Noise characterization of an atomic magnetometer at sub-millihertz frequencies

Noise measurements have been carried out in the LISA bandwidth (0.1 mHz to 100 mHz) to characterize an all-optical atomic magnetometer based on nonlinear magneto-optical rotation. This was done in order to assess if the technology can be used for space missions with demanding low-frequency requirements like the LISA concept. Magnetometry for low-frequency applications is usually limited by $1/f$ noise and thermal drifts, which become the dominant contributions at sub-millihertz frequencies. Magnetic field measurements with atomic magnetometers are not immune to low-frequency fluctuations and significant excess noise may arise due to external elements, such as temperature fluctuations or intrinsic noise in the electronics. In addition, low-frequency drifts in the applied magnetic field have been identified in order to distinguish their noise contribution from that of the sensor. We have found the technology suitable for LISA in terms of sensitivity, although further work must be done to characterize the low-frequency noise in a miniaturized setup suitable for space missions.Comment: 11 pages, 12 figure

LISA pathfinder micronewton cold gas thrusters: in-flight characterization

The LISA Pathfinder (LPF) mission has demonstrated the ability to limit and measure the fluctuations in acceleration between two free falling test masses down to sub-femto-g levels. One of the key elements to achieve such a level of residual acceleration is the drag free control. In this scheme the spacecraft is used as a shield against any external disturbances by adjusting its relative position to a reference test mass. The actuators used to move the spacecraft are cold gas micropropulsion thrusters. In this paper, we report in-flight characterization of these thrusters in term of noise and artefacts during science operations using all the metrology capabilities of LISA Pathfinder. Using the LISA Pathfinder test masses as an inertial reference frame, an average thruster noise of ~0.17¿¿µN/Hz is observed and decomposed into a common (coherent) and an uncorrelated component. The very low noise and stability of the onboard metrology system associated with the quietness of the space environment allowed the measurement of the thruster noise down to ~20¿¿µHz, more than an order of magnitude below any ground measurement. Spectral lines were observed around ~1.5¿¿mHz and its harmonics and around 55 and 70 mHz. They are associated with the cold gas system itself and possibly to a clock synchronization issue. The thruster noise-floor exhibits an excess of ~70% compared to characterization that have been made on ground on a single unit and without the feeding system. However this small excess has no impact on the LPF mission performance and is compatible with the noise budget for the upcoming LISA gravitational wave observatory. Over the whole mission, nominal, and extension, the thrusters showed remarkable stability for both the science operations and the different maneuvers necessary to maintain LPF on its orbit around L1. It is therefore concluded that a similar cold gas system would be a viable propulsion system for the future LISA mission.Peer ReviewedPostprint (author's final draft

Novel methods to measure the gravitational constant in space

We present two novel methods, tested by LISA Pathfinder, to measure the gravitational constant G for the first time in space. Experiment 1 uses electrostatic suspension forces to measure a change in acceleration of a test mass due to a displaced source mass. Experiment 2 measures a change in relative acceleration between two test masses due to a slowly varying fuel tank mass. Experiment 1 gave a value of G=6.71±0.42(×10-11)¿¿m3¿s-2¿kg-1 and experiment 2 gave 6.15±0.35(×10-11)¿¿m3¿s-2¿kg-1, both consistent with each other to 1s and with the CODATA 2014 recommended value of 6.67408±0.00031(×10-11)¿¿m3¿s-2¿kg-1 to 2s. We outline several ideas to improve the results for a future experiment, and we suggest that a measurement in space would isolate many terrestrial issues that could be responsible for the inconsistencies between recent measurements.Peer ReviewedPostprint (published version

Temperature stability in the sub-milliHertz band with LISA Pathfinder

This article has been accepted for publication in "Monthly notices of the royal astronomical society" published by Oxford University Press.LISA Pathfinder (LPF) was a technology pioneering mission designed to test key technologies required for gravitational wave detection in space. In the low frequency regime (milliHertz and below), where space-based gravitational wave observatories will operate, temperature fluctuations play a crucial role since they can couple into the interferometric measurement and the test masses’ free-fall accuracy in many ways. A dedicated temperature measurement subsystem, with noise levels in 10¿µK¿Hz-1/2 down to 1¿mHz was part of the diagnostics unit onboard LPF. In this paper we report on the temperature measurements throughout mission operations, characterize the thermal environment, estimate transfer functions between different locations, and report temperature stability (and its time evolution) at frequencies as low as 10¿µHz, where typically values around 1¿K¿Hz-1/2 were measured.Peer ReviewedPreprin

