| 1. |
- Fall, Tove, 1979-, et al.
(författare)
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Relations of circulating vitamin D concentrations with left ventricular geometry and function
- 2012
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Ingår i: European Journal of Heart Failure. - : Wiley. - 1388-9842 .- 1879-0844. ; 14:9, s. 985-991
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Tidskriftsartikel (refereegranskat)abstract
- Vitamin D deficiency has been associated with risk of overt cardiovascular disease (CVD), but associations with subclinical disease are not well characterized. Hence, we examined associations of circulating vitamin D concentrations and left ventricular (LV) geometry and function by echocardiography at baseline and after 5 years in a community-based study. In the PIVUS study, we measured serum 25-dihydroxyvitamin-D (25-OH D) at age 70 and performed echocardiography including LV mass, wall thickness, end-diastolic diameter, end-systolic diameter (LVESD), left atrial diameter, fractional shortening, ejection fraction, isovolumic relaxation time, and E/A ratio at both age 70 and 75. We included 870 participants (52 women) without prior myocardial infarctions, heart failure, or prevalent valvular disease. After adjusting for potential confounders, 25-OH D at baseline was found to be significantly associated with LVESD, fractional shortening, and ejection fraction (, 0.42 mm, P 0.03; , 0.70, P 0.03; and , 0.91 P 0.01, respectively), per 1 SD increase in 25-OH D (SD 20 nmol/L) at baseline. In longitudinal analyses, vitamin D levels at baseline were not significantly associated with change in LV geometry and function after 5 years. In our community-based study among the elderly, we found higher circulating vitamin D concentrations to be associated cross-sectionally with better LV systolic function and smaller LVESD at baseline. The association persisted after adjusting for several potential confounders, including cardiovascular risk factors and calcium, phosphate, and parathyroid hormone levels. Randomized clinical trials are needed to establish firmly or refute a causal relationship between vitamin D levels and changes in LV geometry and function.
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| 2. |
- Albers, Eva, 1966, et al.
(författare)
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Selective suppression of bacterial contaminants by process conditions during lignocellulose based yeast fermentations
- 2011
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Ingår i: Biotechnology for Biofuels. - : Springer Science and Business Media LLC. - 1754-6834 .- 1754-6834. ; 4
-
Tidskriftsartikel (refereegranskat)abstract
- BackgroundContamination of bacteria in large-scale yeast fermentations is a serious problem and a threat to the development of successful biofuel production plants. Huge research efforts have been spent in order to solve this problem, but additional ways must still be found to keep bacterial contaminants from thriving in these environments. The aim of this project was to develop process conditions that would inhibit bacterial growth while giving yeast a competitive advantage.ResultsLactic acid bacteria are usually considered to be the most common contaminants in industrial yeast fermentations. Our observations support this view but also suggest that acetic acid bacteria, although not so numerous, could be a much more problematic obstacle to overcome. Acetic acid bacteria showed a capacity to drastically reduce the viability of yeast. In addition, they consumed the previously formed ethanol. Lactic acid bacteria did not show this detrimental effect on yeast viability. It was possible to combat both types of bacteria by a combined addition of NaCl and ethanol to the wood hydrolysate medium used. As a result of NaCl + ethanol additions the amount of viable bacteria decreased and yeast viability was enhanced concomitantly with an increase in ethanol concentration. The successful result obtained via addition of NaCl and ethanol was also confirmed in a real industrial ethanol production plant with its natural inherent yeast/bacterial community.ConclusionsIt is possible to reduce the number of bacteria and offer a selective advantage to yeast by a combined addition of NaCl and ethanol when cultivated in lignocellulosic medium such as wood hydrolysate. However, for optimal results, the concentrations of NaCl + ethanol must be adjusted to suit the challenges offered by each hydrolysate.
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| 3. |
- Arshamian, Artin, 1979-, et al.
(författare)
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Olfactory awareness is positively associated to odour memory
- 2011
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Ingår i: Journal of Cognitive Psychology. - : Informa UK Limited. - 2044-5911 .- 2044-592X. ; 23:2, s. 220-226
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Tidskriftsartikel (refereegranskat)abstract
- We investigated the relationship between olfactory awareness and olfactory proficiency as determined by a set of standardised olfactory tasks. Olfactory awareness was indexed by scores in questionnaires focusing on odour interest, imagery ability, and prevalence of olfactory dreams. Nineteen subjects with high and 20 subjects with low odour awareness were presented with a set of standardised olfactory tasks: odour threshold, episodic odour recognition, and odour identification. The results showed that individuals with high odour awareness excelled in odour memory and identified more odours as compared with the low awareness group. Interestingly, odour naming ability exerted no influence on odour memory. Furthermore, high odour awareness was not related to a more sensitive olfactory sensory system as determined by olfactory threshold measurements.
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| 4. |
- Baveja, Prashant, 1985, et al.
