867 research outputs found
An operationalization of Stevenson’s conceptualization of entrepreneurship as opportunity-based firm behavior
No full textThis is the author-version of article published as: Brown, Terrence and Davidsson, Per and Wiklund, Johan (2001) An operationalization of Stevenson’s conceptualization of entrepreneurship as opportunity-based firm behavior. Strategi
Regeneration of Peripheral Nerves. The role of protein kinases, with emphasis on neurotrophic factor stimulation
No full textThe purpose of this study was to investigate the role of protein kinases in peripheral nerve regeneration, with the use of dorsal root ganglia (DRG) and nodose ganglia explants from adult mice. The effects of neurotrophic factor stimulation and protein kinase inhibition were studied for long (days) and short term (minutes) effects. The protein kinase systems studied were protein kinase C (PKC), the cyclic nucleotide dependent protein kinases A and G (PKA, PKG) and the mitogen activated protein kinase (MAPK). When unstimulated regeneration was concerned, inhibition of either PKC or PKA and PKG showed minor or transient effects on both long- and short term axonal outgrowth. Simultaneous inhibition of PKC and PKA/PKG on both unstimulated and NGF stimulated DRG had much stronger effects, suggesting that complementary kinase systems work together during outgrowth. Inhibition of MAPK also lacked effects on unstimulated DRG or nodose ganglia. When neurotrophic factors were used on DRG, MAPK inhibition effectively inhibited both NGF and glial cell line-derived (GDNF) stimulated outgrowth. In contrast to this, neurotrophin-3 (NT-3) stimulated DRG outgrowth was further increased after inhibition of MAPK. Neurotrophin-4 (NT-4) activated MAPK and strongly stimulated axonal outgrowth from the nodose ganglion; yet MAPK inhibition was without effect on the NT-4 stimulated nodose outgrowth. The results thus show that the relative importance of MAPK varies between unstimulated and different types of stimulated growth in peripheral neurons, perhaps in a neuronal population specific way
Conceptual and Empirical Challenges in the Study of Firm Growth
No full textWhen the first author reviewed the literature on small firm growth in the mid 1980’s for his disserta-tion work, he noted that surprisingly few studies had focused on that specific problem (Davidsson 1989a; 1989b). Today, this is no longer true. In recent years ever more comprehensive lists of studies have been compiled and reviewed. Storey (1994) compiled results from more than 25 studies. Delmar (1997) scrutinized the operationalizations of growth in 55 studies. The second author of the present manuscript recently reviewed and classified close to 70 studies for his dissertation work (Wiklund, 1998), while Ardishvili, Cardozo, Harmon & Vadakath (1998) included in their classification a full 105 published and unpublished studies focusing on new and/or small firm growth. \ud
However, rather than presenting a set of solid generalizations on the causes and effects of growth, these reviewers all tend to come up with relatively critical accounts. These criticisms concern both theoretical and methodological shortcomings. (Storey, 1994, p. 5; 125, Cooper, 1995, p. 120; Delmar (1997, pp. 205; 212; Wiklund, 1998, pp. 6-7; 19; Ardishvili et al, 1998, p. 1) \ud
In addition to the above evaluations of research specifically on growth, we also have the observation that longitudinal designs are generally lacking in entrepreneurship research (Cooper 1995, p. 112; Wik-lund 1998, p. 7). In the latest ‘State-of-the-Art’ volume, several authors mentioned the lack of longitu-dinal studies in entrepreneurship research as a major impediment (Aldrich & Baker, 1997, p. 389; Sex-ton, 1997, p. 407) \ud
As a result of the shortcomings pointed out by the critics, it is still true today that knowledge about what facilitates and hinders growth is still scattered and limited. The same is true for insights into the process of firm growth. Apparently, the large number of empirical studies has not given a very high yield of generalizable knowledge. This suggests that researchers who set out to contribute meaningfully to this line of empirical research have a number of challenges to deal with. On the basis of the criticism summarized above we would suggest that some of the more important challenges are the following:\ud
• to develop a satisfactory basic research design\ud
• to apply a well-founded conceptualization of growth, which in turn requires a well thought-out con-ceptualization of ‘the firm’\ud
• to adequately match this conceptualization with the purpose of the study, the theories used, and the operationalization of growth.\ud
\ud