Are Geoparks webpages attractive to potencial tourists? Some results of an evaluation procedure

This study evaluates the attractiveness and interest of the Geoparks webpages to potential tourists. The work is based on filling a table consisting of 67 criteria rated from 1 to 5. The criteria are arranged in groups of seven indicators. This study shows that most webpages do not appeal to those who seek information on Geoparks with the intent of selecting a tourist destination. Standing out as major problems are disorganisation and dispersion of information, as well as the absence of fundamental information for those seeking a tourist destinatio

Qualidade da manga e polpa da manga Ubá.

A manga Ubá (Mangifera indica L. variedade Ubá) possui excelentes qualidades de sabor e aroma, além de sua polpa ser amarelada, saborosa e suculenta. Contém teor de sólidos solúveis, em torno de 14 °Brix, acidez de 0,2% em ácido cítrico e ratio 70, além de ser rica em potássio e vitaminas A e C. A fruta possui fibras curtas e macias, podendo ser consumida ao natural e ser utilizada na industrialização, especialmente para elaboração de polpa e suco. Esta variedade possui excelente rendimento industrial por reduzir sensivelmente os custos de processamento durante o preparo, com conseqüente redução nos custos de produção. Para isso, determinou-se a qualidade da manga Ubá fornecida a uma agroindústria produtora de polpas e sucos na Região da Zona da Mata Mineira, com análises laboratoriais da fruta e da polpa. Durante a safra 2003/2004 as Mangas Sujas (MS), assim denominadas as frutas que chegavam à indústria, apresentaram contagem inicial média de 7,34 log UFC de mesófilos aeróbios/manga e após a higienização, denominadas de Mangas Higienizadas (MH), cuja média era de 5,62 log UFC/manga, apresentando redução média de 1,72 ciclos log. na safra 2004/2005, as MS apresentaram contagem inicial média de 7,02 log UFC de mesófilos aeróbios/manga e as MH, média de 5,76 log UFC/manga, apresentando redução média de 1,52 ciclos log. A polpa de manga apresentou valores para pH, sólidos solúveis totais, acidez total titulável, relação sólidos solúveis totais/acidez total titulável (ratio), sólidos totais e açúcares totais solúveis dentro dos exigidos pela legislação. As coordenadas de cor apresentaram valores indicando que a polpa possui cor característica amarelo-alaranjado. Quality of the fruits and pulp of Uba mango. Abstract: Uba mango (Mangifera indicates L. var. Uba) has excellent flavor qualities and a tasty, yellow and succulent pulp. It contains a high content of soluble solids, around 14 degrees Brix, acidity of 0.2% as citric acid and ratio 70, besides being rich in potassium and vitamins A and C. The fruit has soft and short fibers, and can be consumed fresh or be industrialized, especially for the production of pulp and juice. This variety possesses an excellent industrialization yield, by greatly reducing processing, with a consequent reduction in the final production costs. Uba mango supplied to a pulp and juice agroindustry in the Zona da Mata Mineira area had its quality determined through fruit and pulp analyses. During the 2003/2004 harvest period, the Dirty Mangos (DM), as were denominated the fruits that arrived at the industry, presented an average initial count of 7.34 log CFU mesophyllic aerobics/mango. After cleaning, the fruits were called Clean Mangos (CM), and had an average of 5.62 log CFU/mango, presenting an average reduction of 1.72 log cycles. In the 2004/2005 harvest period, the DM presented an average initial count of 7.02 log CFU mesophyllic aerobics/mango and the CM, an average of 5.76 log CFU/mango, with an average reduction of 1.52 log cycles. The mango pulp presented values for pH, total soluble solids, total acidity, total soluble solids/total acidity ratio, total solids and total soluble sugars, in accordance with the legislation requirements. The color coordinates presented values indicating that the pulp has a yellow-orange characteristic color

