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115 results on '"Kucharski, Maciej"'

1. Dimension-free estimates for positivity-preserving Riesz transforms related to Schr\'odinger operators with certain potentials

Author

Kucharski, Maciej

Subjects
Mathematics - Functional Analysis, 47D08, 42B20, 42B37
Abstract

We study the $L^\infty(\mathbb{R}^d)$ boundedness for Riesz transforms of the form ${V^{a}(-\frac12\Delta+V)^{-a}},$ where $a > 0$ and $V$ is a non-negative potential with power growth acting independently on each coordinate. We factorize the semigroup $e^{-tL}$ into one-dimensional factors, estimate them separately and combine the results to estimate the original semigroup. Similar results with additional assumption $a \leqslant 1$ are obtained on $L^1(\mathbb{R}^d)$., Comment: 13 pages

Published
2024

3. Magnetisation transfer NMR spectroscopy in a kinetic and mechanistic study of fluoride transfer from tetra-n-butylammonium difluorotriphenylsilicate (TBAT)

Author

Kucharski, Maciej M., Lloyd-Jones, Guy, and Watson, Allan

Subjects
Tetra-n-butylammonium difluorotriphenylsilicate, TBAT, fluoride transfer, FTPS, label transfer method, CEST experiments
Abstract

Tetra-n-butylammonium difluorotriphenylsilicate (ⁿBu₄NPh₃SiF₂, known as TBAT) is a pentacoordinate silicon-based fluoride source, commonly used in nucleophilic fluorinations and as an anionic initiator. The mechanism via which TBAT transfers the fluoride is not understood, but prior studies have shown that the process is rapid with respect to standard in situ NMR spectroscopic measurements. We used two ¹⁹F magnetisation transfer NMR techniques to interrogate the process directly: ¹⁹F chemical exchange saturation transfer (CEST) to examine whether TBAT dissociates into fluorotriphenylsilane (Ph₃SiF, FTPS) and tetra-n-butylammonium fluoride (ⁿBu₄NF, TBAF) in solution; and ¹⁹F inversion transfer to interrogate the kinetics and mechanism of fluoride transfer from TBAT. We first derived analytical solutions which describe the kinetics of ¹⁹F magnetisation transfer in mixtures of TBAT and the appropriate fluoride acceptors, in the inversion transfer experiments. These kinetic models enabled the interrogation of the transfer pathways in the systems, as the dependence of the magnetisation transfer rate between the spins on concentrations of the involved species varies between the proposed mechanisms in each system. CEST experiments showed that in THF and MeCN, TBAT dissociates reversibly into FTPS and TBAF. The degree of dissociation is low and the spins exchange rapidly at 300 K. Depending on the amount of adventitious water, TBAF may be involved in further equilibria or decompose. Tetra-n-butylammonium bifluoride (ⁿBu₄NF₂, TBABF) is likely formed in either case. Preliminary inversion transfer experiments showed a very rapid exchange between TBAT and FTPS in their equilibrium mixture in THF. An inherent temporal instability was observed, whereby the rate of exchange between the spins increased over time in closed systems (under N2 atmosphere). Upon screening of potential stabilising conditions, it was found that two additives, 2,6-di-tert-butylpyridine and 3 ̊Å̱ molecular sieves, reversed the trend when used concurrently, slowing down the reaction until temporal stability of exchange rate in the system was reached. The effect of concentration of FTPS under these conditions (at a constant concentration of TBAT) showed that both dissociative and direct pathways proceed in parallel. The dissociative pathway was also confirmed in the non-stabilised system by observing an initial decrease of the inversion transfer rate in a rapid titration of a concentrated solution of TBAT with small aliquots of FTPS. Inversion transfer between TBAT and 2-naphthalenyl fluorosulfate (ArOSO2F, ARSF) was detected in MeCN at 300 K, and inhibited to below the detection limit upon addition of exogeneous FTPS (~4 mM). At 335 K, progressive inhibition of the exchange was observed in solutions of TBAT and ARSF in MeCN due to decomposition of TBAT and hence formation of FTPS. Overall, we postulate that the fluoride transfer from TBAT occurs via both dissociative and direct transfer pathways proceeding in parallel, and that the contributions of these pathways are dependent upon the conditions (solvent, temperature, adventitious water, nature and concentration of the fluoride acceptor etc.). Moreover, ¹H diffusion analysis of TBAT in THF-d₈ and MeCN-d₃ indicated strong ion pairing, confirmed by the observation of nuclear Overhauser effect (NOE) between the ¹H spins of ⁿBu₄N⁺ and Ph₃SiF₂₋.

