Lateral interactions in visual perception of temporal signals: cortical and subcortical components

The aim of this work was to isolate and investigate subcortical and cortical lateral interactions involved in flicker perception. We quantified the perceived flicker strength (PFS) in the center of a test stimulus which was simultaneously modulated with a surround stimulus (50% Michelson contrast in both stimuli). Subjects were requested to adjust the modulation depth of a separate matching stimulus that was physically identical to the center of the test stimulus but without the surround. Using LCD goggles, synchronized to the frame rate of a CRT screen, the center and surround could be presented monoptically or dichoptically. In the monoptic condition, center-surround interactions can have both subcortical and cortical origins. In the dichoptic condition, center-surround interactions cannot occur in the retina and the LGN, therefore isolating a cortical mechanism. Results revealed both a strong monoptic (subcortical plus cortical) lateral interaction and a weaker dichoptic (cortical) lateral interaction. Subtraction of the dichoptic from the monoptic data revealed a subcortical mechanism of the lateral interaction. While the modulation of the cortical PFS component showed a low-pass temporal-frequency tuning, the modulation of the subcortical PFS component was maximal at 6 Hz. These findings are consistent with two separate temporal channels influencing the monoptic PFS, each with distinct lateral interactions strength and frequency tuning characteristics. We conclude that both subcortical and cortical lateral interactions modulate flicker perception.

Avaliação da retinopatia hipertensiva através do potencial oscilatório do eletrorretinograma

OBJETIVO: Avaliar o comportamento do potencial oscilatório escotópico do eletrorretinograma de campo total (ERG) na retinopatia hipertensiva. MÉTODOS: Quarenta e quatro pacientes foram submetidos à avaliação clínica e subdivididos em dois grupos: 26 hipertensos (HT) com média de idade de 52,23 ± 5,79 anos divididos em 10 homens (38,46%) e 16 mulheres (61,54%) e 18 normotensos (NT) com média de idade de 51,79 ± 10,23 anos divididos em 5 homens (27,78%) e 13 mulheres (72,22%). Foram incluídos no estudo apenas hipertensos leves a moderados (estágio 1 e 2 respectivamente) sem lesões em outro órgão-alvo.Os pacientes hipertensos foram mantidos sob placebo durante o período do estudo. Em seguida, foram submetidos à avaliação oftalmológica e realização do ERG. O eletrorretinograma de campo total (ERG), com registro das respostas: escotópica, escotópica máxima, PO escotópico, fotópica e "flicker". Para análise da resposta do PO foi considerada a latência dos dois primeiros picos e o valor médio da amplitude dos três picos do complexo de três respostas consecutivas, denominado índice oscilatório (IO). RESULTADOS: A hipertensão arterial acometia 26 (59,1%) dos pacientes, ao passo que 18 (40,9%) eram normotensos. A média do IO obtido foi de 257,41µV no grupo de NT e de 217,81 µV no HT (p=0,006). As médias de latências obtidas para os picos 1 (NT-18,42 ms e HT-17,91 ms) e 2 (NT-24,54 ms e HT- 24,29 ms) não foram diferentes entre os grupos (p>0,05). CONCLUSÃO: Os hipertensos apresentam índice oscilatório significativamente menor que os normotensos, sugerindo que a hipertensão arterial pode ocasionar disfunção da retina interna.

Investigation of Bulk and DTMOS triple-gate devices under 60 MeV proton irradiation

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Laser locking to the Hg-199 S-1(0)-P-3(0) clock transition with 5.4x10(-15)/root tau fractional frequency instability

With Hg-199 atoms confined in an optical lattice trap in the Lamb-Dicke regime, we obtain a spectral line at 265.6 nm for which the FWHM is similar to 15 Hz. Here we lock an ultrastable laser to this ultranarrow S-1(0) - P-3(0) clock transition and achieve a fractional frequency instability of 5.4 x 10(-15) / root tau for tau <= 400 s. The highly stable laser light used for the atom probing is derived from a 1062.6 nm fiber laser locked to an ultrastable optical cavity that exhibits a mean drift rate of -6.0 x 10(-17) s-(1) (-16.9 mHzs(-1) at 282 THz) over a six month period. A comparison between two such lasers locked to independent optical cavities shows a flicker noise limited fractional frequency instability of 4 x 10(-16) per cavity. (c) 2012 Optical Society of America