(författare)
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Impact of device parameters on thermal performance of high speed oxide confined 850 nm VCSELs
- 2012
-
Ingår i: IEEE Journal of Quantum Electronics. - 0018-9197 .- 1558-1713. ; 48:1, s. 17-26
-
Tidskriftsartikel (refereegranskat)abstract
- We study the impact of device parameters, such asinner-aperture diameter and cavity photon lifetime, on thermal rollover mechanisms in 850-nm, oxide-confined, vertical-cavity surface-emitting lasers (VCSELs) designed for high-speed operation. We perform measurements on four different VCSELs of different designs and use our empirical thermal model for calculating the power dissipated with increasing bias currents through various physical processes such as absorption within the cavity, carrier thermalization, carrier leakage, spontaneous carrier recombination, and Joule heating. When reducing the topmirror reflectivity to reduce internal optical absorption loss we find an increase of power dissipation due to carrier leakage. There is therefore a trade-ff between the powers dissipated owing to optical absorption and carrier leakage in the sense that overcompensating for optical absorption enhances carrier leakage (and vice versa). We further find that carrier leakage places the ultimate limit on the thermal performance for this entire class ofdevices. Our analysis yields useful design optimization strategies for mitigating the impact of carrier leakage and should thereby prove useful for the performance enhancement of 850-nm, highspeed, oxide-confined VCSELs.
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| 5. |
- Baveja, P. P., et al.
(författare)
-
Assessment of VCSEL thermal rollover mechanisms from measurements and empirical modeling
- 2011
-
Ingår i: Optics Express. - 1094-4087 .- 1094-4087. ; 19:16, s. 15490-15505
-
Tidskriftsartikel (refereegranskat)abstract
- We use an empirical model together with experimental measurements for studying mechanisms contributing to thermal rollover in vertical-cavity surface-emitting lasers (VCSELs). The model is based on extraction of the temperature dependence of threshold current, internal quantum efficiency, internal optical loss, series resistance and thermal impedance from measurements of output power, voltage and lasing wavelength as a function of bias current over an ambient temperature range of 15-100 degrees C. We apply the model to an oxide-confined, 850-nm VCSEL, fabricated with a 9-mu m inner-aperture diameter and optimized for highspeed operation, and show for this specific device that power dissipation due to linear power dissipation (sum total of optical absorption, carrier thermalization, carrier leakage and spontaneous carrier recombination) exceeds power dissipation across the series resistance (quadratic power dissipation) at any ambient temperature and bias current. We further show that the dominant contributors to self-heating for this particular VCSEL are quadratic power dissipation, internal optical loss, and carrier leakage. A rapid reduction of the internal quantum efficiency at high bias currents (resulting in high temperatures) is identified as being the major cause of thermal rollover. Our method is applicable to any VCSEL and is useful for identifying the mechanisms limiting the thermal performance of the device and to formulate design strategies to ameliorate them.
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| 6. |
- Baveja, P. P., et al.
(författare)
-
Impact of photon lifetime on thermal rollover in 850-nm high-speed VCSELs
- 2012
-
Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. - 9780819489197 ; 8276
-
Konferensbidrag (refereegranskat)abstract
- We present an empirical thermal model for VCSELs based on extraction of temperature dependence of macroscopic VCSEL parameters from CW measurements. We apply our model to two, oxide-confined, 850-nm VCSELs, fabricated with a 9-mu m inner-aperture diameter and optimized for high-speed operation. We demonstrate that for both these devices, the power dissipation due to linear heat sources dominates the total self-heating. We further show that reducing photon lifetime down to 2 ps drastically reduces absorption heating and improves device static performance by delaying the onset of thermal rollover. The new thermal model can identify the mechanisms limiting the thermal performance and help in formulating the design strategies to ameliorate them.
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| 7. |
- Davani, Hooman A., et al.
(författare)
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Polarization investigation of a tunable high-speed short-wavelength bulk-micromachined MEMS-VCSEL
- 2012
-
Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. - 9780819489197 ; 8276, s. Art. no. 82760T-
-
Konferensbidrag (refereegranskat)abstract
- We report the investigation of the state of polarization (SOP) of a tunable vertical-cavity surface-emitting laser (VCSEL) operating near 850 nm with a mode-hop free single-mode tuning range of about 12 nm and an amplitude modulation bandwidth of about 5 GHz. In addition, the effect of a sub-wavelength grating on the device and its influence on the polarization stability and polarization switching has been investigated. The VCSEL with an integrated sub-wavelength grating shows a stable SOP with a polarization mode suppression ratio (PMSR) more than 35 dB during the tuning.
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| 8. |
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| 9. |
- Fredriksson, Nils Johan, 1979-, et al.
