Mike Abidine Alexandre, Éric Dantras, C. Lacabanne, Émile Perez, Sophie Franceschi, Damien Coudeyre,
... composites have a poor interface. Accordingly, PEKK oligomer (PEKKo) sizing with a chemical compatibility with PEKK is ... of freeze fractures of PEKK/unsized CF, PEKK/PEKKo lab‐sized CF and PEKK/PEKKo pilot‐sized CF show that the PEKKo sizing causes an improvement of fiber/PEKK interactions, ... both methods but it is more important for PEKKo pilot sizing. In the same way, the mechanical ...
Tópico(s): Graphene research and applications
2019 - Wiley | Journal of Applied Polymer Science
Ensio Laine, Virpi Tuominen, Pekko Ilvessalo, P Kahela,
According to our observations, carbamazepine dihydrate crystals grow by the whisker mechanism (or mechanisms). The habit, the dimensions of the crystals and their rapid growth indicate this. Also the strong orientation in the X-ray diffractogram is in harmony with the whisker theory. The whisker growth explains also the rapid transition from the anhydrous form to the dihydrate one in water. Dihydrate whiskers which are loosely in the solution as well as ones fastened to the surface of the anhydrous ...
Tópico(s): Crystallization and Solubility Studies
1984 - Elsevier BV | International Journal of Pharmaceutics
Pekko Kuopanportti, Mikko Möttönen, Ville Bergholm, O.-P. Saira, Jun Zhang, K. Birgitta Whaley,
We investigate the generation of quantum operations for one-qubit systems under classical Markovian noise with a $1/{f}^{\ensuremath{\alpha}}$ power spectrum, where $2>\ensuremath{\alpha}>0$. We present an efficient way to approximate the noise with a discrete multistate Markovian fluctuator. With this method, the average temporal evolution of the qubit state operator under $1/{f}^{\ensuremath{\alpha}}$ noise can be feasibly determined from recently derived deterministic master equations. We obtain ...
Tópico(s): Quantum and electron transport phenomena
2008 - American Physical Society | Physical Review A
Pekko Ruippo, Tapio Lehtonen, N.T. Tchamov,
A voltage controlled oscillator (VCO) design strategy for extended tuning range with low phase noise at critical GSM and UMTS frequencies is applied and verified by simulations, implementation and measurements on 130 nm CMOS. The oscillator tuning range is expanded from 49.4% to 60.2% by shorting transformer secondary winding with a switch. The VCO achieves a phase noise of $-126.1~{\rm dBc/Hz}$ (switch “off”) and $-123.4~{\rm dBc/Hz}$ (switch “on”) at a 1 MHz offset from a 4 GHz and 4.8 GHz carrier while ...
Tópico(s): Electromagnetic Compatibility and Noise Suppression
2010 - IEEE Microwave Theory and Techniques Society | IEEE Microwave and Wireless Components Letters
Pekko Kuopanportti, Mikko Möttönen,
We study the splitting of multiply quantized vortices with large quantum numbers in dilute nonrotated Bose-Einstein condensates in the zero-temperature limit. The splitting is observed to result in vortex-free condensate fragments which are separated by vortex sheets. The number of these fragments is found to be equal to the angular-momentum quantum number of the Bogoliubov excitation mode responsible for the splitting, although the formulation of the fragments cannot be described by small-amplitude ...
Tópico(s): Quantum, superfluid, helium dynamics
2010 - American Physical Society | Physical Review A
Pekko Kuopanportti, Emil Lundh, Jukka Huhtamäki, Ville Pietilä, Mikko Möttönen,
Motivated by a recent demonstration of cyclic addition of quantized vorticity into a Bose-Einstein condensate, the vortex pump, we study dynamical instabilities and core sizes of giant vortices. The core size is found to increase roughly as a square-root function of the quantum number of the vortex, whereas the strength of the dynamical instability either saturates to a fairly low value or increases extremely slowly for large quantum numbers. Our studies suggest that giant vortices of very high ...