Electroretinographic findings associated with panretinal photocoagulation (PRP) versus PRP plus intravitreal ranibizumab treatment for high-risk proliferative diabetic retinopathy

To evaluate changes in electroretinographic (ERG) findings after panretinal photocoagulation (PRP) compared to PRP plus intravitreal injection of ranibizumab (IVR) in eyes with high-risk proliferative diabetic retinopathy (PDR). Patients with high-risk PDR and no prior laser treatment were assigned randomly to receive PRP (PRP group; n = 9) or PRP plus IVR (PRPplus group; n = 11). PRP was administered in two sessions (weeks 0 and 2), and IVR was administered at the end of the first laser session (week 0) in the PRPplus group. Standardized ophthalmic evaluations including (ETDRS) best-corrected visual acuity (BCVA), and fluorescein angiography to measure area of fluorescein leakage (FLA), were performed at baseline and at weeks 16 (+/- 2), 32 (+/- 2) and 48 (+/- 2). ERG was measured according to ISCEV standards at baseline and at week 48 (+/- 2). At 48 weeks, 2,400-3,000 laser spots had been placed in eyes in the PRP group, while only 1,400-1,800 spots had been placed in the PRPplus group. Compared to baseline, there was a statistically significant (P < 0.05) FLA reduction observed at all study visits in both groups, with the reduction observed in the PRPplus group significantly larger than that in the PRP group at week 48. ROD b-wave amplitude was significantly reduced to 46 +/- A 5 % (P < 0.05) of baseline in the PRP group and 64 +/- A 6 % (P < 0.05) in the PRPplus group. This reduction was significantly larger in the PRP group than in the PRPplus group (P = 0.024; t Test). Similar results were observed for the dark-adapted Combined Response (CR) b-wave amplitude, with a reduction at 48 weeks compared to baseline of 45 +/- A 4 % in the PRP group and 62 +/- A 5 % in the PRPplus group; the reduction in CR b-wave amplitude was significantly larger in the PRP group than in the PRPplus group (P = 0.0094). CR a-wave, oscillatory potentials, cone single flash, and 30 Hz flicker responses showed statistically significant within-group reductions, but no differences in between-group analyses. These results suggest that treating high-risk PDR with PRP plus IVR is effective for PDR control, and permits the use of less extensive PRP which, in turn, induces less retinal functional loss, in particular for rod-driven post-receptoral responses, than treatment with PRP alone.

Characterization and modeling of low-frequency noise in MOSFETs

For many years, RF and analog integrated circuits have been mainly developed using bipolar and compound semiconductor technologies due to their better performance. In the last years, the advance made in CMOS technology allowed analog and RF circuits to be built with such a technology, but the use of CMOS technology in RF application instead of bipolar technology has brought more issues in terms of noise. The noise cannot be completely eliminated and will therefore ultimately limit the accuracy of measurements and set a lower limit on how small signals can be detected and processed in an electronic circuit. One kind of noise which affects MOS transistors much more than bipolar ones is the low-frequency noise. In MOSFETs, low-frequency noise is mainly of two kinds: flicker or 1/f noise and random telegraph signal noise (RTS). The objective of this thesis is to characterize and to model the low-frequency noise by studying RTS and flicker noise under both constant and switched bias conditions. The effect of different biasing schemes on both RTS and flicker noise in time and frequency domain has been investigated.

Untersuchung zum Beitrag des ON-Kanals zu zeitlichen und chromatischen Verarbeitungsmechanismen in der Retina

