Pub Date : 2017-10-25DOI: 10.4249/scholarpedia.33321
A. Barrau
The loop quantum gravity theory is a background-independent and non-perturbative quantization of general relativity. It has been developed both in the canonical and covariant formalisms. As for all tentative theories of quantum gravity, one of the key question is to produce clear experimental or observational predictions. As the discrete nature of spacetime at the Planck scale is extremely difficult to probe directly, phenomenological attempts do focus mostly on the cosmological sector, on black holes and on possible high energy astrophysics effects. The main prediction of loop quantum gravity in the cosmological sector is that the Big Bang is replaced by a Big Bounce: a contracting phase should have taken place before the expanding phase we are now living in. In the black hole sector, the Hawking evaporation spectrum should receive substantial corrections and the very existence of an event horizon can be questioned, potentially leading to black holes bouncing into white holes. Finally, on the astroparticle physics side, the quantum discreteness of spacetime could lead to interesting effects for high energy cosmic rays.
{"title":"Astrophysical and cosmological signatures of Loop Quantum Gravity","authors":"A. Barrau","doi":"10.4249/scholarpedia.33321","DOIUrl":"https://doi.org/10.4249/scholarpedia.33321","url":null,"abstract":"The loop quantum gravity theory is a background-independent and non-perturbative quantization of general relativity. It has been developed both in the canonical and covariant formalisms. As for all tentative theories of quantum gravity, one of the key question is to produce clear experimental or observational predictions. As the discrete nature of spacetime at the Planck scale is extremely difficult to probe directly, phenomenological attempts do focus mostly on the cosmological sector, on black holes and on possible high energy astrophysics effects. The main prediction of loop quantum gravity in the cosmological sector is that the Big Bang is replaced by a Big Bounce: a contracting phase should have taken place before the expanding phase we are now living in. In the black hole sector, the Hawking evaporation spectrum should receive substantial corrections and the very existence of an event horizon can be questioned, potentially leading to black holes bouncing into white holes. Finally, on the astroparticle physics side, the quantum discreteness of spacetime could lead to interesting effects for high energy cosmic rays.","PeriodicalId":74760,"journal":{"name":"Scholarpedia journal","volume":"12 1","pages":"33321"},"PeriodicalIF":0.0,"publicationDate":"2017-10-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45345918","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2017-08-30DOI: 10.4249/scholarpedia.33311
T. Heida, J. Modolo
{"title":"Models of deep brain stimulation","authors":"T. Heida, J. Modolo","doi":"10.4249/scholarpedia.33311","DOIUrl":"https://doi.org/10.4249/scholarpedia.33311","url":null,"abstract":"","PeriodicalId":74760,"journal":{"name":"Scholarpedia journal","volume":"12 1","pages":"33311"},"PeriodicalIF":0.0,"publicationDate":"2017-08-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47954972","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2017-06-06DOI: 10.4249/scholarpedia.32997
J. Donoghue
An Effective Field Theory is one which uses only the active degrees of freedom available at some energy. A full quantum field theory treatment is applied. When done properly, the results encode the quantum corrections appropriate to that energy. The perturbative treatment of quantum General Relativity behaves as an effective field theory, and well defined quantum corrections can be calculated. This review discusses effective field theory and its application to general relativity.