Tópico(s): Quantum, superfluid, helium dynamics
2010 - American Physical Society | Physical Review A
J. J. Lim, Roderick C. I. MacKenzie, S. Sujecki, Mahdad Sadeghi, S.M. Wang, Y.Q. Wei, Johan Gustavsson, Anders Larsson, P. Melanen, Pekko Sipilä, P. Uusimaa, A.A. George, Peter M. Smowton, E.C. Larkins,
The simulation of double quantum well (QW) GaInNAs ridge-waveguide (RW) lasers is performed over a wide range of cavity lengths and operating temperatures using a comprehensive in-house 2D laser simulator that takes into account all of the major device physics, including current spreading, capture escape processes, drift diffusion in the QW, 2D optical modes and fully resolved lasing spectra. The gain data used by the simulator were fitted to experimental gain spectra measured by the segmented contact ...
Tópico(s): Semiconductor Lasers and Optical Devices
2007 - Institution of Engineering and Technology | IET Optoelectronics
Jukka Kyynäräinen, Jaakko Saarilahti, H. Kattelus, Anu Kärkkäinen, Tor Meinander, A. Oja, Panu Pekko, Heikki Seppä, Mika Suhonen, Heikki Kuisma, Sami Ruotsalainen, Markku Tilli,
We have designed and fabricated micromechanical magnetometers intended for a 3D electronic compass which could be embedded in portable devices. The sensors are based on the Lorentz force acting on a current-carrying coil, processed on a single crystal silicon resonator, and they are operated in vacuum to reach high enough Q values. Sensors for all cartesian components of the magnetic field vector can be processed on the same chip. The vibration amplitude is detected capacitively and the resonance ...
Tópico(s): Acoustic Wave Resonator Technologies
2007 - Elsevier BV | Sensors and Actuators A Physical
Pekko Kuopanportti, Jukka Huhtamäki, Mikko Möttönen,
Recently, Freilich et al. [Science 329, 1182 (2010)] experimentally discovered stationary states of vortex dipoles, pairs of vortices of opposite circulation, in dilute Bose-Einstein condensates. To explain their observations, we perform simulations based on the Gross-Pitaevskii equation and obtain excellent quantitative agreement on the size of the stationary dipole. We also investigate how their imaging method, in which atoms are repeatedly extracted from a single condensate, affects the vortex ...
Tópico(s): Atomic and Subatomic Physics Research
2011 - American Physical Society | Physical Review A
Yongqiang Wei, Johan Gustavsson, Mahdad Sadeghi, Shumin Wang, Anders Larsson, Pekka Savolainen, P. Melanen, Pekko Sipilä,
Ridge waveguide 1.3 mum GaInNAs lasers were fabricated from high quality double quantum well material grown by molecular beam epitaxy. Short cavity (250 mum) lasers have low threshold currents and small temperature dependencies of threshold current and slope efficiency, with a characteristic temperature of the threshold current as high as 200 K. The temperature stability allows for uncooled 2.5 Gb/s operation up to temperatures as high as 110 degrees C with a constant modulation voltage and only ...
Tópico(s): Semiconductor Lasers and Optical Devices
2006 - Optica Publishing Group | Optics Express
Pekko Kuopanportti, Jukka Huhtamäki, Mikko Möttönen,
We numerically investigate vortex lattices in rotating two-component Bose-Einstein condensates in which the two components have unequal atomic masses and interact attractively with each other. For sufficiently strong attraction, the system is found to exhibit exotic ground-state structures in a harmonic trap, such as lattices having a square geometry or consisting of two-quantum vortices. The obtained states satisfy the Feynman relation, and they can be realized with current experimental techniques.
Tópico(s): Quantum, superfluid, helium dynamics
2012 - American Physical Society | Physical Review A
... in a spin-1 Bose-Einstein condensateKonstantin Tiurev, Pekko Kuopanportti and Mikko Möttönen19 February 2019 | Physical Review ...
Tópico(s): Quantum Electrodynamics and Casimir Effect
1996 - Cambridge University Press | World Scientific series in 20th century physics
Pekko Sipilä, M. Saarinen, Mircea Guină, Ville Vilokkinen, M. Toivonen, M. Pessa,
Performance characteristics of resonant cavity light-emitting diodes operating at the wavelength of 650 nm have been studied. It has been shown that a variation in device temperature significantly modifies the far-field pattern and thus the fibre coupling efficiency, due to a cavity detuning effect. Temperature dependences of output power and emission wavelength are also studied. Modulation bandwidth of >120 MHz and light power of 2 mW (cw) have been achieved for 84 µm devices driven at a 40 mA current. ...