(författare)
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Systematic analysis of noncoding somatic mutations and gene expression alterations across 14 tumor types
- 2014
-
Ingår i: Nature Genetics. - : Nature Publishing Group. - 1061-4036 .- 1546-1718. ; 46:12, s. 1258-1263
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Tidskriftsartikel (refereegranskat)abstract
- Somatic mutations in noncoding sequences are poorly explored in cancer, a rare exception being the recent identification of activating mutations in TERT regulatory DNA. Although this finding is suggestive of a general mechanism for oncogene activation, this hypothesis remains untested. Here we map somatic mutations in 505 tumor genomes across 14 cancer types and systematically screen for associations between mutations in regulatory regions and RNA-level changes. We identify recurrent promoter mutations in several genes but find that TERT mutations are exceptional in showing a strong and genome-wide significant association with increased expression. Detailed analysis of TERT across cancers shows that the strength of this association is highly variable and is strongest in copy number stable cancers such as thyroid carcinoma. We additionally propose that TERT promoter mutations control expression of the nearby gene CLPTM1L. Our analysis provides a detailed pan-cancer view of TERT transcriptional activation but finds no clear evidence for frequent oncogenic promoter mutations beyond TERT.
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| 10. |
- Gierl, Christian, et al.
(författare)
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Tuneable VCSEL aiming for the application in interconnects and short haul systems
- 2011
-
Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. - 9780819484963 ; 7959
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Widely tunable vertical cavity surface emitting lasers (VCSEL) are of high interest for optical communications, gas spectroscopy and fiber-Bragg-grating measurements. In this paper we present tunable VCSEL operating at wavelength around 850 nm and 1550 nm with tuning ranges up to 20 nm and 76 nm respectively. The first versions of VCSEL operating at 1550 nm with 76 nm tuning range and an output power of 1.3mW were not designed for high speed modulation, but for applications where only stable continious tuning is essential (e.g. gas sensing). The next step was the design of non tunable VCSEL showing high speed modulation frequencies of 10 GHz with side mode supression ratios beyond 50 dB. The latest version of these devices show record output powers of 6.7mW at 20 °C and 3mW at 80 °C. The emphasis of our present and future work lies on the combination of both technologies. The tunable VCSEL operating in the 850 nm-region reaches a modulation bandwidth of 5.5GHz with an output power of 0.8mW.
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| 11. |
- Haglund, Erik, 1985, et al.
(författare)
-
25 Gbit/s transmission over 500 m multimode fibre using 850 nm VCSEL with integrated mode filter
- 2012
-
Ingår i: Electronics Letters. - : Institution of Engineering and Technology (IET). - 1350-911X .- 0013-5194. ; 48:9, s. 517-518
-
Tidskriftsartikel (refereegranskat)abstract
- An integrated mode filter in the form of a shallow surface relief was used to reduce the spectral width of a high-speed 850 nm vertical-cavity surface-emitting laser (VCSEL). The mode filter reduced the RMS spectral width from 0.9 to 0.3 nm for a VCSEL with an oxide aperture as large as 5 mu m. Because of reduced effects of chromatic and modal fibre dispersion, the mode filter significantly increases the maximum error-free (bit error rate
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| 12. |
- Haglund, Erik, 1985, et al.
(författare)
-
High-speed lasers for optical interconnects
- 2012
-
Ingår i: Swedish Optics and Photonics Days 2012.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In the era of cloud computing, with services such as video streaming, social networking, and online storage and file sharing, the demand for online data processing and storage capacity is growing rapidly. These services are hosted in huge data centers that need not only fast servers but also fast communication between servers. Because copper cables have high attenuation at high frequencies, the most promising solution is to use fiber optical links (called optical interconnects) to connect different parts of the data center. Today, gallium arsenide-based vertical-cavity surface-emitting lasers (VCSELs) emitting at 850 nm are the standard light source in transmitters used in commercially available optical interconnects, operating at up to 14 Gbit/s with a link length of up to 300 m. These lasers have the advantages of low power consumption, fast direct modulation at low currents, and low-cost manufacturing. To keep up with the demand of increasing optical interconnect capacity, the Photonics Laboratory at Chalmers university of Technology is conducting research into improving the speed, reach and capacity of VCSELs for optical interconnects.
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| 13. |
- Haglund, Erik, 1985, et al.
(författare)
-
Low Spectral Width High-Speed VCSELs
- 2011
-
Ingår i: International Nano-Optoelectronic Workshop (iNOW).
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The transmission distance of high-speed multimode 850 nm VCSELs is currently limited by modal dispersion. A design and process to fabricate high-speed VCSELs with a reduced spectral width using a surface relief technique are presented.
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| 14. |
- Haglund, Erik, 1985, et al.
(författare)
-
Mode-filtered semiconductor lasers enable longer-reach optical interconnects
- 2012
-
Ingår i: SPIE Newsroom. - : SPIE-Intl Soc Optical Eng. - 1818-2259.
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- An integrated mode filter significantly decreases the spectral width of conventional short-wavelength vertical-cavity surface-emitting lasers, promising longer optical interconnects for future data centers.
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| 15. |
- Haglund, Erik, 1985, et al.