Ziel der vorliegenden Arbeit war es, mithilfe von Dressurexperimenten in Kombination mit dem Einsatz von Neuropharmaka die Bedeutung des retinalen ON-Kanals für zwei visuelle Leistungen des Goldfisches – das kontrastabhängige zeitliche Auflösungsvermögen sowie die Wellenlängenunterscheidungsfähigkeit - zu untersuchen. Da die Tiere nach der pharmakologischen Blockade keinerlei verändertes Verhalten zeigten, kann davon ausgegangen werden, dass der retinale ON-Kanal weder für die Prozessierung des kontrastabhängigen zeitlichen Auflösungsvermögens noch für die Wellenlängenunterscheidungsfähigkeit eine maßgebliche Rolle spielt. Aus den Versuchen zur Wellenlängenunterscheidungsfähigkeit kann des Weiteren abgeleitet werden, dass der ON-Kanal auch für die spektrale Empfindlichkeit der Tiere bei der gegebenen Beleuchtungs- und Dressurbedingungen (L+-Dressur) keine Bedeutung zu haben scheint. Nach den Versuchen zum kontrastabhängigen zeitlichen Auflösungsvermögen kann festgehalten werden, dass das zeitliche Auflösungsvermögen des Goldfisches sich mit abnehmendem Stimuluskontrast verändert: Der für die Tiere wahrnehmbare Flickerfrequenzbereich wird mit abnehmendem Kontrast geringer. Die Flimmerfusionsfrequenz wird im oberen Frequenzbereich früher erreicht; im unteren Flickerfrequenzbereich tritt mit abnehmendem Kontrast auch eine untere Grenze des zeitlichen Auflösungsvermögens auf. Des Weiteren zeigen die Ergebnisse aus den Verhaltensversuchen zu den kontrastabhängigen zeitlichen Übertragungseigenschaften eine gute Vergleichbarkeit zu elektrophysiologisch gewonnenen Antworten von ON bzw. OFF-Bipolarzellen. Ebenso ähneln sich die Kurvenverläufe zum kontrastabhängigen zeitlichen Auflösungsvermögen und die aus den Versuchen zur kontrastabhängigen Ganzfeldbewegungswahrnehmung – einer visuellen Leistung, deren Prozessierung eines ON-Kanal-Beitrages bedarf. Diese Ergebnisse deuten darauf hin, dass das zeitliche Auflösungsvermögen wie auch die Ganzfeldbewegungswahrnehmung hauptsächlich von retinalen Verarbeitungsprozessen abhängen.

Vergleich der retinalen und dermalen mikrovaskulären endothelialen Funktion bei Gesunden, Insulinresistenten und Typ-2-Diabetikern

Die vorliegende klinische Studie hatte zum Ziel, die mikrovaskuläre Endothelfunktion retinaler und dermaler Gefäße von Insulinresistenten und Typ 2- Diabetikern ohne Zeichen einer diabetischen Retinopathie mit einer gesunden insulinsensitiven nicht-diabetischen Kontrollgruppe hinsichtlich früher morphologischer und funktioneller Veränderungen zu vergleichen.rnrnMethode:rnEs wurden 54 Patienten ohne Nachweis einer diabetischen Retinopathie eingeschlossen und in 3 Gruppen entsprechend ihren metabolischen Ergebnissen eingeteilt: 1.) Gruppe K (Kontrollgruppe) setzte sich aus gesunden, nicht-diabetischen, insulin-sensitiven rn(HOMA ≤ 2) Probanden mit einem BMI ≤ 28 kg/m2 zusammen; 2.) Gruppe IR bestand aus den nicht-diabetischen, insulin-resistenten (HOMAs > 2), übergewichtigen Patienten mit einem BMI > 28 kg/m2 und 3.) Gruppe DM war definiert als Patienten mit einem manifesten Typ 2-Diabetes mellitus.rnrnDie mikrovaskuläre Funktion der Retina wurde mittels eines Laserdoppler-Verfahrens (Heidelberg Retina Flowmeter) untersucht und hierbei der retinale Blutfluss und das Verhältnis der Gefäßwand zum Lumen (WLR, wall-to-lumen-ratio) basal und nach Flickerlicht-Stimulation (10 Hz, Photo Stimulator 750) gemessen. Letzterer gilt als Marker für vaskuläre Schädigung. rnZusätzlich wurde die dermale Mikrozirkulation (Blutfluss, O2-Sättigung) als weiterer Faktor der mikrovaskulären Endothelfunktion in den 3 Studiengruppen untersucht und miteinander verglichen.rnErgebnisse:rnEs zeigte sich kein signifikanter Unterschied des retinalen Blutflusses zwischen den 3 Gruppen weder basal noch nach Flickerlicht-Stimulation. Es zeigte sich keine Korrelation zwischen der mikrovaskulären Funktion der Haut und der Retina. rnDie arterielle WLR zeigte nur geringe Unterscheide zwischen den 3 Gruppen.rnrnMit zunehmendem Grad der Insulinresistenz wurde jedoch eine Reduktion des basalen als auch des flickerlicht-stimulierten retinalen Blutflusses deutlich, dabei zeigte sich unerwarteter Weise eine Abnahme der WLR.rnrnDer (prä-ischämische) muskuläre Blutfluss war in der IR-Gruppe signifikant geringer als in der K-Gruppe. Auch war die postischämische dermale O2-Sättigung in der DM und IR-Gruppe signifikant niedriger im Vergleich zur K-Gruppe. Jedoch war die postischämische hyperämische dermale Reaktion in der IR und DM-Gruppe nur geringgradig weniger als in der K-Gruppe. rnrnSchlussfolgerung:rnEine Korrelation zwischen der Entwicklung der Insulinresistenz und retinaler sowie dermaler mikrovaskulärer endothelialer Funktion wurde bei der Studie deutlich. Mithilfe des neuen Verfahrens der Laser Scanner Flowmeter zur Messung der retinalen Endothelfunktion lassen sich sehr frühe morphologische Veränderungen des mikrovaskulären Blutflusses erfassen. rnDie fehlende Korrelation zwischen retinaler und dermaler mikrovaskulärer Funktion als auch die geringen Unterschiede der WLR sollte Gegenstand weiterer Studien seinrn