{"title":"Quantum gravity as a low energy effective field theory","authors":"J. Donoghue","doi":"10.4249/scholarpedia.32997","DOIUrl":"https://doi.org/10.4249/scholarpedia.32997","url":null,"abstract":"An Effective Field Theory is one which uses only the active degrees of freedom available at some energy. A full quantum field theory treatment is applied. When done properly, the results encode the quantum corrections appropriate to that energy. The perturbative treatment of quantum General Relativity behaves as an effective field theory, and well defined quantum corrections can be calculated. This review discusses effective field theory and its application to general relativity.","PeriodicalId":74760,"journal":{"name":"Scholarpedia journal","volume":"12 1","pages":"32997"},"PeriodicalIF":0.0,"publicationDate":"2017-06-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46233876","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2017-04-16DOI: 10.4249/scholarpedia.42285
J. Brooks, Jared Medina
{"title":"Perceived location of touch","authors":"J. Brooks, Jared Medina","doi":"10.4249/scholarpedia.42285","DOIUrl":"https://doi.org/10.4249/scholarpedia.42285","url":null,"abstract":"","PeriodicalId":74760,"journal":{"name":"Scholarpedia journal","volume":"12 1","pages":"42285"},"PeriodicalIF":0.0,"publicationDate":"2017-04-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44802036","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2017-03-30DOI: 10.4249/scholarpedia.42449
V. Ntziachristos, Andreas Buehler
To the Editor: In chronic inflammatory diseases, uncontrolled inflammation is associated with increased rates of hospitalization, complications, and death. Because of the potential severity of these conditions, there is an increased demand for new diagnostic approaches.1,2 Multispectral optoacoustic tomography (MSOT) is a new imaging technique that permits the noninvasive quantification of hemoglobin-dependent tissue perfusion and oxygenation as surrogates of inflammation.3 This approach uses the excitation of short-pulsed laser light with near-infrared wavelengths to induce the photoacoustic effect in targeted tissues, which results in detectable sound waves induced by thermoelastic expansion. In this single-center, cross-sectional diagnostic study (ClinicalTrials.gov number, NCT02622139), MSOT Acuity Echo (iThera Medical) was used to perform transabdominal evaluation of intestinal inflammation in 108 patients with Crohn’s disFigure 1 (facing page). MSOT Imaging for the Assessment of Crohn’s Disease Activity. Panel A shows the transabdominal imaging approach, which uses the same detector for laser light emission and ultrasonic detection of signal levels by means of multispectral optoacoustic tomography (MSOT). Erythrocytes are the target for laser-light absorption and ultrasonic emission. Six different wavelengths (700, 730, 760, 800, 850, and 900 nm) were used for MSOT data acquisition; MSOT measurements, such as total hemoglobin (Hb), oxygenated Hb, deoxygenated Hb, and oxygen saturation, are calculated from these measurements. These hemoglobin-based measurements permit the evaluation of tissue perfusion and oxygenation as surrogates of inflammation with MSOT. Panel B shows MSOT-derived total Hb signal levels in the intestinal wall (in both the large bowel and the small intestine) in 44 patients with Crohn’s disease with different degrees of endoscopic inflammation. Such evaluation was performed by means of the Simplified Endoscopic Score for Crohn’s Disease (SES-CD), which ranges from 0 to 56, with higher scores indicating a greater severity of intestinal inflammation; remission is defined as a score of less than 3, low disease activity as a score of 3 to 6, moderate disease activity as a score of 7 to 15, and high disease activity as a score of 16 or more. The signal levels are expressed as normalized z scores and transformed into a linear scale of arbitrary units (au). The red dots represent single measurements for each patient; the horizontal lines indicate medians, and I bars the interquartile range. A single asterisk denotes P<0.05 and a double asterisk P<0.001 for the comparison with remission. Panel C shows representative images of MSOT measurements of total Hb in the large bowel and small intestine in patients with different grades of endoscopic disease activity (as evaluated by means of SES-CD). The top row shows representative MSOT measurements of total Hb as color-coded maps with an overlay of B-mode ultrasonographic images. The mi
{"title":"Multispectral optoacoustic tomography","authors":"V. Ntziachristos, Andreas Buehler","doi":"10.4249/scholarpedia.42449","DOIUrl":"https://doi.org/10.4249/scholarpedia.42449","url":null,"abstract":"To the Editor: In chronic inflammatory diseases, uncontrolled inflammation is associated with increased rates of hospitalization, complications, and death. Because of the potential severity of these conditions, there is an increased demand for new diagnostic approaches.1,2 Multispectral optoacoustic tomography (MSOT) is a new imaging technique that permits the noninvasive quantification of hemoglobin-dependent tissue perfusion and oxygenation as surrogates of inflammation.3 This approach uses the excitation of short-pulsed laser light with near-infrared wavelengths to induce the photoacoustic effect in targeted tissues, which results in detectable sound waves induced by thermoelastic expansion. In this single-center, cross-sectional diagnostic study (ClinicalTrials.gov number, NCT02622139), MSOT Acuity Echo (iThera Medical) was used to perform transabdominal evaluation of intestinal inflammation in 108 patients with Crohn’s disFigure 1 (facing page). MSOT Imaging for the Assessment of Crohn’s Disease Activity. Panel A shows the transabdominal imaging approach, which uses the same detector for laser light emission and ultrasonic detection of signal