(författare)
-
Reducing the spectral width of high speed oxide confined VCSELs using an integrated mode filter
- 2012
-
Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. - 9780819489197 ; 8276, s. Article Number: 82760L-
-
Konferensbidrag (refereegranskat)abstract
- We have reduced the spectral width of high speed oxide confined 850 nm VCSELs using a shallow surface relief for suppression of higher order transverse modes. The surface relief acts as a mode filter by introducing a spatially varying and therefore mode selective loss. The VCSEL employs multiple oxide layers for reduced capacitance which leads to a strong index guiding and a large spectral width in the absence of a mode filter. With an appropriate choice of surface relief parameters, the RMS spectral width for a 5 jam oxide aperture VCSEL is reduced from 0.6 to 0.3 nm. The small signal modulation bandwidth is 19 GHz. Due to reduced effects of chromatic and modal fiber dispersion, the maximum error-free (bit-error-rate
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| 16. |
- Karlsson, Johan, 1979-, et al.
(författare)
-
Kinetic Considerations of Gas-Phase Adsorption of Growth Species on the c-BN(100) Surface
- 2014
-
Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 564, s. 246-252
-
Tidskriftsartikel (refereegranskat)abstract
- The cubic phase of boron nitride (c-BN) is an extremely promising multifunctional material. However, to exploit all possible applications, a successful route for large area chemical vapor deposition (CVD) of c-BN films is required. Adsorption of gaseous growth species onto the c-BN surface is one of the key elementary reactions in CVD growth of c-BN. In the present study, adsorption of BHx, BFx, and NHx species (x = 0, 1, 2, 3) onto the B- and N-terminated c-BN(100) surfaces has been investigated using density functional theory (DFT) calculations. It was found that adsorption of BHx is an activation less process.
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| 17. |
- Karlsson, Johan, 1979-
(författare)
-
Theoretical Routes for c-BN Thin Film Growth
- 2013
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Cubic boron nitride (c-BN) has been in focus for several years due to its interesting properties. The possibility for large area chemical vapor deposition (CVD) is a requirement for the realization of these different properties in various applications. Unfortunately, there are at present severe problems in the CVD growth of c-BN. The purpose with this research project has been to theoretically investigate, using density functional theory (DFT) calculations, the possibility for a layer-by-layer CVD growth of c-BN. The results, in addition with experimental work by Zhang et al.57, indicate that plasma-enhanced atomic layer deposition (PEALD), using a BF3-H2-NH3-F2 pulse cycle and a diamond substrate, is a promising method for deposition of c-BN films. The gaseous species will decompose in the plasma and form BFx, H, NHx, and F species (x = 0, 1, 2, 3). The H and F radicals will uphold the cubic structure by completely hydrogenate, or fluorinate, the growing surface. Surface radical sites will appear during the growth process as a result of atomic H, or F, abstraction reactions. However, introduction of energy (e.g., ionic bombardment) is probably necessary to promote removal of H from the surface. The addition of NHx growth species (x = 0, 1, 2) to the B radical sites, and BFx growth species (x = 0, 1, 2) to N radical sites, will then result in a continuous growth of c-BN.
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| 18. |
- Karlsson, Johan, 1979-
(författare)
-
Theoretical Routes for c-BN Thin Film Growth
- 2013
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- c-BN has been in focus for several years due to its interesting properties. The possibility for large area CVD is a requirement for the realization of these different properties in various applications. Unfortunately, there are at present severe problems in the CVD growth of c-BN. The purpose with this research project has been to theoretically investigate, using DFT calculations, the possibility for a layer-by-layer CVD growth of c-BN. It could be established that, PEALD, using a BF3-H2-NH3-F2 pulse cycle and a diamond substrate, is a promising method for deposition of c-BN films. The gaseous species will decompose in the plasma and form BFx, H, NHx, and F species (x = 0, 1, 2, 3). The H and F radicals will uphold the cubic structure by completely hydrogenate, or fluorinate, the growing surface. However, surface radical sites will appear during the growth process as a result of atomic H, or F, abstraction reactions. The addition of NHx growth species (x = 0, 1, 2) to B radical sites, and BFx growth species (x = 0, 1, 2) to N radical sites, will then result in a continuous growth of c-BN.
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| 19. |
- Kögel, Benjamin, 1979, et al.
(författare)
-
Integrated MEMS-tunable VCSELs for reconfigurable optical interconnects
- 2012
-
Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. - 9780819489197 ; 8276, s. Article Number: 82760Q-
-
Konferensbidrag (refereegranskat)abstract
- A simple and low-cost technology for tunable vertical-cavity surface-emitting lasers (VCSELs) with curved movable micromirror is presented. The micro-electro-mechanical system (MEMS) is integrated with the active optical component (so-called half-VCSEL) by means of surface-micromachining, using a reflown photoresist droplet as sacrificial layer. The technology is demonstrated for electrically pumped, short-wavelength (850nm) tunable VCSEts. Fabricated devices with 10 mu m oxide aperture are singlemode with sidemode suppression >35 dB, tunable over 24 mit with output power up to 0.5 mW, and have a beam divergence angle
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| 20. |
- Kögel, Benjamin, 1979, et al.