Detecting offsets in GPS time series: first results from the Detection of Offsets in GPS Experiment

The accuracy of Global Positioning System (GPS) time series is degraded by the presence of offsets. To assess the effectiveness of methods that detect and remove these offsets, we designed and managed the Detection of Offsets in GPS Experiment. We simulated time series that mimicked realistic GPS data consisting of a velocity component, offsets, white and flicker noises (1/f spectrum noises) composed in an additive model. The data set was made available to the GPS analysis community without revealing the offsets, and several groups conducted blind tests with a range of detection approaches. The results show that, at present, manual methods (where offsets are hand picked) almost always give better results than automated or semi‒automated methods (two automated methods give quite similar velocity bias as the best manual solutions). For instance, the fifth percentile range (5% to 95%) in velocity bias for automated approaches is equal to 4.2 mm/year (most commonly ±0.4 mm/yr from the truth), whereas it is equal to 1.8 mm/yr for the manual solutions (most commonly 0.2 mm/yr from the truth). The magnitude of offsets detectable by manual solutions is smaller than for automated solutions, with the smallest detectable offset for the best manual and automatic solutions equal to 5 mm and 8 mm, respectively. Assuming the simulated time series noise levels are representative of real GPS time series, robust geophysical interpretation of individual site velocities lower than 0.2–0.4 mm/yr is therefore certainly not robust, although a limit of nearer 1 mm/yr would be a more conservative choice. Further work to improve offset detection in GPS coordinates time series is required before we can routinely interpret sub‒mm/yr velocities for single GPS stations.

The temporal impulse response function in infantile nystagmus.

Despite rapid to-and-fro motion of the retinal image that results from their incessant involuntary eye movements, persons with infantile nystagmus (IN) rarely report the perception of motion smear. We performed two experiments to determine if the reduction of perceived motion smear in persons with IN is associated with an increase in the speed of the temporal impulse response. In Experiment 1, increment thresholds were determined for pairs of successively presented flashes of a long horizontal line, presented on a 65-cd/m2 background field. The stimulus-onset asynchrony (SOA) between the first and second flash varied from 5.9 to 234 ms. In experiment 2, temporal contrast sensitivity functions were determined for a 3-cpd horizontal square-wave grating that underwent counterphase flicker at temporal frequencies between 1 and 40 Hz. Data were obtained for 2 subjects with predominantly pendular IN and 8 normal observers in Experiment 1 and for 3 subjects with IN and 4 normal observers in Experiment 2. Temporal impulse response functions (TIRFs) were estimated as the impulse response of a linear second-order system that provided the best fit to the increment threshold data in Experiment 1 and to the temporal contrast sensitivity functions in Experiment 2. Estimated TIRFs of the subjects with pendular IN have natural temporal frequencies that are significantly faster than those of normal observers (ca. 13 vs. 9 Hz), indicating an accelerated temporal response to visual stimuli. This increase in response speed is too small to account by itself for the virtual absence of perceived motion smear in subjects with IN, and additional neural mechanisms are considered.