LISA Pathfinder platform stability and drag-free performance

The science operations of the LISA Pathfinder mission have demonstrated the feasibility of sub-femto-g free fall of macroscopic test masses necessary to build a gravitational wave observatory in space such as LISA. While the main focus of interest, i.e., the optical axis or the x-axis, has been extensively studied, it is also of great importance to evaluate the stability of the spacecraft with respect to all the other degrees of freedom (d.o.f.). The current paper is dedicated to such a study: the exhaustive and quantitative evaluation of the imperfections and dynamical effects that impact the stability with respect to its local geodesic. A model of the complete closed-loop system provides a comprehensive understanding of each component of the in-loop coordinates spectral density. As will be presented, this model gives very good agreement with LISA Pathfinder flight data. It allows one to identify the noise source at the origin and the physical phenomena underlying the couplings. From this, the stability performance of the spacecraft with respect to its geodesic is extracted as a function of frequency. Close to 1 mHz, the stability of the spacecraft on the XSC, YSC and ZSC d.o.f. is shown to be of the order of 5.0×10-15¿¿m¿s-2¿Hz-1/2 for X, 6.0×10-14¿¿m¿s-2¿Hz-1/2 for Y, and 4.0×10-14¿¿m¿s-2¿Hz-1/2 for Z. For the angular d.o.f., the values are of the order of 3×10-12¿¿rad¿s-2¿¿Hz-1/2 for TSC, 5×10-13¿¿rad¿s-2¿¿Hz-1/2 for HSC, and 3×10-13¿¿rad¿s-2¿¿Hz-1/2 for FSC. Below 1 mHz, however, the stability performances are worsened significantly by the effect of the star tracker noise on the closed-loop system. It is worth noting that LISA is expected to be spared from such concerns, as differential wave-front sensing, an attitude sensor system of much higher precision, will be utilized for attitude control.Peer ReviewedPostprint (author's final draft

LISA pathfinder performance confirmed in an open-loop configuration: results from the free-fall actuation mode

We report on the results of the LISA Pathfinder (LPF) free-fall mode experiment, in which the control force needed to compensate the quasistatic differential force acting on two test masses is applied intermittently as a series of "impulse" forces lasting a few seconds and separated by roughly 350 s periods of true free fall. This represents an alternative to the normal LPF mode of operation in which this balancing force is applied continuously, with the advantage that the acceleration noise during free fall is measured in the absence of the actuation force, thus eliminating associated noise and force calibration errors. The differential acceleration noise measurement presented here with the free-fall mode agrees with noise measured with the continuous actuation scheme, representing an important and independent confirmation of the LPF result. An additional measurement with larger actuation forces also shows that the technique can be used to eliminate actuation noise when this is a dominant factor.Peer ReviewedPostprint (published version

Gestión del trabajo colegiado en la academia de historia en un bachillerato

Proyecto de intervención realizado en la escuela preparatoria No. 9 de la Universidad de Guadalajara. El objetivo fue incrementar la eficacia y la calidad en la organización, funcionamiento y seguimiento del trabajo colegiado de la Academia de Historia del Departamento de Ciencias Histórico-Sociales, mediante la formación y capacitación de sus integrantes, con el propósito de que sean capaces de desarrollar habilidades para replantear sus actividades y rediseñar procesos académicos

Forbush decreases and <2 day GCR flux non-recurrent variations studied with LISA pathfinder

Non-recurrent short-term variations of the galactic cosmic-ray (GCR) flux above 70 MeV n-1 were observed between 2016 February 18 and 2017 July 3 on board the European Space Agency LISA Pathfinder (LPF) mission orbiting around the Lagrange point L1 at 1.5 × 106 km from Earth. The energy dependence of three Forbush decreases is studied and reported here. A comparison of these observations with others carried out in space down to the energy of a few tens of MeV n-1 shows that the same GCR flux parameterization applies to events of different intensity during the main phase. FD observations in L1 with LPF and geomagnetic storm occurrence are also presented. Finally, the characteristics of GCR flux non-recurrent variations (peaks and depressions) of duration <2 days and their association with interplanetary structures are investigated. It is found that, most likely, plasma compression regions between subsequent corotating high-speed streams cause peaks, while heliospheric current sheet crossing causes the majority of the depressions.Peer ReviewedPostprint (published version