(författare)
-
Integrated MEMS-Tunable VCSELs Using a Self-Aligned Reflow Process
- 2012
-
Ingår i: IEEE Journal of Quantum Electronics. - 0018-9197 .- 1558-1713. ; 48:2, s. 144-152
-
Tidskriftsartikel (refereegranskat)abstract
- A simple microelectromechanical systems technology for wafer-scale integration of tunable vertical-cavity surface-emitting lasers (VCSELs) is presented. The key element is a self-aligned reflow process to form photoresist droplets, which serve as sacrificial layer and preform for a curved micromirror. Using a 3-D electromagnetic model, the half-symmetric cavity is optimized for singlemode emission. The technology is demonstrated for electrically pumped, short-wavelength (850 nm) tunable VCSELs, but is transferable to other wavelengths and material systems. Fabricated devices with 10 mu m large current aperture are singlemode and tunable over 24 nm. An improved high-speed design with reduced parasitic capacitance enables direct modulation with 3dB-bandwidths up to 6 GHz and data transmission at 5Gbit/s. Small signal analysis shows that the intrinsic parameters (resonance frequency and damping) are wavelength dependent through the differential gain.
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| 21. |
- Kögel, Benjamin, 1979, et al.
(författare)
-
Integrated MEMS-tunable VCSELs with high modulation bandwidth
- 2011
-
Ingår i: Electronics Letters. - : Institution of Engineering and Technology (IET). - 1350-911X .- 0013-5194. ; 47:13, s. 764-756
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Tidskriftsartikel (refereegranskat)abstract
- The modulation bandwidth of micromachined tunable VCSELs is typically limited by the parasitic capacitance associated with the large mesa platform for the movable mirror. Presented is a simple technology for wafer-scale integration of tunable VCSELs with low mesa capacitance and high modulation bandwidth. Small signal measurements show a 3dB bandwidth of up to 6 GHz over a tuning range of 18 nm. Digital modulation is demonstrated with error-free data transmission at 5 Gbit/s and eye diagrams at 10 Gbit/s.
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| 22. |
- Kögel, Benjamin, 1979, et al.
(författare)
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Integrated Tunable VCSELs With Simple MEMS Technology
- 2010
-
Ingår i: Semiconductor Laser Conference (ISLC), 2010 22nd IEEE International. - 0899-9406. - 9781424456833
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Konferensbidrag (refereegranskat)abstract
- A simple MEMS technology for wafer-scale fabrication of tunable VCSELs is presented. Reflown photo-resist droplets serve as preform for making curved movable micro-mirrors. First devices show a tuning range of 15 nm with mW-output power.
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| 23. |
- Kögel, Benjamin, 1979, et al.
(författare)
-
Singlemode tunable VCSELs with integrated MEMS technology
- 2011
-
Ingår i: European Conference on Laser and Electro-Optics (CLEO/Europe).
-
Konferensbidrag (refereegranskat)abstract
- A simple MEMS technology for wafer-scale integration of short-wavelength tunable VCSELs is presented. Using a 3D model the half-symmetric cavity is optimized for singlemode emission from 10 μm large apertures over 12 nm tuning range.
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| 24. |
- Larsson, Anders, 1957, et al.
(författare)
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High-speed tunable and fixed-wavelength VCSELs for short-reach optical links and interconnects
- 2012
-
Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. - 9780819489197 ; 8276, s. Article Number: 82760H-
-
Konferensbidrag (refereegranskat)abstract
- This paper presents a review of recent work on high speed tunable and fixed wavelength vertical cavity surface emitting lasers (VCSELs) at Chalmers University of Technology. All VCSELs are GaAs-based, employ an oxide aperture for current and/or optical confinement, and emit around 850 nm. With proper active region and cavity designs, and techniques for reducing capacitance and thermal impedance, our fixed wavelength VCSELs have reached a modulation bandwidth of 23 GHz, which has enabled error-free 40 Gbps back-to-back transmission and 35 Gbps transmission over 100 m of multimode fiber. A MEMS-technology for wafer scale integration of tunable high speed VCSELs has also been developed. A tuning range of 24 nm and a modulation bandwidth of 6 GHz have been achieved, enabling error-free back-to-back transmission at 5 Gbps.
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| 25. |
- Larsson, Anders, 1957, et al.
(författare)
-
High speed VCSELs for optical interconnects
- 2012
-
Ingår i: Conference Proceedings - International Conference on Indium Phosphide and Related Materials. - 1092-8669. - 9781467317252 ; , s. 269-272
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Konferensbidrag (refereegranskat)abstract
- This paper presents an overview of our recent work on high speed, oxide confined, 850 nm vertical cavity surface emitting lasers (VCSELs). With proper active region and cavity designs, and techniques for reducing capacitance and thermal impedance, we have reached a modulation bandwidth of 23 GHz and demonstrated 40 Gbps transmission. Using an integrated mode filter for reducing the spectral width we have extended the reach on multimode fiber at 25 Gbps from 100 to 500 m. Improved link capacity was also demonstrated using a more spectrally efficient multi-level modulation format (4-PAM). Finally, a MEMS-technology for wafer scale integration of tunable high speed VCSELs was developed, enabling a tuning range of 24 nm, a 6 GHz modulation bandwidth, and 5 Gbps transmission.