Published
2023
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5. On $L^p$ estimates for positivity-preserving Riesz transforms related to Schr\'odinger operators

Author

Kucharski, Maciej and Wróbel, Błażej

Subjects
Mathematics - Functional Analysis, Mathematics - Spectral Theory, 47D08, 42B20, 42B37
Abstract

We study the $L^{p},$ $1\leqslant p\leqslant \infty,$ boundedness for Riesz transforms of the form $V^{a}(-\frac{1}{2}\Delta+V)^{-a},$ where $a>0$ and $V$ is a non-negative potential. We prove that $V^{a}(-\frac{1}{2}\Delta+V)^{-a}$ is bounded on $L^p(\mathbb{R}^d)$ with $1< p\leqslant 2$ whenever $a\leqslant 1/p.$ We demonstrate that the $L^{\infty}(\mathbb{R}^d)$ boundedness holds if $V$ satisfies an $a$-dependent integral condition that is resistant to small perturbations. Similar results with stronger assumptions on $V$ are also obtained on $L^{1}(\mathbb{R}^d).$ In particular our $L^{\infty}$ and $L^1$ results apply to non-negative potentials $V$ which globally have a power growth or an exponential growth. We also discuss a counterexample showing that the $L^{\infty}(\mathbb{R}^d)$ boundedness may fail., Comment: 33 pages, accepted for publication in Annales de l'Institut Fourier

Published
2022

6. A dimension-free estimate on $L^2$ for the maximal Riesz transform in terms of the Riesz transform

Author

Kucharski, Maciej and Wróbel, Błażej

Subjects
Mathematics - Classical Analysis and ODEs, 42B25, 42B20, 42B15
Abstract

W prove a dimension-free estimate for the $L^2(\mathbb{R}^d)$ norm of the maximal truncated Riesz transform in terms of the $L^2(\mathbb{R}^d)$ norm of the Riesz transform. Consequently, the vector of maximal truncated Riesz transforms has a dimension-free estimate on $L^2(\mathbb{R}^d)$. We also show that the maximal function of the vector of truncated Riesz transforms has a dimension-free estimate on all $L^p(\mathbb{R}^d)$ spaces, $1

Published
2021

9. 30 GHz-voltage controlled oscillator operating at 4 K

Author

Hollmann, Arne, Jirovec, Daniel, Kucharski, Maciej, Kissinger, Dietmar, Fischer, Gunter, and Schreiber, Lars R.

Subjects
Quantum Physics, Physics - Applied Physics
Abstract

Solid-state qubit manipulation and read-out fidelities are reaching fault-tolerance, but quantum error correction requires millions of physical qubits and thus a scalable quantum computer architecture. To solve signal-line bandwidth and fan-out problems, microwave sources required for qubit manipulation might be embedded close to the qubit chip, typically operating at temperatures below 4 K. Here, we perform the first low temperature measurements of a 130 nm BiCMOS based SiGe voltage controlled oscillator. The device maintains its functionality from 300 K to 4 K. We determined the dependence of frequency and output power on temperature and magnetic field up to 5 T and measured the temperature influence on noise performance. While the output power tends to increase, the frequency shift is 3 % for temperature and 0.02 % for the field dependence, respectively, both relevant for highly coherent spin qubit applications. We observe no improvement on output noise, but increased output flickering., Comment: 5 pages, 5 figures

Published
2018
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12. Developing Laboratory Skills by Incorporating Peer-Review and Digital Badges

Author

Seery, Michael K., Agustian, Hendra Y., Doidge, Euan D., Kucharski, Maciej M., O'Connor, Helen M., and Price, Amy

Abstract

Laboratory work is at the core of any chemistry curriculum but literature on the assessment of laboratory skills is scant. In this study we report the use of a peer-observation protocol underpinned by exemplar videos. Students are required to watch exemplar videos for three techniques (titrations, distillations, preparation of standard solutions) in advance of their practical session, and demonstrate the technique to their peer, while being reviewed. For two of the techniques (titrations and distillations), the demonstration was videoed on a mobile phone, which provide evidence that the student has successfully completed the technique. In order to develop digital literacy skills, students are required to upload their videos to a video sharing site for instructor review. The activity facilitated the issuing of digital badges to students who had successfully demonstrated competency. Students' rating of their knowledge, experience, and confidence of a range of aspects associated with each technique significantly increased as a result of the activity. This work, along with student responses to questions, video access, and observations from implementation are reported in order to demonstrate a novel and useful way to incorporate peer-assessment of laboratory skills into a laboratory programme, as well as the use of digital badges as a means of incorporating and documenting transferable skills on the basis of student generated evidence.