Tópico(s): Semiconductor Quantum Structures and Devices
2000 - IOP Publishing | Semiconductor Science and Technology
Mircea Guină, S. Orsila, M. Dumitrescu, M. Saarinen, Pekko Sipilä, Ville Vilokkinen, Brendan Roycroft, Petteri Uusimaa, M. Toivonen, M. Pessa,
State-of-the-art modulation bandwidths are presented for multiquantum well resonant cavity light emitting diodes (RCLED's) emitting at 650 nm. 84-μm size epoxy coated RCLED's have a 1.4-mW (CW) output power and a small signal modulation bandwidth of 200 MHz at 40 mA bias. 150-μm diameter devices yield 3.25-mW and 150-MHz bandwidth at 70-mA bias. An open eye-diagram at 622 Mb/s achieved for the 84-μm device makes it very attractive for SONET OC-12 data communication links.
Tópico(s): Semiconductor Quantum Structures and Devices
2000 - Institute of Electrical and Electronics Engineers | IEEE Photonics Technology Letters
Tuomas Haggrén, Hua Jiang, Joona‐Pekko Kakko, Teppo Huhtio, Veer Dhaka, Esko I. Kauppinen, Harri Lipsanen,
We demonstrate efficient surface passivation of GaAs nanowires using ultrathin in-situ grown epitaxial InP and GaP capping layers, with metallo-organic vapor phase epitaxy as the growth system. The passivation increased photoluminescence intensity by three orders of magnitude compared to unpassivated nanowires, and the effect remained strong after a month of storage in air. Effective passivation was acquired over a wide range of growth temperatures, although the highest studied temperatures caused ...
Tópico(s): Semiconductor Quantum Structures and Devices
2014 - American Institute of Physics | Applied Physics Letters
Antti Jaakkola, Mika Prunnila, Tuomas Pensala, James Dekker, Panu Pekko,
Elastic constants c 11 , c 12 , and c 44 of degenerately doped silicon are studied experimentally as a function of the doping level and temperature. First-and second-order temperature coefficients of the elastic constants are extracted from measured resonance frequencies of a set of MEMS resonators fabricated on seven different wafers doped with phosphorus (carrier concentrations 4.1, 4.7, and 7.5 × 10 19 cm -3 ), arsenic (1.7 and 2.5 × 10 19 cm -3 ), or boron (0.6 and 3 × 10 19 cm -3 ). Measurements cover a temperature ...
Tópico(s): Photonic and Optical Devices
2014 - Institute of Electrical and Electronics Engineers | IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control
Jukka Liukkonen, Jukka Hirvasniemi, Antti Joukainen, Pekko Penttilä, Tuomas Virén, Simo Saarakkala, Heikki Kröger, Jukka S. Jurvelin, Juha Töyräs,
Abstract Traditional arthroscopic examination is subjective and poorly reproducible. Recently, we introduced an arthroscopic ultrasound method for quantitative diagnostics of cartilage lesions. Here we describe our investigation of the feasibility of ultrasound arthroscopy for simultaneous measurements of articular cartilage and subchondral bone. Human osteochondral samples ( n = 13) were imaged using a clinical 9-MHz ultrasound system. Ultrasound reflection coefficients (R, IRC), the ultrasound roughness index ( ...
Tópico(s): Knee injuries and reconstruction techniques
2013 - Elsevier BV | Ultrasound in Medicine & Biology
Veer Dhaka, Jani Oksanen, Hua Jiang, Tuomas Haggrén, Antti I. Nykänen, Reza Sanatinia, Joona‐Pekko Kakko, Teppo Huhtio, Marco Mattila, Janne Ruokolainen, S. Anand, Esko I. Kauppinen, Harri Lipsanen,
We report a new phenomenon related to Al-induced carrier confinement at the interface in core-shell GaAs/Al(x)Ga(1-x)As nanowires grown using metal-organic vapor phase epitaxy with Au as catalyst. All Al(x)Ga(1-x)As shells strongly passivated the GaAs nanowires, but surprisingly the peak photoluminescence (PL) position and the intensity from the core were found to be a strong function of Al composition in the shell at low temperatures. Large and systematic red shifts of up to ~66 nm and broadening ...