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| 26. |
- Larsson, Anders, 1957, et al.
(författare)
-
High speed VCSELs for short reach communication
- 2011
-
Ingår i: Semiconductor Science and Technology. - 1361-6641 .- 0268-1242. ; 26:1, s. 014017-1-5-
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Tidskriftsartikel (refereegranskat)abstract
- We present the design of a high-speed 850 nm multimode vertical cavity surface-emitting laser (VCSEL) and demonstrate record performance in terms of small signal modulation bandwidth (23 GHz) and error-free operation at high bit rates (40 Gb s−1). The large bandwidth was enabled by an active region design for large differential gain and small gain compression, a low reflectivity top mirror for photon lifetime reduction and multiple oxide layers for a reduction of the capacitance. Error-free operation at 40 Gb s−1 was achieved in a back-to-back configuration with less than 0 dBm of received optical power.
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| 27. |
- Larsson, Johan, 1979-, et al.
(författare)
-
Control charts as an early warning system for workplace health outcomes
- 2011
-
Ingår i: Work. - 1051-9815 .- 1875-9270. ; 39:4, s. 409-425
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Tidskriftsartikel (refereegranskat)abstract
- Introduction: Statistical Process Control (SPC) charts have not been widely used to monitor workplace health and work environments. This research and effort to develop a more accurate and easy to use management control system for employee health is important from a humanistic, societal and economic standpoint, as well as complying with laws that regulate work environments. Objective: The purpose of the study is to design and discuss control charts as an early warning system for workplace health outcomes to promote workplace health management. Another purpose is to discuss relevant factors in the concept of the Out-of-Control Action Plan (OCAP) as a response when a chart warns that the workplace process may be malfunctioning. Participants: Two Swedish organizations were selected as case study organizations: a department at a university and an elderly care operation in a municipality. Methods: This study was explorative and should be seen as a starting point in learning how to use control charts for workplace health management. Self-assessed general health and new sick-cases per employee were selected as indicators for the control charts. Results: An integrated early warning system with Cumulative Sums-and Shewhart-charts are presented to show a possible method as to how an early warning system can be structured through the use of statistical control charts. Conclusions: The conclusion of this study is that control charts, along with well-designed implementation, make up a powerful and useable managerial early-warning system which promotes workplace health and helps to prevent sickness absence.
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| 28. |
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| 29. |
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| 30. |
- Larsson, Johan, 1979-, et al.
(författare)
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Leadership behaviour in successful organisations: Universal or situation-dependent? : Universal or situational-dependent?
- 2010
-
Ingår i: Total Quality Management and Business Excellence. - London : Taylor & Francis. - 1478-3363 .- 1478-3371. ; 21:3, s. 317-334
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Tidskriftsartikel (refereegranskat)abstract
- Leadership behaviour has a critical role in the creation of successful organisations. This article reviews dimensions of leadership behaviour theory and their relationship to effectiveness, productivity, quality, health and job satisfaction in organisations. The article has two purposes: (1) to identify and summarise leadership behaviours common among successful organisations; and (2) to use these common elements to discuss those theoretical implications which concern situational aspects of successful leadership behaviour. The successful organisations studied for this work were two manufacturing companies, one hospital and one retail operation. The case studies were performed in connection with two leadership research projects. They focused on quality work, effectiveness, working environment, subordinate health and perceptions of the leadership. The common leadership behaviours were explored using a comparative qualitative method. The identified common leadership behaviours were then analysed in relation to the three-dimensional leadership behaviour theory (change-, structure- and relation-orientation) to explore distributions between dimensions. Nine common groups of behaviours were identified and described. The qualitative analyses showed that the identified behaviours were in all three behaviour dimensions. Also evident was that relation-oriented leadership behaviour was by far the strongest of the three. The conclusion is that a successful leader uses high relation-orientation as a base. At the same time, this successful leader uses all three behaviour dimensions. The two additional dimensions of structure- and change-orientation can be altered by leaders according to situational factors. This conclusion implies that successful leadership behaviour includes both universal and contingency elements.