Reporting standards for studies of diagnostic test accuracy in dementia: The STARDdem Initiative.

OBJECTIVE To provide guidance on standards for reporting studies of diagnostic test accuracy for dementia disorders. METHODS An international consensus process on reporting standards in dementia and cognitive impairment (STARDdem) was established, focusing on studies presenting data from which sensitivity and specificity were reported or could be derived. A working group led the initiative through 4 rounds of consensus work, using a modified Delphi process and culminating in a face-to-face consensus meeting in October 2012. The aim of this process was to agree on how best to supplement the generic standards of the STARD statement to enhance their utility and encourage their use in dementia research. RESULTS More than 200 comments were received during the wider consultation rounds. The areas at most risk of inadequate reporting were identified and a set of dementia-specific recommendations to supplement the STARD guidance were developed, including better reporting of patient selection, the reference standard used, avoidance of circularity, and reporting of test-retest reliability. CONCLUSION STARDdem is an implementation of the STARD statement in which the original checklist is elaborated and supplemented with guidance pertinent to studies of cognitive disorders. Its adoption is expected to increase transparency, enable more effective evaluation of diagnostic tests in Alzheimer disease and dementia, contribute to greater adherence to methodologic standards, and advance the development of Alzheimer biomarkers.

The Quiet Eye and Information Processing: Facilitation of Stimulus Identification and Response Selection

Background: A prerequisite for high performance in motor tasks is the acquisition of egocentric sensory information that must be translated into motor actions. A phenomenon that supports this process is the Quiet Eye (QE) defined as long final fixation before movement initiation. It is assumed that the QE facilitates information processing, particularly regarding movement parameterization. Aims: The question remains whether this facilitation also holds for the information-processing stage of response selection and – related to perception crucial – stage of stimulus identification. Method: In two experiments with sport science students, performance-enhancing effects of experimentally manipulated QE durations were tested as a function of target position predictability and target visibility, thereby selectively manipulating response selection and stimulus identification demands, respectively. Results: The results support the hypothesis of facilitated information processing through long QE durations since in both experiments performance-enhancing effects of long QE durations were found under increased processing demands only. In Experiment 1, QE duration affected performance only if the target position was not predictable and positional information had to be processed over the QE period. In Experiment 2, in a full vs. no target visibility comparison with saccades to the upcoming target position induced by flicker cues, the functionality of a long QE duration depended on the visual stimulus identification period as soon as the interval falls below a certain threshold. Conclusions: The results corroborate earlier findings that QE efficiency depends on demands put on the visuomotor system, thereby furthering the assumption that the phenomenon supports the processes of sensorimotor integration.

Crustal uplift rates of 4 GPS stations near Jakobshavn Isbrae (2006-2009)

We analyze 2006-2009 data from four continuous Global Positioning System (GPS) receivers located between 5 and 150 km from the glacier Jakobshavn Isbrae, West Greenland. The GPS stations were established on bedrock to determine the vertical crustal motion due to the unloading of ice from Jakobshavn Isbrae. All stations experienced uplift, but the uplift rate at Kangia North, only 5 km from the glacier front, was about 10 mm/yr larger than the rate at Ilulissat, located only ~45 km further away. This suggests that most of the uplift is due to the unloading of the Earth's surface as Jakobshavn thins and loses mass. Our estimate of Jakobshavn's contribution to uplift rates at Kangia North and Ilulissat are 14.6 ± 1.7 mm/yr and 4.9 ± 1.1 mm/yr, respectively. The observed rates are consistent with a glacier thinning model based on repeat altimeter surveys from NASA's Airborne Topographic Mapper (ATM), which shows that Jakobshavn lost mass at an average rate of 22 ± 2 km**3/yr between 2006 and 2009. At Kangia North and Ilulissat, the predicted uplift rates computed using thinning estimates from the ATM laser altimetry are 12.1 ± 0.9 mm/yr and 3.2 ± 0.3 mm/yr, respectively. The observed rates are slightly larger than the predicted rates. The fact that the GPS uplift rates are much larger closer to Jakobshavn than further away, and are consistent with rates inferred using the ATM-based glacier thinning model, shows that GPS measurements of crustal motion are a potentially useful method for assessing ice-mass change models.