Published
2017
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14. The KLC Cultures Synergy for Organizational Agility. Trust, Risk-Taking Attitude, and Critical Thinking as Moderators.

Author

Kucharska, Wioleta, Kucharski, Maciej, and Balcerowski, Tomasz

Subjects
*RESOURCE management, *CRITICAL thinking, *RISK management in business, *ORGANIZATIONAL learning, *DATA analysis
Abstract

Organizational agility is visible in organizational change adaptability, and it is based on the development of dynamic capabilities, strategic sensitivity of leaders, accuracy and timing of decision-making, learning aptitude, flexibility in thinking and acting, and smooth resource flow across organizations, including the knowledge resource. In such a context, this study aimed to expose how the knowledge, learning, and collaboration cultures approach (KLC) supports organizational agility when this relation is moderated by mutual trust among employees, risk-taking attitude, and critical thinking abilities. Based on the sample composed of 640 Polish knowledge workers and data analyzed with the structural equation modeling method (SEM), this study's results proved that the KLC culture synergy supports organizational agility building and that the mistakes acceptance component of learning culture is critical. Moreover, trust among workmates, risk-taking readiness, and critical thinking skills are significant mediators. The key novelty was exposed through the negative influence of a risk-taking attitude (uncertainty acceptance) on agility. Precisely, the lack of risk acceptance or, reversely, the risk-avoidance attitude supports agility. This is because agility, understood as smooth adaptability, is the effect of efficient risk management. Thanks to risk management and critical thinking, the negative impact of inaction risks can often be seen as higher than the risks of very innovative actions. The KLC approach, critical thinking, and trust among workmates support the smooth selection of risks that must be taken in today's dynamic business. Risk is inevitable. So, from this point, the essence of agility is the ability to smoothly and wisely select among risks that should be taken or avoided. In summary, agility can be considered to be the smooth selection of acceptable risks. [ABSTRACT FROM AUTHOR]

Published
2024
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15. Who is an Agile Leader? Technological vs. Non-technological Mindset Employees' Views.

Author

Kucharska, Wioleta, Balcerowski, Tomasz, Kucharski, Maciej, and Jussila, Jari

Subjects
LEADERSHIP, EMPLOYEES, RESEARCH & development, CREATIVE ability, KNOWLEDGE management
Abstract

For an agile organization to be truly agile, it must be led by agile leaders to sustain its competitiveness and continuously identify opportunities for future growth and development. Technological and non-technological mindsets can see agile leadership differently. Therefore, this study aims to explore if there is any difference in the vision of who the agile leader is in the views of knowledge workers employed in the IT and other sectors. Using a qualitative definitional/interpretive approach supported by MAXQDA software, this study revealed that from the perspective of the technological mindset, key specific to this group characteristics are diligent risk management, technology usage focus, deep understanding of needs, efficiency, and efficacy, critical thinking skills, multitasking, information and knowledge sharing, responsibility, feeling, and constant focus on improvement. Whereas from the perspective of non-technological mindsets, key specific characteristics these mindsets notice are support for employee growth, dynamism and relevance of actions taken, perfect operation on managerial paradoxes, creativity, inclusion, empathy, and self-confidence. The common characteristics that are easy to notice in both mindset types are open-minded personality, the sequential habit of revisions, reflection, and re-framing, learning from experience, wise dynamic (smooth and accurate actions), perfect change implementation skills, adaptability skills, and a positive attitude towards challenges. [ABSTRACT FROM AUTHOR]

Published
2024

16. How does the Relationship Between the Mistakes Acceptance Component of Learning Culture and Tacit Knowledge-Sharing Drive Organizational Agility? Risk as a Moderator.