levels by means of multispectral optoacoustic tomography (MSOT). Erythrocytes are the target for laser-light absorption and ultrasonic emission. Six different wavelengths (700, 730, 760, 800, 850, and 900 nm) were used for MSOT data acquisition; MSOT measurements, such as total hemoglobin (Hb), oxygenated Hb, deoxygenated Hb, and oxygen saturation, are calculated from these measurements. These hemoglobin-based measurements permit the evaluation of tissue perfusion and oxygenation as surrogates of inflammation with MSOT. Panel B shows MSOT-derived total Hb signal levels in the intestinal wall (in both the large bowel and the small intestine) in 44 patients with Crohn’s disease with different degrees of endoscopic inflammation. Such evaluation was performed by means of the Simplified Endoscopic Score for Crohn’s Disease (SES-CD), which ranges from 0 to 56, with higher scores indicating a greater severity of intestinal inflammation; remission is defined as a score of less than 3, low disease activity as a score of 3 to 6, moderate disease activity as a score of 7 to 15, and high disease activity as a score of 16 or more. The signal levels are expressed as normalized z scores and transformed into a linear scale of arbitrary units (au). The red dots represent single measurements for each patient; the horizontal lines indicate medians, and I bars the interquartile range. A single asterisk denotes P<0.05 and a double asterisk P<0.001 for the comparison with remission. Panel C shows representative images of MSOT measurements of total Hb in the large bowel and small intestine in patients with different grades of endoscopic disease activity (as evaluated by means of SES-CD). The top row shows representative MSOT measurements of total Hb as color-coded maps with an overlay of B-mode ultrasonographic images. The mi","PeriodicalId":74760,"journal":{"name":"Scholarpedia journal","volume":"12 1","pages":"42449"},"PeriodicalIF":0.0,"publicationDate":"2017-03-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41627642","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2017-02-15DOI: 10.4249/scholarpedia.42361
A. Maye, Carme Isern-Mas, Pamela Barone, J. Michael
Joint attention is a social-cognitive phenomenon in which two or more agents direct their attention together towards the same object. Definitions range from this rather broad conception to more specific definitions which require that, in addition, attention be directed to the same aspect of that object and that agents need to be mutually aware of their jointly attending. Joint attention is an important coordination mechanism in joint action. The capacity for engaging in joint attention, in particular in the sense of this narrower definition, is frequently taken to indicate the presence of theory of mind in the participating agents, and is also implicated in the development of theory of mind. However, the prominence of sensorimotor components in establishing and sustaining episodes of joint attention — e.g., eye and head movements, pointing and vocalizations — suggests that sensorimotor approaches to social interaction may be well-placed to account for important parts of joint attention without invoking theory-of-mind abilities, and may therefore provide a valuable alternative to approaches emphasizing theory of mind. In particular, sensorimotor accounts may explain aspects of joint attention through the dynamics and regularities in the sensorimotor processes that coordinate the activities of the agents.
{"title":"Sensorimotor accounts of joint attention","authors":"A. Maye, Carme Isern-Mas, Pamela Barone, J. Michael","doi":"10.4249/scholarpedia.42361","DOIUrl":"https://doi.org/10.4249/scholarpedia.42361","url":null,"abstract":"Joint attention is a social-cognitive phenomenon in which two or more agents direct their attention together towards the same object. Definitions range from this rather broad conception to more specific definitions which require that, in addition, attention be directed to the same aspect of that object and that agents need to be mutually aware of their jointly attending. Joint attention is an important coordination mechanism in joint action. The capacity for engaging in joint attention, in particular in the sense of this narrower definition, is frequently taken to indicate the presence of theory of mind in the participating agents, and is also implicated in the development of theory of mind. However, the prominence of sensorimotor components in establishing and sustaining episodes of joint attention — e.g., eye and head movements, pointing and vocalizations — suggests that sensorimotor approaches to social interaction may be well-placed to account for important parts of joint attention without invoking theory-of-mind abilities, and may therefore provide a valuable alternative to approaches emphasizing theory of mind. In particular, sensorimotor accounts may explain aspects of joint attention through the dynamics and regularities in the sensorimotor processes that coordinate the activities of the agents.","PeriodicalId":74760,"journal":{"name":"Scholarpedia journal","volume":"12 1","pages":"42361"},"PeriodicalIF":0.0,"publicationDate":"2017-02-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47347436","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2017-01-01DOI: 10.4249/scholarpedia.32372
S. Ebara, T. Furuta, K. Kumamoto
{"title":"Vibrissal mechanoreceptors","authors":"S. Ebara, T. Furuta, K. Kumamoto","doi":"10.4249/scholarpedia.32372","DOIUrl":"https://doi.org/10.4249/scholarpedia.32372","url":null,"abstract":"","PeriodicalId":74760,"journal":{"name":"Scholarpedia journal","volume":"12 1","pages":"32372"},"PeriodicalIF":0.0,"publicationDate":"2017-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"70978839","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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