Kinematic pattern of the drag-flick: a case study

The drag-flick is more efficient than hits or pushes when a penalty corner situation is in effect in field hockey. Previous research has studied the biomechanical pattern of the drag-flick, trying to find the cues for an optimal performance. On the other hand, some other studies have examined the most effective visual pick-up of relevant information in shots and goalkeeper anticipation. The aim of this study was to analyse the individual differences in the drag-flick pattern in order to provide relevant information for goalkeepers. One female skilled drag-flicker participated in the study. A VICON optoelectronic sy stem (Oxford Metrics, Oxford, UK) was used to capture the drag-flicks with six cameras. The results showed that the main significant differences between right and left shots (p<0.05) in the stick angles, stick minimum angular velocity and front foot-ball distance were when the front foot heel contacted the floor(T1) and at the minimum velocity of the stick, before the dragging action (T3). The findings showed that the most relevant information might be picked up at the ball-and-stick location before the dragging action.

Contribución al diseño de lazos de realimentación electrónica para microsistemas electromecánicos (MEMS) resonantes: ruido de fase generado en lazos osciladores por sus realimentaciones

En 1966, D. B. Leeson publicó el artículo titulado “A simple model of feedback oscillator noise spectrum” en el que, mediante una ecuación obtenida de forma heurística y basada en parámetros conocidos de los osciladores, proponía un modelo para estimar el espectro de potencia que cuantifica el Ruido de Fase de estos osciladores. Este Ruido de Fase pone de manifiesto las fluctuaciones aleatorias que se producen en la fase de la señal de salida de cualquier oscilador de frecuencia f_0. Desde entonces, los adelantos tecnológicos han permitido grandes progresos en cuanto a la medida del Ruido de Fase, llegando a encontrar una estrecha “zona plana”, alrededor de f_0, conocida con el nombre de Ensanchamiento de Línea (EL) que Leeson no llegó a observar y que su modelo empírico no recogía. Paralelamente han ido surgiendo teorías que han tratado de explicar el Ruido de Fase con mayor o menor éxito. En esta Tesis se propone una nueva teoría para explicar el espectro de potencia del Ruido de Fase de un oscilador realimentado y basado en resonador L-C (Inductancia-Capacidad). Al igual que otras teorías, la nuestra también relaciona el Ruido de Fase del oscilador con el ruido térmico del circuito que lo implementa pero, a diferencia de aquellas, nuestra teoría se basa en un Modelo Complejo de ruido eléctrico que considera tanto las Fluctuaciones de energía eléctrica asociadas a la susceptancia capacitiva del resonador como las Disipaciones de energía eléctrica asociadas a su inevitable conductancia G=1⁄R, que dan cuenta del contacto térmico entre el resonador y el entorno térmico que le rodea. En concreto, la nueva teoría que proponemos explica tanto la parte del espectro del Ruido de Fase centrada alrededor de la frecuencia portadora f_0 que hemos llamado EL y su posterior caída proporcional a 〖∆f〗^(-2) al alejarnos de f_0, como la zona plana o pedestal que aparece en el espectro de Ruido de Fase lejos de esa f_0. Además, al saber cuantificar el EL y su origen, podemos explicar con facilidad la aparición de zonas del espectro de Ruido de Fase con caída 〖∆f〗^(-3) cercanas a la portadora y que provienen del denominado “exceso de ruido 1⁄f” de dispositivos de Estado Sólido y del ruido “flicker” de espectro 1⁄f^β (0,8≤β≤1,2) que aparece en dispositivos de vacío como las válvulas termoiónicas. Habiendo mostrado que una parte del Ruido de Fase de osciladores L-C realimentados que hemos denominado Ruido de Fase Térmico, se debe al ruido eléctrico de origen térmico de la electrónica que forma ese oscilador, proponemos en esta Tesis una nueva fuente de Ruido de Fase que hemos llamado Ruido de Fase Técnico, que se añadirá al Térmico y que aparecerá cuando el desfase del lazo a la frecuencia de resonancia f_0 del resonador no sea 0° o múltiplo entero de 360° (Condición Barkhausen de Fase, CBF). En estos casos, la modulación aleatoria de ganancia de lazo que realiza el Control Automático de Amplitud en su lucha contra ruidos que traten de variar la amplitud de la señal oscilante del lazo, producirá a su vez una modulación aleatoria de la frecuencia de tal