In the remainder of this chapter we will elaborate our views on these challenges. In the next section we will argue that growth studies need to be longitudinal, and why this is so. We will then turn to the conceptualization of the firm and the unit of analysis in growth studies, which turns out to be a really difficult problem. After that we discuss theoretical perspectives and how these match with different conceptualizations of the firm. Finally, we turn to operationalization issues, i.e. the choice of growth indicators, specific ways to model growth trajectories, and the distinction between organic and acquired growth. Throughout, we also discuss how these issues relate to different purposes, i.e. whose knowl-edge interests the study aims to satisfy
Regeneration of Peripheral Nerves. The role of protein kinases, with emphasis on neurotrophic factor stimulation
No full textPopular Abstract in Swedish Regeneration av perifera nerver. Proteinkinasers betydelse, speciellt med avseende på ämnen som stimulerar nervtillväxt. Perifera nerver är belägna utanför hjärnan eller ryggmärgen. De har kontakt med och styr organ i kroppen. Med regeneration av nerver menas återutväxten av nervecllens utlöpare, axonet, och återetablering av kontakten med målorganet. Substanser som stimulerar nervtillväxt kallas neurotrofiska faktorer. Proteinkinaser är proteiner som aktiverar andra proteiner genom att sätta på en eller flera fosfatgrupper. Syftet med studien var att undersöka proteinkinasers roll i perifer nervregeneration. En samling av nervcellkroppar kallas för ett ganglion. De perifera nervpreparaten som användes i studien var dorsalrotsganglier (DRG, lumbal 4 och 5) och ganglion nodosum (GN) från vuxna möss. Dorsalrotsganglierna är belägna strax utanför ryggmärgen, ungefär i midjehöjd och förmedlar sinnesintryck från ischiasnerven. Man har två ganglion nodosum, ett på vardera sidan av struphuvudet, och de är inblandade i bl. a. kontrollen av hjärta och lungor. Följderna av stimulering med neurotrofiska faktorer och hämning av proteinkinaser undersöktes med avseende på långtids (dagar) och korttids (minuter) effekter. Hämning av enskilda proteinkinaser på ostimulerad utväxt gav små eller övergående effekter. Samtidig hämning av tre proteinkinaser, på både ostimulerad och utväxt stimulerad med den neurotrofiska faktorn (NGF), gav mycket starkare effekter, vilket antyder att vissa proteinkinaser samarbetar under regenerationen. Djupare studium av ett proteinkinas, mitogenaktiverat proteinkinas (MAPK), i både DRG och GN visade att ett och samma proteinkinas kan ha olika roller i ostimulerad och stimulerad axonal utväxt i perifera neuron, kanske beroende på de i ganglierna ingående olika nervcellstyperna. För en mer detaljerad redovisning av de enskilda proteinkinassystemen och resultaten, se nedan. De studerade proteinkinaserna var proteinkinas C (PKC), de cykliskt adenosinmonofosfat- (cAMP-) och cykliskt guanidinmonofosfat- (cGMP) beroende proteinkinaserna A och G (PKA och PKG) samt det mitogenaktiverade proteinkinaset (MAPK). Hämning av antingen PKC eller PKA och PKG gav små eller övergående effekter på ostimulerad axonal utväxt. Samtidig hämning av både PKC och PKA/PKG, på både ostimulerade och DRG stimulerade med nervtillväxtfaktor (NGF), gav mycket starkare effekter, vilket antyder att vissa proteinkinaser samarbetar under regenerationen.Hämning av MAPK saknade också effekter på ostimulerade DRG eller GN. I samband med neurotrofisk stimulering av DRG visade sig en hämning av MAPK effektivt reducera både NGF och glia cellinje-härledd neurotrofisk faktor (GDNF) stimulerad utväxt. I tydlig kontrast mot detta stimulerades neurotrofin-3 (NT-3) stimulerad utväxt ytterligare efter hämning av MAPK. Neurotrofin-4 (NT-4) stimulerade axonal utväxt från GN kraftigt och aktiverade MAPK. Trots detta hade MAPK hämning av NT-4 stimulerad GN-utväxt ingen effekt. Resultaten visar därmed att MAPKs betydelse varierar mellan ostimulerad och olika typer av stimulerad utväxt i perifera neuron, möjligen beroende av de i ganglierna ingående olika nervcellstyperna.The purpose of this study was to investigate the role of protein kinases in peripheral nerve regeneration, with the use of dorsal root ganglia (DRG) and nodose ganglia explants from adult mice. The effects of neurotrophic factor stimulation and protein kinase inhibition were studied for long (days) and short term (minutes) effects. The protein kinase systems studied were protein kinase C (PKC), the cyclic nucleotide dependent protein kinases A and G (PKA, PKG) and the mitogen activated protein kinase (MAPK). When unstimulated regeneration was concerned, inhibition of either PKC or PKA and PKG showed minor or transient effects