Tópico(s): Semiconductor materials and devices
2013 - American Chemical Society | Nano Letters
Mircea Guină, James Dekker, Antti Tukiainen, S. Orsila, M. Saarinen, M. Dumitrescu, Pekko Sipilä, Pekka Savolainen, M. Pessa,
The effect of deep level impurities on static and dynamic properties of InGaP-based light emitters grown by all-solid-source molecular-beam epitaxy is analyzed. The improvement of the output power and the decrease in modulation bandwidth induced by the burn-in process are explained by the recombination enhanced annealing of one deep level trap. This assumption is experimentally proven through comparison of small-signal analysis for resonant cavity light-emitting diodes operating at 650 nm and deep ...
Tópico(s): Spectroscopy and Laser Applications
2001 - American Institute of Physics | Journal of Applied Physics
Pekko Kuopanportti, Erin Hayward, Chu‐Chun Fu, A. Kuronen, K. Nordlund,
The behavior of hydrogen in iron and iron alloys is of interest in many fields of physics and materials science. To enable large-scale molecular dynamics simulations of systems with Fe-H interactions, we develop, based on density-functional theory calculations, an interatomic Fe-H potential in the Tersoff–Brenner formalism. The obtained analytical potential is suitable for simulations of H in bulk Fe as well as for modeling small FeH molecules, and it can be directly combined with our previously ...
Tópico(s): Nuclear Materials and Properties
2015 - Elsevier BV | Computational Materials Science
Antti Jaakkola, Mika Prunnila, Tuomas Pensala, James Dekker, Panu Pekko,
The first- and second-order temperature coefficients and the total temperature-induced frequency deviation of degenerately n-type-doped silicon resonators are modeled. Modeling is based on finite element modelling-based sensitivity analysis of various resonator geometries combined with the experimental results on doping-dependent elastic constants of n-type-doped silicon. The analysis covers a doping range from 2.4 × 10 17 to 7.5 × 10 19 cm -3 . Families of resonance modes that can be temperature compensated ...
Tópico(s): Mechanical and Optical Resonators
2015 - Institute of Electrical and Electronics Engineers | Journal of Microelectromechanical Systems
Pekko Kuopanportti, Н. В. Орлова, M. V. Miloševıć,
We show numerically that a rotating, harmonically trapped mixture of two Bose-Einstein-condensed superfluids can, contrary to its single-species counterpart, contain a multiply quantized vortex in the ground state of the system. This giant vortex can occur without any accompanying single-quantum vortices, may either be coreless or have an empty core, and can be realized in a $^{87}$Rb-$^{41}$K Bose-Einstein condensate. Our results not only provide a rare example of a stable, solitary multiquantum vortex ...
Tópico(s): Pulsars and Gravitational Waves Research
2015 - American Physical Society | Physical Review A
Léo Turquet, Joona‐Pekko Kakko, Xiaorun Zang, Liisa Naskali, Lasse Karvonen, Hua Jiang, Teppo Huhtio, Esko I. Kauppinen, Harri Lipsanen, Martti Kauranen, Godofredo Bautista,
Abstract The ability to control the optical field in the vicinity of an individual nano‐object is an obvious stepping‐stone in the tailoring of light‐matter interactions at the nanoscale. Earlier reports on tailoring light fields in the vicinity of a nano‐object have been restricted by their dependence on cumbersome optical or fabrication techniques, have relied mostly on in‐plane electric field polarizations, and have been demonstrated only for bulk materials and structures with strong in‐plane ...
Tópico(s): Photonic and Optical Devices
2016 - Wiley | Laser & Photonics Review
Veer Dhaka, Alexander Pyymaki Perros, Shagufta Naureen, Naeem Shahid, Hua Jiang, Joona‐Pekko Kakko, Tuomas Haggrén, Esko I. Kauppinen, Anand Srinivasan, Harri Lipsanen,
Low temperature (∼200 °C) grown atomic layer deposition (ALD) films of AlN, TiN, Al2O3, GaN, and TiO2 were tested for protective capping and surface passivation of bottom-up grown III-V (GaAs and InP) nanowires (NWs), and top-down fabricated InP nanopillars. For as-grown GaAs NWs, only the AlN material passivated the GaAs surface as measured by photoluminescence (PL) at low temperatures (15K), and the best passivation was achieved with a few monolayer thick (2Å) film. For InP NWs, the best passivation (∼2x ...