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| 31. |
- Larsson, Johan, 1979-
(författare)
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Leadership for Quality, Effectiveness and Health
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Leadership, quality, effectiveness and health are important factors in the achievement of organisational success. Three questions are addressed to study these elements: 1. How do leadership values relate to leadership behaviours, quality methodologies and health in organisations? 2. How do leadership behaviours relate to effectiveness and health in organisations? 3. How can leadership tools be designed and used to promote health in organisations? The research is based on five studies from three research projects. This research is reported in five papers. Study I concerned eight organisations in the middle of Sweden; the focus was on leadership values and behaviours. Study II concerned three successful organisations that received the award, ‘Sweden’s number one workplace’. Focus in this study was mainly on leadership behaviours. Study III combined results from Studies I and II with a focus on successful leadership behaviours. Study IV concerned the eight organisations in Study I. A leadership tool in the form of a Plan-Do-Study-Act (PDSA) model was developed and evaluated. Study V was of two organisations in Sweden; the focus in that work was on the use of a leadership tool control chart designed to give managers statistically valid early warning signals about health in their organisations. Theory X and Y together with the three-dimensional leadership behaviour theory were used to assess leadership values and behaviours. The theory surrounding PDSA and control charts were used to develop leadership tools. The dimension of health is defined from a salutogenic humanistic perspective; which emphasizes individual well-being. The dimension of quality is defined as the ability to satisfy or exceed needs and expectations. Effectiveness is defined as the extent to which externally and internally defined objectives are fulfilled. Both qualitative and quantitative research methods were used. Interviews, seminars with employees, collection of human resource and effectiveness figures, and questionnaires completed by managers and subordinates were used to collect data. Managers with more Theory Y-oriented leadership values were rated by subordinates as high concerning quality methodologies and leadership behaviour dimensions. The subordinates of these managers tended to be healthier. Two of the studies identified common groups of leadership behaviours in effective and healthy organisations: strategy and vision, communication and information, authority and responsibility, learning culture, worker conversations, plainness and simplicity, humanity and trust, walking around and reflective personal leadership. These leadership behaviours fit into a leadership profile where all three of the dimensions of structure, relation and change are present. Of the three, the relation dimension is strongest and concluded to be a universal dimension. The developed PDSA model seems to be a leadership tool that influences both leadership values and behaviour, particularly in the area of relation-oriented leadership behaviours. An early warning system built on CUSUM- and Shewhartcharts concerning the health indicators of self-assessed general health and new sickcases per employee was also found to be a powerful and usable leadership tool. For future research, the explorative research findings can be quantitatively tested using representative and preferably cross-national data, with a longitudinal design.
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| 32. |
- Safaisini, Rashid, 1981, et al.
(författare)
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High-Speed 850 nm Quasi-Single Mode VCSELs for Extended Reach Optical Interconnects
- 2013
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Ingår i: Journal of Optical Communications and Networking. - 1943-0620 .- 1943-0639. ; 5:7, s. 686-695
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents recent results on high-speed, quasi-single-mode, 850 nm vertical-cavity surface-emitting lasers (VCSELs) with a narrow spectral width for extended-reach optical interconnects. The top mirror reflectivity is adjusted for high output power, slope efficiency, and small signal modulation bandwidth. An oxide confined VCSEL with an ∼3 μm aperture diameter delivers 2 mW of output power and reaches a resonance frequency as high as 25 GHz and a modulation bandwidth exceeding 20 GHz. A small K-factor of 0.17 ns and a large D-factor of 17.3 GHz/mA1/2, extracted from the VCSEL modulation response, along with the improved DC and modal properties enable energy-efficient data transmission at high bit rates over long-distance multimode fiber. Error-free transmission at bit rates exceeding 20 Gbits/s over 1.1 km of OM4 fiber is demonstrated and shown to be limited mainly by the photoreceiver bandwidth. A theoretical investigation of the dependence of link performance on photoreceiver bandwidth is also presented.
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| 33. |
- Westbergh, Petter, 1981, et al.
(författare)
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40 Gbit/s error-free operation of oxide-confined 850 nm VCSEL
- 2010
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Ingår i: Electronics Letters. - : Institution of Engineering and Technology (IET). - 1350-911X .- 0013-5194. ; 46:14, s. 1014-1015
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Tidskriftsartikel (refereegranskat)abstract
- Error-free transmission is demonstrated at bit rates up to 40 Gbit/s in a back-to-back configuration and up to 35 Gbit/s over 100 m multimode fibre using a directly modulated oxide confined 850 nm vertical cavity surface emitting laser.
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| 34. |
- Westbergh, Petter, 1981, et al.
(författare)
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850 nm VCSEL Operating Error-Free at 40 Gbit/s
- 2010
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Ingår i: Semiconductor Laser Conference (ISLC), 2010 22nd IEEE International. - 0899-9406. - 9781424456833 ; , s. 154 - 155
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Konferensbidrag (refereegranskat)abstract
- We report on speed enhancement of 850 nm oxide confined VCSELs by photon lifetime reduction and demonstrate a 23 GHz modulation bandwidth and error-free operation at 40 Gbit/s.
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| 35. |
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| 36. |
- Westbergh, Petter, 1981, et al.