on both long- and short term axonal outgrowth. Simultaneous inhibition of PKC and PKA/PKG on both unstimulated and NGF stimulated DRG had much stronger effects, suggesting that complementary kinase systems work together during outgrowth. Inhibition of MAPK also lacked effects on unstimulated DRG or nodose ganglia. When neurotrophic factors were used on DRG, MAPK inhibition effectively inhibited both NGF and glial cell line-derived (GDNF) stimulated outgrowth. In contrast to this, neurotrophin-3 (NT-3) stimulated DRG outgrowth was further increased after inhibition of MAPK. Neurotrophin-4 (NT-4) activated MAPK and strongly stimulated axonal outgrowth from the nodose ganglion; yet MAPK inhibition was without effect on the NT-4 stimulated nodose outgrowth. The results thus show that the relative importance of MAPK varies between unstimulated and different types of stimulated growth in peripheral neurons, perhaps in a neuronal population specific way
Technical Advances in Robotic Renal Surgery
No full textSurgical techniques for robotic renal surgery are driven by the aims of simplifying the most challenging surgical steps, maximizing functional and oncologic outcomes, and consistently pushing the envelope on possibilities. Over the past several years, not only we have seen an emergence in innovation in surgical technique and robotic platforms, we also note an integration of a variety of imaging techniques. Thanks to advances in imaging technology and surgical methods, surgeons can now contemplate partial nephrectomy in patients who were previously thought to be impossible candidates for nephron-sparing surgery. Recent studies have concentrated on integrating the architecture of renal masses and their vasculature to improve surgical planning, combining imaging and hilar clamping techniques and introducing a single-port robotic platform. The innovations introduced in the field of robotic renal surgery have shown substantial improvements in preoperative planning and intraoperative guidance. Moreover, new surgical platforms have recently appeared on the market showing encouraging results. With developing robotic expertise and new implementations, it is plausible that practicing urologists will continue to push the boundaries in nephron preservation and complication-free recovery
Development of a method to measure regional perfusion of the lung in anesthetized ponies using computed tomography angiography and the maximum slope model
No full textOBJECTIVETo develop a method based on CT angiography and the maximum slope model (MSM) to measure regional lung perfusion in anesthetized ponies.ANIMALS6 ponies.PROCEDURESAnesthetized ponies were positioned in dorsal recumbency in the CT gantry. Contrast was injected, and the lungs were imaged while ponies were breathing spontaneously and while they were mechanically ventilated. Two observers delineated regions of interest in aerated and atelectatic lung, and perfusion in those regions was calculated with the MSM. Measurements obtained with a computerized method were compared with manual measurements, and computerized measurements were compared with previously reported measurements obtained with microspheres.RESULTSPerfusion measurements obtained with the MSM were similar to previously reported values obtained with the microsphere method. While ponies were spontaneously breathing, mean +/- SD perfusion for aerated and atelectatic lung regions were 4.0 +/- 1.9 and 5.0 +/- 1.2 mL/min/g of lung tissue, respectively. During mechanical ventilation, values were 4.6 +/- 1.2 and 2.7 +/- 0.7 mL/min/g of lung tissue at end expiration and 4.1 +/- 0.5 and 2.7 +/- 0.6 mL/min/g of lung tissue at peak inspiration. Intraobserver agreement was acceptable, but interobserver agreement was lower. Computerized measurements compared well with manual measurements
Development and validation of 3D printed virtual models for robot-assisted radical prostatectomy and partial nephrectomy: urologistsâ and patientsâ perception
No full textPurpose: To test the face and content validity of 3D virtual-rendered printed models used before robot-assisted prostate cancer and nephron-sparing surgery. Methods: Patients who underwent live surgery during an international urological meeting organized in January 2017 were enrolled. Those with organ-confined prostate cancer underwent robot-assisted radical prostatectomy. Patients with a single renal tumor underwent minimally invasive nephron-sparing surgery. High-resolution (HR) imaging was obtained for all patients. Those with kidney tumors received contrast-enhanced CT scan with angiography; those with prostate cancer underwent mp-MRI. Images in DICOM format were processed by dedicated software. The