Author

Kucharska, Wioleta, Balcerowski, Tomasz, Kucharski, Maciej, and Jussila, Jari

Abstract

Changes in the business context create the need to adjust organizational knowledge to new contexts to enable the organizational agile responses to secure competitiveness. Tacit knowledge is strongly contextual. This study is based on the assumption that business context determines tacit knowledge creation and acquisition, and thanks to this, the tacit knowledge-sharing processes support agility. Therefore, this study aims to expose that there is a strong link between the tacit knowledge flow across the organization and its ability to respond agilely (timely, accurately, and creatively) to contextual changes. Based on the sample composed of 640 Polish knowledge workers and data analyzed with the structural equation modeling method (SEM), this study delivers empirical evidence that tacit knowledge flow is vital for organizational agility. The obtained results confirmed that tacit knowledge sharing mediates between the mistakes acceptance component of learning culture and agility. It means agility, understood as the ability to respond agilely to contextual changes, requires being charged by new, contextual, tacit knowledge obtained thanks to trial-error actions (learning by doing) achievable thanks to breaking conventions and experimentation. Moreover, risk management skills have been proven to be one of the critical characteristics of agile organizations today. [ABSTRACT FROM AUTHOR]

Published
2024
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17. Technological vs. Non-Technological Mindsets: Learning From Mistakes, and Organizational Change Adaptability to Remote Work.

Author

Kucharska, Wioleta and Kucharski, Maciej

Subjects
ORGANIZATIONAL change, DECISION making, DIGITAL transformation, CAREER development, EMPLOYEE training
Abstract

The permanent implementation of the change in working methods, e.g., working in the virtual space, is problematic for some employees and, as a result, for management leaders. To explore this issue deeper, this study assumes that mindset type: technological vs. non-technological, may influence the organizational adaptability to change. Moreover, the key interest of this research is how non-technological mindsets adapt to remote work in the long run. Based on the OLS regression (SPSS PROCESS), authors analyze three data sets gathered via the questionnaire distributed using the CAWI method among Polish knowledge workers; the first data set was gathered in December 2019 before the COVID-19 crisis, and the next in 2021 and 2022. Findings revealed that before COVID-19, high intensity of contacts via technology-supported change adaptability only for the IT industry. Results obtained two and three years later exposed that interactions via technology also increased the change adaptability in other sectors. This study confirms that the technological environment can change the employee mindset. Nevertheless, at the same time, the adaptability process can be prolonged and complex even for highly educated knowledge workers' groups. Since there is no development without technology today - patience and long-run perspective thinking are recommended to achieve sustainable growth. It is critical. Adaptation to technologydominated virtual workspaces must continue, even if this is problematic for non-technological mindsets; abandoning this idea will only make the inevitable transformation longer and more challenging. Collective intelligence creation requires inclusion and patience instead of exclusion of those who face problems or abandonment of change when facing implementation problems rooted in mindsets. [ABSTRACT FROM AUTHOR]

Published
2023

19. Scalable integrated radar transceiver front-ends in SiGe BiCMOS technology

Author

Kucharski, Maciej Jan, Kissinger, Dietmar, and Maurer, Linus

Subjects
Millimeter wave communication systems, FMCW-Radar, SiGe, BICMOS, Mmwave, DDC 620 / Engineering & allied operations, Radar transceiver, ddc:620
Abstract