señal que se observará como más Ruido de Fase añadido al Térmico. Para dar una prueba empírica sobre la existencia de esta nueva fuente de Ruido de Fase, se diseñó y construyó un oscilador en torno a un resonador mecánico “grande” para tener un Ruido de Fase Térmico despreciable a efectos prácticos. En este oscilador se midió su Ruido de Fase Técnico tanto en función del valor del desfase añadido al lazo de realimentación para apartarlo de su CBF, como en función de la perturbación de amplitud inyectada para mostrar sin ambigüedad la aparición de este Ruido de Fase Técnico cuando el lazo tiene este fallo técnico: que no cumple la Condición Barkhausen de Fase a la frecuencia de resonancia f_0 del resonador, por lo que oscila a otra frecuencia. ABSTRACT In 1966, D. B. Leeson published the article titled “A simple model of feedback oscillator noise spectrum” in which, by means of an equation obtained heuristically and based on known parameters of the oscillators, a model was proposed to estimate the power spectrum that quantifies the Phase Noise of these oscillators. This Phase Noise reveals the random fluctuations that are produced in the phase of the output signal from any oscillator of frequencyf_0. Since then, technological advances have allowed significant progress regarding the measurement of Phase Noise. This way, the narrow flat region that has been found around f_(0 ), is known as Line Widening (LW). This region that Leeson could not detect at that time does not appear in his empirical model. After Leeson’s work, different theories have appeared trying to explain the Phase Noise of oscillators. This Thesis proposes a new theory that explains the Phase Noise power spectrum of a feedback oscillator around a resonator L-C (Inductance-Capacity). Like other theories, ours also relates the oscillator Phase Noise to the thermal noise of the feedback circuitry, but departing from them, our theory uses a new, Complex Model for electrical noise that considers both Fluctuations of electrical energy associated with the capacitive susceptance of the resonator and Dissipations of electrical energy associated with its unavoidable conductance G=1/R, which accounts for the thermal contact between the resonator and its surrounding environment (thermal bath). More specifically, the new theory we propose explains both the Phase Noise region of the spectrum centered at the carrier frequency f_0 that we have called LW and shows a region falling as 〖∆f〗^(-2) as we depart from f_0, and the flat zone or pedestal that appears in the Phase Noise spectrum far from f_0. Being able to quantify the LW and its origin, we can easily explain the appearance of Phase Noise spectrum zones with 〖∆f〗^(-3) slope near the carrier that come from the so called “1/f excess noise” in Solid-State devices and “flicker noise” with 1⁄f^β (0,8≤β≤1,2) spectrum that appears in vacuum devices such as thermoionic valves. Having shown that the part of the Phase Noise of L-C oscillators that we have called Thermal Phase Noise is due to the electrical noise of the electronics used in the oscillator, this Thesis can propose a new source of Phase Noise that we have called Technical Phase Noise, which will appear when the loop phase shift to the resonance frequency f_0 is not 0° or an integer multiple of 360° (Barkhausen Phase Condition, BPC). This Phase Noise that will add to the Thermal one, comes from the random modulation of the loop gain carried out by the Amplitude Automatic Control fighting against noises trying to change the amplitude of the oscillating signal in the loop. In this case, the BPC failure gives rise to a random modulation of the frequency of the output signal that will be observed as more Phase Noise added to the Thermal one. To give an empirical proof on the existence of this new source of Phase Noise, an oscillator was designed and constructed around a “big” mechanical resonator whose Thermal Phase Noise is negligible for practical effects. The Technical Phase Noise of this oscillator has been measured with regard to the phase lag added to the feedback loop to separate it from its BPC, and with regard to the amplitude disturbance injected to show without ambiguity the appearance of this Technical Phase Noise that appears when the loop has this technical failure: that it does not fulfill the Barkhausen Phase Condition at f_0, the resonance frequency of the resonator and therefore it is oscillating at a frequency other than f_0.