(författare)
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High-speed 850 nm VCSELs with 28 GHz modulation bandwidth operating error-free up to 44 Gbit/s
- 2012
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Ingår i: Electronics Letters. - : Institution of Engineering and Technology (IET). - 1350-911X .- 0013-5194. ; 48:18, s. 1145-U178
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Tidskriftsartikel (refereegranskat)abstract
- A new generation of high-speed oxide confined 850 nm vertical cavity surface-emitting lasers is presented. A record high modulation bandwidth of 28 GHz is achieved and error-free data transmission at bit-rates up to 44 Gbit/s is demonstrated.
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| 37. |
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| 38. |
- Westbergh, Petter, 1981, et al.
(författare)
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Higher speed VCSELs by photon lifetime reduction
- 2011
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. - 9780819484895 ; 7952
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The impedance characteristics and the effects of photon lifetime reduction on the performance of high-speed 850 nm VCSELs are investigated. Through S 11 measurements and equivalent circuit modeling we show that the parasitic mesa capacitance can be significantly reduced by using multiple oxide layers. By performing a shallow surface etch (25 - 55 nm) on the fabricated VCSELs, we are able to reduce the photon lifetime by up to 80% and thereby significantly improve both static and dynamic properties of the VCSELs. By optimizing the photon lifetime we are able to enhance the 3dB modulation bandwidth of 7 μm oxide aperture VCSELs from 15 GHz to 23 GHz and finally demonstrate errorfree transmission at up to 40 Gbit/s.
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| 39. |
- Westbergh, Petter, 1981, et al.
(författare)
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Impact of Photon Lifetime on High-Speed VCSEL Performance
- 2011
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Ingår i: IEEE Journal of Selected Topics in Quantum Electronics. - 1558-4542 .- 1077-260X. ; 17:6, s. 1603-1613
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the impact of reduced photon lifetime on the static and dynamic performance of high-speed, oxide-confined 850-nm vertical-cavity surface-emitting lasers (VCSELs). The photon lifetime is reduced by a shallow-surface etch that lowers the reflectivity of the top mirror. From an analysis of the dependence of slope efficiency on mirror loss (etch depth) and temperature, we deduce values for the internal quantum efficiency and the internal optical loss and their dependencies on temperature. From an analysis of the dependence of the small-signal-modulation response on photon lifetime (etch depth) and temperature, we deduce values for differential gain and gain compression, and their dependencies on photon lifetime and temperature. We find a tradeoff between high resonance frequency and low damping for speed enhancement, leading to an optimum photon lifetime close to 3 ps for this particular VCSEL design that enables a modulation bandwidth of 23 GHz and error-free transmission at 40 Gb/s.
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| 40. |
- Westbergh, Petter, 1981, et al.
(författare)
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Speed enhancement of VCSELs by photon lifetime reduction
- 2010
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Ingår i: Electronics Letters. - : Institution of Engineering and Technology (IET). - 1350-911X .- 0013-5194. ; 46:13, s. 938-940
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Tidskriftsartikel (refereegranskat)abstract
- The dependence of the performance of high-speed 850 nm vertical cavity surface-emitting lasers (VCSELs) on photon lifetime is investigated. The photon lifetime is controlled by shallow surface etching. It is demonstrated that a reduction of photon lifetime by similar to 50% leads to a significant improvement of efficiency and speed. A record high 3 dB bandwidth of 23 GHz is achieved.
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| 41. |
- Örestig, Johan, 1979-
(författare)
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The long and winding road : A life course approach to retirement behaviour
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Background: This thesis explores the retirement behaviour of older people approaching retirement decisions. The research questions in focus deal with the attitudes toward work, the retirement preferences and the subjective well-being of the "youngest old", i.e. people aged 55–64. The included studies analyse the social determinants of these subjective evaluations and how they predict the timing of retirement and post-retirement well-being.Methods: In the included studies, methods are used that allow us to follow developments over time. Repeated cross-sectional analyses are employed to examine general developments pertaining to the older work force. These include OLS and logistic regression analysis. Longitudinal analyses are used to follow individual developments over time. These include Structural equation modelling and Cox regression analysis.Results: The results indicate that subjective evaluations such as attitudes to work and retirement preferences, as well as subjective well-being, are closely related to the structural conditions to which individuals are exposed, i.e. class position and work environment. The results also indicate that subjective evaluations such as preferred exit age and subjective well-being reported while in the work force are determinants of both the timing of retirement (in the case of preferred exit age and pre-retirement subjective well-being) and post-retirement subjective well-being (in the case of pre-retirement subjective well-being).Also, results indicate that recent policy changes in the Swedish pension systems are reflected in the retirement preferences of the older work force. A comparison of two time-points representing the incentive structure of the old and the new pension systems indicates that preferences were delayed with pension reform.Conclusion: The thesis contributes a temporal perspective to a research field that is dominated by research studying retirement behaviour at a single point of in time. The included studies underline the value of understanding retirement behaviour as a process rather than an isolated event. The way people evaluate their work, their well-being and their retirement prospects is intimately intertwined with their earlier experience. These subjective evaluations affect future retirement outcomes. Life course approaches offer illuminating tools for examining and explaining the significance of the biographies behind retirement behaviour.
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