Die fortschreitende Entwicklung und Skalierung von Halbleitertechnologien hat die Implementierung von hochperformanten Radaren auf einem einzelnen Chip ermöglicht. Dies hat zu einem enormen Anstieg der Anwendung verschiedenster Radarsysteme im Alltag geführt. Silizium-basierte Technologien sind hierfür hervorragend geeignet, denn sie erlauben eine kostengünstige Realisierung solch komplexer integrierter Systeme, die hochfrequente Front-Ends sowie digitale Signalverarbeitung monolithisch vereinen. In dieser Arbeit wird der Entwurf und die Implementierung von skalierbaren Radar-Transceiver (TRX) Front-Ends in Silizium-Germanium BiCMOS Technologie präsentiert. Die kritischen Komponenten, wie Frequenzvervielfacher und Leistungsverstärker werden untersucht und Techniken, um die Leistung der Schaltkreise zu verbessern, werden vorgeschlagen. Zwei effiziente D-band Frequenzvervierfacher werden entworfen und implementiert. Dabei werden die Entwurfstechniken zur Erhöhung des Konversionsgewinns erläutert. Zwei hochperformante Ausgangsstufen mit Leistungskombinierung für das E-band und G-band werden entworfen, gefertigt und charakterisiert. Darüber hinaus wird das Problem der Signalkopplung vom Sender zum Empfänger (TX-to-RX Leakage) analysiert und eine Kompensationstechnik wird vorgeschlagen. Schließlich werden die vollständigen monostatischen und bistatischen integrierten Radar TRX für E-Band und G-Band dargestellt und mittels dedizierter FMCW Platinen evaluiert. Die Skalierbarkeit des Systems wird mit Hilfe einer 2-kanaligen E-band Radarplattform demonstriert, die den Ort in zwei Dimensionen scannen kann und eine exzellente Präzision erreicht. Die Entfernungsauflösung des Radars wird durch den Einsatz der bistatischen G-Band TRX Version mit integrierten Antennen deutlich verbessert. Die Funktionalität des TX-to-RX Leckkompensationsnetzwerkes im monostatischen TRX wird sowohl im E- als auch G-Band geprüft. Dieses Netzwerk unterdrückt effektiv das TX-to-RX Übersprechen und verbessert die Erkennung von nahen, schwach reflektierenden Objekten., Rapid development and scaling of semiconductor technologies enabled implementation of high-performance radars on a single chip which led to an enormous increase in adoption of various radar systems in everyday life. Silicon-based technologies are well suited since they offer a cost-effective realization of integrated systems comprising a high-frequency front-ends and a digital part used for signal processing. This work presents the design and implementation of scalable millimeter-wave radar transceiver (TRX) front-ends in silicon-germanium BiCMOS technology. Critical components, such as frequency multipliers and power amplifiers are analyzed and techniques are proposed to improve the performance of the circuits. Two efficient D-band frequency quadruplers are designed and implemented. Circuit techniques to enhance the conversion gain are explained. Two high-performance output stages using power combining techniques targeting E-band and G-band, respectively, are designed, fabricated and characterized. Furthermore, a transmitter-to-receiver (TX-to-RX) leakage problem in monostatic radar TRX is addressed and a compensation technique is proposed. Finally, complete monostatic and bistatic integrated radar TRXs for E-band and G-band are presented and evaluated using dedicated FMCW radar boards. Scalability of the system is demonstrated using a 2-channel E-band radar capable of two-dimensional area scanning achieving an excellent ranging precision. The range resolution is significantly enhanced by employing a G-band bistatic TRX version with on-chip antennas. Functionality of a TX-to-RX leakage compensation network is validated in both E-band and G-band monostatic TRXs effectively suppressing the crosstalk and improving detectability of near, weakly reflecting objects.

Published
2022

23. Transformational Leadership and Acceptance of Mistakes as a Source of Learning: Poland-USA Cross-Country Study.

Author

Kucharska, Wioleta, Kucharski, Maciej, and Ur Rehman, Hafeez

Subjects
TRANSFORMATIONAL leadership, ACCEPTANCE (Psychology), LEARNING, ERRORS, KNOWLEDGE workers
Abstract

This study aims to explore the influence of transformational leadership on internal innovativeness mediated by mistakes acceptance, including country and industry as factors to be considered and gender and risk-taking attitude as moderators. General findings, primarily based on the US samples (healthcare, construction, and IT industry), confirmed that transformational leadership and internal innovativeness are mediated by mistakes acceptance and strengthened by employees' risk-taking attitude. It is reflected in Polish healthcare sample. On the other hand, IT and construction industry samples revealed that a low mistakes acceptance level among risk-taking managers under transformational leadership might be their hidden form of change resistance. Regarding gender issue, this study showed that male employees driven by transformational leaders accept mistakes as a source of learning better than women, but the exceptions are healthcare and IT industries in Poland. The developed empirical model is based on a sample composed of 2,160 Polish and American knowledge workers applying OLS regression, using SPSS PROCESS macro software. [ABSTRACT FROM AUTHOR]

Published
2022

35. 240-GHz Four-Channel Power-Tuning Heterodyne Sensing Readout System With Reflection and Transmission Measurements in a 130-nm SiGe BiCMOS Technology

Author

Wang, Defu, primary, Eissa, Mohamed Hussein, additional, Schmalz, Klaus, additional, Yun, Jongwon, additional, Malignaggi, Andrea, additional, Borngraber, Johannes, additional, Kucharski, Maciej, additional, Kampfe, Thomas, additional, Seidel, Konrad, additional, Ng, Herman Jalli, additional, and Kissinger, Dietmar, additional

Published
2019
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44. Homodyne and Heterodyne Terahertz Dielectric Sensors: Prototyping and Comparison in BiCMOS Technology for Lab-on-Chip Applications

Author

Wang, Defu, primary, Schmalz, Klaus, additional, Eissa, Mohamed H., additional, Borngraber, Johannes, additional, Kucharski, Maciej, additional, Elkhouly, Mohamed, additional, Ko, Minsu, additional, Wang, Yong, additional, Ng, H.J., additional, Yun, Jongwon, additional, Tillack, Bernd, additional, and Kissinger, Dietmar, additional

Published
2018
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