to provide locally increased echogenicity, improving
the sensitivity and specificity of images. Due to the unique interaction of microbubbles with the
imaging ultrasound field, contrast ultrasonography offers both improved diagnostic techniques,
and the potential therapeutic uses of gene and drug delivery through the use of targeted agents.
By enhancing the contrast at the tissue-blood interface, an improved image of the structure of
organs can be achieved, which is useful in many areas of medical ultrasound imaging. Monitoring
the flow of contrast agent in the blood stream also offers information on the degree of
blood perfusion into an organ or microvasculature.
Present knowledge of the interaction of microbubbles with ultrasound is far from complete.
The full potential of contrast agents in improving diagnostic and therapeutic techniques has
therefore not yet been achieved. The nonlinear and dynamic properties of microbubble response
offer potentially large improvements in contrast to tissue ratio, through intelligent pulse
sequence design and/or improved signal processing. Due to various drawbacks of populations
studies, only by studying the response from single microbubbles can the interaction be fully
understood. The variations of microbubble size and shell parameters within a typical sample of
contrast agent dictate that a large number of single scatterer data are necessary to obtain information
on the variability of microbubble response, which is not possible with current optical
systems.
This thesis aims to be a contribution to the understanding of contrast behaviour in response
to medical imaging ultrasound pulses. A fully characterized microacoustic system, employing
a wide-band piezoelectric transducer from a commercial ultrasound imaging system, is introduced,
which enables the measurement of single scattering events. Single microbubble signals
from two commercially available contrast agents, Definity
R and biSphereTM, have been measured
experimentally in response to a range of clinically relevant imaging parameters. The data
has been analyzed, together with the results from appropriate theoretical models, in order to
gain physical insight into the evolution and dynamics of microbubble signals.
A theoretical model for the lipid shelled agent Definity has been developed, and the predicted
response from a real sample of single microbubbles investigated. Various characteristics of
resonant scatter have been identified, and used to distinguish resonant scatter in experimental
acoustic single bubble data for the first time. A clear distinction between the populations of
resonant and off-resonant scatter has been observed for a range of incident frequencies and
acoustic pressures. Results from consecutive imaging pulses have been used to gain understanding
of how initial size, shell material and encapsulated gas may effect the lifetime of a
microbubble signal. The response to a basic pulse sequence is also investigated, and an alternative
processing method which takes advantage of observed behaviour is presented.
Improved understanding of the contrast-ultrasound interaction will provide the basis for improved
signal processing tools for contrast enhanced imaging, with potential benefits to both
diagnostic techniques and microbubble manufacture
Využití sociálních médií v B2B prodeji
No full textTato diplomová práce se zabývá tím, jak mohou B2B obchodníci využívat sociální média v prodeji. Na základě systematické rešerše literatury, autor zjistil, že akademici, zkoumající danou problematiku, navrhují další výzkum, a to: v kterých konkrétních krocích se dají využít sociální média v prodeji (Salo, 2017). Autor se na základě toho rozhodl zjistit, jaké sociální sítě, různé technologie a pluginy se dají využít v B2B prodeji - tzv. social sellingu. Social selling se v této práci týká primárně procesu akvizice a okrajově péčí o stávající zákazníky. Autor si vybral kvalitativní průzkum pomocí 10 hloubkových polo-strukturovaných rozhovorů, aby odhalil jak, která sociální média to jsou, tak i motivaci prodejců, proč tato média používat/nepoužívat. Aby autor dodržel správnost vyhodnocení výsledků, data byla analyzována pomocí Tématické analýzy, která v této studii vykrystalizovala 2 hlavní strategické přístupy v social sellingu. Tyto přístupy (tzv. Push a Pull strategie) obsahují praktické příklady a konkrétní aktivity, které mohou prodejci využívat v každodenní praxi. Tyto výsledky jsou prezentovány s důrazem na praktičnost a jednoduchost implementace. Tvoří proto hlavní přínos autorovo výzkumu. V poslední části autor zmiňuje výzvy a manažerská doporučení, které mohou obchodníci využít v každodenním pracovním životě.This diploma thesis focuses on social media usage in B2B sales. Based on the systematic literature review conducted by the author, he has found out that recent researchers (Salo, 2017) suggest further research in the area of how and in which sales phase should various social networking sites, technologies and plugins used. To further fill this research gap, author decided to identify these social media and their usage among B2B salespeople in the so-called social selling process. The social selling process in this thesis applies mainly to acquiring new prospects and tangentially to taking care of existing clients (follow-up step). Author has chosen a qualitative research method via conducting 10 in-depth semi-structured interviews to reveal these instruments as well as motivation of a sales person on why to use social media in the selling process. The collected data was analyzed using Thematic analysis to ensure the right procedure and to identify main themes which crystalized into 2 main strategic approaches in social selling. These approaches (Push and Pull) include practical examples of concrete activities which sales people can use in their daily jobs and are presented with focus on practicality and ease of implementation. These also form the main contribution of author`s research. In the last part, author mentions challenges in social selling and recommended managerial implications for salesforce
TeX v jednoduchém unixovém prostředí
No full textsummary:Při ladění TeXového dokumentu potřebujeme mnohokrát opakovaně pouštět TeX, podívat se, jak dopadl výsledek v prohlížeči DVI nebo PDF souboru, mrknout na výpis TeXu na terminálu, podívat se případně do logu a celou činnost opakovat. V tomto článku je ukázáno, jak tuto práci dělá autor článku. Proces "editor-TeX-kuk" je zde podporován jednoduchými unixovými nástroji: bashovým skriptem texloop, který si autor pro tyto účely vytvořil, dále terminálem Xterm a jednoduchým editorem, který umí navázat na klávesovou zkratku spuštění příkazu v systému. Čtenář se zde může inspirovat a přizpůsobit tyto nástroje svým vlastním potřebám. V článku je popsána funkce skriptu texloop, dále je neformálně rozveden dlouholetý vývoj autorova vztahu k textovým editorům a konečně je zde uvedena konfigurace terminálu Xterm, aby vyhovoval českému prostředí jak v kódování ISO-8859-2, tak v kódování UTF-8. Pro kódování UTF-8 si v závěru článku vygenerujeme TeXový formát csplain.summary:By debugging a TeX document it is necessary many times repeatedly to run TeX, to look for the result in DVI or PDF file, to gander the TeX output on the terminal, or eventually to have a look in the log-file, and all that action to repeat. In the paper it is show, how this work is made by author. The process '‘'editor-TeX-look' is supported by simple Unix tools: bash script texloop, created by author for these purposes, Xterm terminal and a simple editor, which is able to link to the shortcut key the activation of a system command. The reader could be inspired with the solution and to adapt these tools to his/her own needs. In the paper the function of the texloop script is described, and further the longstanding evolution of the author's relation to text editors is informal elaborated and finally a configuration of Xterm terminal, suitable for the czech environment with both ISO-8859-2 and UTF-8 encoding is introduced. For UTF-8 encoding the TeX format csplain is generated at the end of the paper
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