first step was the rendering of a 3D virtual model. The models were then printed. They were presented during the live surgery of the urological meeting. All the participants and the operated patients were asked to fill a questionnaire about their opinion expressed in Likert scale (1â10) about the use and application of the 3D printed models. Results: 18 patients were enrolled, including 8 undergoing robot-assisted radical prostatectomy and 10 undergoing minimally invasive partial nephrectomy. For each patient, a virtual 3D printed model was created. The attendants rated the utility of printed models in surgical planning, anatomical representation and the role of technology in surgical training as 8/10, 10/10 and 9/10, respectively. All patients reported favorable feedbacks (from 9 to 10/10) about the use of the technology during the case discussion with the surgeon. Conclusions: In our experience, 3D printing technology has been perceived as a useful tool for the purpose of surgical planning, physician education/training and patient counseling. Further researches are expected to increase the level of evidence
Robot-Assisted Adrenalectomy Workup and Management
No full textRobot-assisted approach for adrenalectomy is feasible and safe. Although adrenalectomy is a purely extirpative procedure requiring no further reconstruction, wristed instruments, increased precision, and magnified three-dimensional vision may aid in dissection of large and small vessels and more precise delineation of the tumor lesion during both radical and partial adrenalectomies. These advantages may allow more surgeons, including those with limited laparoscopic experience, to offer their patients an effective and minimally invasive approach to adrenalectomy
Magnetic resonance imaging in prostate cancer detection and management : a systematic review
No full textINTRODUCTION: The aim of our work was to evaluate the role of multi-parametric magnetic resonance imaging (mp-MRI) in detection and management of prostate cancer (PC); specifically investigating the efficacy of mpMRI-based biopsy techniques in terms of diagnostic yield of significant prostate neoplasm and the improved management of patients who choose conservative treatments or active surveillance. EVIDENCE ACQUISITION: A systematic and critical analysis through Medline, Embase, Scopus and Web of Science databases was carried out in March 2016, following the PRISMA ("Preferred Reporting Items for Systematic Reviews and Meta-Analyses") statement. The search was conducted using the following key words: "MRI/TRUS-fusion biopsy," "PIRADS," "prostate cancer," "magnetic resonance imaging (MRI)," "multiparametric MRI (mpMRI)," "systematic prostate biopsy (SB)," "targeted prostate biopsy (TPB)." English language articles were reviewed for inclusion ability. EVIDENCE SYNTHESIS: Sixty-six studies were selected in order to evaluate the characteristics and limitations of traditional sample biopsy, the role of mpMRI in detection of PC, specifically the increased degree of diagnostic accuracy of targeted prostate biopsy compared to systematic biopsy (12 cores), and to transperineal saturation biopsies with trans-rectal ultrasound (TRUS) only. MpMRI can detect index lesions in approximately 90% of cases when compared to prostatectomy specimen. The diagnostic performance of biparametric MRI (T2w + DWI) is not inferior to mpMRI, offering valid options to diminish cost- and time-consumption. Since approximately 10% of significant lesions are still MRIinvisible, systematic cores biopsy seem to still be necessary. The analysis of the different techniques shows that in-bore MRI-guided biopsy and MRI/TRUS-fusion-guided biopsy are superior in detection of significant PC compared to visual estimation alone. MpMRI proved to be very effective in active surveillance, as it prevents underdetection of significant PC and it assesses low-risk disease accurately. In higher-risk disease, presurgical MRI may change the clinically-based surgical plan in up to a third of cases. CONCLUSIONS: Targeted prostate biopsy, guided by mpMRI, is able to improve diagnostic accuracy and to reduce the detection of insignificant PC. Since the negative predictive value (NPV) of mpMRI is still imperfect, systematic cores biopsy should not be omitted for optimal staging of disease. A process of a progressive and periodic evolution in the detection and radiological classification of prostate lesions (such as PIRADS), is still needed in patients in active surveillance and in radical prostatectomy planning
Apples and oranges: comparison of treatment methods for prostate cancer using biochemical recurrence as an endpoint.
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