Search results for "BESS"
showing 10 items of 144 documents
Stealth dicing with ultrafast Bessel beams with engineered transverse profiles
2017
International audience; We investigate high-speed glass cleaving with ultrafast laser beams with engineered transverse intensity profile. We achieve accuracy of ~ 1 µm at 25 mm/s and drastically enhance cleavability compared to standard Bessel beams.
Crack formation and cleaving of sapphire with ultrafast bessel beams
2017
Sapphire is a transparent crystalline dielectric of high hardness with many important applications, specifically to the next-generation touchscreens and to the LED growth, as substrates. However, sapphire cutting by ablative techniques is rather slow therefore fast material separation techniques are needed. Material separation by “stealth dicing” has been recently developed, it is based on material cleaving along a plane weakened by multiple ultrafast laser illuminations. This allows usually generating taper-free cutting and avoids material loss. However, the illuminated plane needs small spacing between the shot to shot (typically a few μm) and long damages inside the bulk. This requires l…
Exact Fourier expansion in cylindrical coordinates for the three-dimensional Helmholtz Green function
2009
A new method is presented for Fourier decomposition of the Helmholtz Green Function in cylindrical coordinates, which is equivalent to obtaining the solution of the Helmholtz equation for a general ring source. The Fourier coefficients of the Helmholtz Green function are split into their half advanced+half retarded and half advanced-half retarded components. Closed form solutions are given for these components in terms of a Horn function and a Kampe de Feriet function, respectively. The systems of partial differential equations associated with these two-dimensional hypergeometric functions are used to construct a fourth-order ordinary differential equation which both components satisfy. A s…
Frame-related Sequences in Chains and Scales of Hilbert Spaces
2022
Frames for Hilbert spaces are interesting for mathematicians but also important for applications in, e.g., signal analysis and physics. In both mathematics and physics, it is natural to consider a full scale of spaces, and not only a single one. In this paper, we study how certain frame-related properties of a certain sequence in one of the spaces, such as completeness or the property of being a (semi-) frame, propagate to the other ones in a scale of Hilbert spaces. We link that to the properties of the respective frame-related operators, such as analysis or synthesis. We start with a detailed survey of the theory of Hilbert chains. Using a canonical isomorphism, the properties of frame se…
Frames and weak frames for unbounded operators
2020
In 2012 G\u{a}vru\c{t}a introduced the notions of $K$-frame and of atomic system for a linear bounded operator $K$ in a Hilbert space $\mathcal{H}$, in order to decompose its range $\mathcal{R}(K)$ with a frame-like expansion. In this article we revisit these concepts for an unbounded and densely defined operator $A:\mathcal{D}(A)\to\mathcal{H}$ in two different ways. In one case we consider a non-Bessel sequence where the coefficient sequence depends continuously on $f\in\mathcal{D}(A)$ with respect to the norm of $\mathcal{H}$. In the other case we consider a Bessel sequence and the coefficient sequence depends continuously on $f\in\mathcal{D}(A)$ with respect to the graph norm of $A$.
Epigenetic differences arise during the lifetime of monozygotic twins.
2005
Monozygous twins share a common genotype. However, most monozygotic twin pairs are not identical; several types of phenotypic discordance may be observed, such as differences in susceptibilities to disease and a wide range of anthropomorphic features. There are several possible explanations for these observations, but one is the existence of epigenetic differences. To address this issue, we examined the global and locus-specific differences in DNA methylation and histone acetylation of a large cohort of monozygotic twins. We found that, although twins are epigenetically indistinguishable during the early years of life, older monozygous twins exhibited remarkable differences in their overall…
Zvaigžņotā Debess: 2017, Pavasaris (235)
2017
Contents: “ZVAIGŽŅOTĀ DEBESS” FORTY YEARS AGO: E.Mūkins. Clouds of Venus: Structure and Composition (abridged) ; J.Miezis. 3rd All-union Young Astronomers Gathering (abridged) ; DEVELOPMENTS in SCIENCE: K.Schwartz. New Discoveries in the Milky Way ; DISCOVERIES: I.Eglītis. Small Planets Get Latvian Names ; I.Pundure. Earth-mass World Revealed around Proxima Centauri ; SPACE RESEARCH and EXPLORATION: J.Jaunbergs. Mysteries of Saturn’s Clouds ; A.Slavinskis. Contribution of Estonian Student Satellite Programme ESTCube to Largest Challenges for Humanity ; R.Misa. Impossible Engine that Is likely Possible ; I.Pundure. ESO VLT to Search for Planets in Alpha Centauri System ; EARTH and COSMOS: J.…
Experimental verification of position-dependent angular-momentum selection rules for absorption of twisted light by a bound electron
2018
We analyze the multipole excitation of atoms with twisted light, i.e., by a vortex light field that carries orbital angular momentum. A single trapped $^{40}$Ca$^+$ ion serves as a localized and positioned probe of the exciting field. We drive the $S_{1/2} \to D_{5/2}$ transition and observe the relative strengths of different transitions, depending on the ion's transversal position with respect to the center of the vortex light field. On the other hand, transition amplitudes are calculated for a twisted light field in form of a Bessel beam, a Bessel-Gauss and a Gauss-Laguerre mode. Analyzing experimental obtained transition amplitudes we find agreement with the theoretical predictions at a…
New indefinite integrals from a method using Riccati equations
2018
ABSTRACTAn earlier method for obtaining indefinite integrals of special function from the second-order linear equations which define them has been reformulated in terms of Riccati equations, which ...
Zvaigžņotā Debess: 2009, Rudens (205)
2009
Contents: I.Daube. Jānis Ikaunieks ; A.Balklavs. Mountains on the Venus ; TASS and “Pravda” materials. Soviet Automatic Stations “Venera-5” and “Venera-6” Reach Venus ; A.Alksnis. Gathering of Astronomers at the University ; A.Alksnis, M.Ābele, I.Eglītis, B.Rjabovs, K.Salmiņš, I.Pundure. Directions of Scientific Research of the UL Institute of Astronomy Assessed ; D.Docenko. Meteorite Fallen in Sudan Recovered ; A.Alksnis. How Asteroids Will Disturb Observation with Extremely Large Telescopes ; M.Gills. Daily in Network with Astronomy ; I.Pundure. Arturs Balklavs and Astronomy of Latvia (continued) ; M.Sudārs. IXV – Step towards Reusable Space Vehicles ; V.Kalniņš. Hyperdrive and Heim’s Qua…