Tópico(s): Electronic and Structural Properties of Oxides
2016 - American Institute of Physics | AIP Advances
Fariborz Kargar, Bishwajit Debnath, Joona‐Pekko Kakko, Antti Säynätjoki, Harri Lipsanen, Denis L. Nika, Roger K. Lake, Alexander A. Balandin,
Similar to electron waves, the phonon states in semiconductors can undergo changes induced by external boundaries. However, despite strong scientific and practical importance, conclusive experimental evidence of confined acoustic phonon polarization branches in individual free-standing nanostructures is lacking. Here we report results of Brillouin-Mandelstam light scattering spectroscopy, which reveal multiple (up to ten) confined acoustic phonon polarization branches in GaAs nanowires with a diameter ...
Tópico(s): Mechanical and Optical Resonators
2016 - Nature Portfolio | Nature Communications
Н. В. Орлова, Pekko Kuopanportti, M. V. Miloševıć,
We show numerically that a harmonically trapped and coherently Rabi-coupled three-component Bose-Einstein condensate can host unconventional vortex lattices in its rotating ground state. The discovered lattices incorporate square and zig-zag patterns, vortex dimers and chains, and doubly quantized vortices, and they can be quantitatively classified in terms of a skyrmionic topological index, which takes into account the multicomponent nature of the system. The exotic ground-state lattices arise ...
Tópico(s): Physics of Superconductivity and Magnetism
2016 - American Physical Society | Physical review. A/Physical review, A
Marko Hakovirta, Veli‐Matti Tiainen, Panu Pekko,
Filtered cathodic vacuum arc (FCVA) deposition has been found to be a reliable technique for the production of high quality tetrahedral amorphous carbon films (ta-C). These coatings can be used as protective coatings for different applications ranging from cutting tools to human hip joint prosthesis. The FCVA technique is widely used in different laboratories around the world with somewhat different technical implementations. A serious disadvantage in the FCVA technique is the graphite particles that ...
Tópico(s): Metal and Thin Film Mechanics
1999 - Elsevier BV | Diamond and Related Materials
Seppo Santavirta, Reijo Lappalainen, Panu Pekko, Asko Anttila, Y T Konttinen,
Proper counterface material combinations, surface finish, and tolerances of contact surfaces are important issues in minimizing friction, wear, and corrosion of total joint prostheses. In the current study, the potential of novel amorphous diamond coatings to solve some present problems in total joint prostheses was studied by using tribological tests with a hip joint simulator and pin-on-disk testers. Based on the tests, the wear of amorphous diamond is negligible compared with conventional hip ...
Tópico(s): Orthopedic Infections and Treatments
1999 - Lippincott Williams & Wilkins | Clinical Orthopaedics and Related Research
Godofredo Bautista, Joona‐Pekko Kakko, Veer Dhaka, Xiaorun Zang, Lasse Karvonen, Hua Jiang, Esko I. Kauppinen, Harri Lipsanen, Martti Kauranen,
The three-dimensional (3D) optical fields that arise from the focusing of cylindrical vector beams (CVB) with radial and azimuthal polarizations provide new sources of contrast for optical microscopy of nano-objects. So far, these demonstrations have been restricted to two-dimensional transversal scanning, i.e., along the focal plane of interest, or use of point-like objects, i.e., single molecules and nanoparticles. Here, we demonstrate the first application of CVBs for 3D imaging of 3D nano-objects. ...
Tópico(s): Advanced Fluorescence Microscopy Techniques
2017 - Optica Publishing Group | Optics Express
Maria Kataja, Pekko Hujanen, Heini Huhtala, Kai Kaarniranta, Anja Tuulonen, Hannele Uusitalo‐Järvinen,
Aims To evaluate outcome of anti-vascular endothelial growth factor (VEGF) therapy for the treatment of neovascular age-related macular degeneration (nAMD) in the real-life setting and to compare incidence of ocular serious adverse events (SAE) after injections administered by nurses and physicians. Methods Retrospective, single-centre study. Medical records of patients receiving anti-VEGF treatment for nAMD between 2008 and 2013 with three-loading-dose regimen were evaluated. Outcome measures were ...
Tópico(s): Retinal and Optic Conditions
2017 - BMJ | British Journal of Ophthalmology