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With the ever-growing interest in the area of mobile information retrieval and the ongoing fast development of mobile devices and, as a consequence, mobile apps, an active research area lies in studying users' behavior and search queries users submit on mobile devices. However, many researchers require to develop an app that collects useful information from users while they search on their phones or participate in a user study. In this paper, we aim to address this need by providing a comprehensive Android app, called Omicron, which can be used to collect mobile query logs and perform user studies on mobile devices. Omicron, at its current version, can collect users' mobile queries, relevant documents, sensor data as well as user activity and interaction data in various study settings. Furthermore, we designed Omicron in such a way that it is conveniently extendable to conduct more specific studies and collect other types of sensor data. Finally, we provide a tool to monitor the participants and their data both during and after the collection process., Comment: To appear in ACM CHIIR 2020, Vancouver, BC, Canada

Microscopies have become pillars of our characterization tools to observe biological systems and assemblies. Correlative and synchronous use of different microscopies relies on the fundamental assumption of non-interference during images acquisitions. In this work, by exploring the correlative use of Atomic Force Microscopy and confocal-Fluorescence-Lifetime Imaging Microscopy (AFM-FLIM), we quantify cross-talk effects occurring during synchronous acquisition. We characterize and minimize optomechanical forces on different AFM cantilevers interfering with normal AFM operation as well as spurious luminescence from the tip and cantilever affecting time-resolved fluorescence detection. By defining non-interfering experimental imaging parameters, we show accurate real-time acquisition and two-dimensional mapping of interaction force, fluorescence lifetime and intensity characterizing morphology (AFM) and local viscosity (FLIM) of gel and fluid phases separation of supported lipid model membranes. Finally, as proof of principle by means of synchronous force and fluorescence spectroscopies, we precisely tune the lifetime of a fluorescent nanodiamond positioned on the AFM tip by controlling its distance from a metallic surface. This opens up a novel pathway of quench sensing to image soft biological samples such as membranes since it does not require tip-sample mechanical contact in contrast with conventional AFM in liquid.

Improvements in mobile technologies have led to a dramatic change in how and when people access and use information, and is having a profound impact on how users address their daily information needs. Smart phones are rapidly becoming our main method of accessing information and are frequently used to perform `on-the-go' search tasks. As research into information retrieval continues to evolve, evaluating search behaviour in context is relatively new. Previous research has studied the effects of context through either self-reported diary studies or quantitative log analysis; however, neither approach is able to accurately capture context of use at the time of searching. In this study, we aim to gain a better understanding of task relevance and search behaviour via a task-based user study (n=31) employing a bespoke Android app. The app allowed us to accurately capture the user's context when completing tasks at different times of the day over the period of a week. Through analysis of the collected data, we gain a better understanding of how using smart phones on the go impacts search behaviour, search performance and task relevance and whether or not the actual context is an important factor., Comment: To appear in CHIIR 2019 in Glasgow, UK

Recently, using an Atomic Force Microscope and a single cantilever excited at different frequencies it was shown that water nanomeniscus can exhibit a transition in mechanical responses when submitted to stimuli above few tens of kHz. The use of a single cantilever to explore phenomena at frequencies far from the cantilever resonance frequency is not a common and well-established strategy, and because water meniscus are ubiquitous in nature, we have also studied the water meniscus mechanical response, the stiffness G' (N/m) and the dissipation G"(kg/s), as a function of frequency by using cantilevers with different resonance frequencies. These results, based on classic dynamical AFM technics, confirm the anomalous mechanical response of water nanomeniscus when stimulated at frequencies high enough.

We report the observation of a transition in the dynamical properties of water nano-menicus which dramatically change when probed at different time scales. Using a AFM mode that we name Force Feedback Microscopy, we observe this change in the simultaneous measurements, at different frequencies, of the stiffness G'(N/m), the dissipative coefficient G''(kg/sec) together with the static force. At low frequency we observe a negative stiffness as expected for capillary forces. As the measuring time approaches the microsecond, the dynamic response exhibits a transition toward a very large positive stiffness. When evaporation and condensation gradually lose efficiency, the contact line progressively becomes immobile. This transition is essentially controlled by variations of Laplace pressure.

Quantifying the tip-sample interaction at the nanoscale in Amplitude Modulation mode AFM is challenging, especially when measuring in liquids. Here, we derive formulas for the tip-sample conservative and dissipative interactions and investigate the effect that spurious resonances have on the measured interaction. Both direct and acoustic excitation are considered. We also highlight the differences between measuring directly the tip position or the cantilever deflection. We show that, when probing the tip-sample forces, the acoustically excited cantilever behavior is insensitive to spurious resonances as long as the measured signal corresponds to the tip position, or if the excitation force is correctly taken into account. Since the effective excitation force may depend on the presence of such spurious resonances, we consider the cases where the frequency is kept constant during the measurement so that the proportionality between excitation signal and actual excitation force is kept constant. With the present work we show the advantages that result from the use of a calibration method based on the acquisition of approach-retract curves. Optical beam deflection based AFMs benefit from the use of this calibration method, especially in presence of spurious resonances in the cantilever transfer function.

It was shown recently that the Force Feedback Microscope can avoid the jump-to-contact in Atomic force Microscopy even when the cantilevers used are very soft, thus increasing force resolution. In this letter, we explore theoretical aspects of the associated real time control of the tip position. We take into account lever parameters such as the lever characteristics in its environment, spring constant, mass, dissipation coefficient and the operating conditions such as controller gains, and interaction force. We show how the controller parameters are determined so that the FFM functions at its best and estimate the bandwidth of the system under these conditions.

The mechanical properties of PC12 living cells have been studied at the nanoscale with a Force Feedback Microscope using two experimental approaches. Firstly, the local mechanical impedance of the cell membrane has been mapped simultaneously to the cell morphology at constant force. As the force of the interaction is gradually increased, we observed the appearance of the sub-membrane cytoskeleton. We shall compare the results obtained with this method with the measurement of other existing techniques. Secondly, a spectroscopic investigation has been performed varying the indentation of the tip in the cell membrane and consequently the force applied on it. In contrast with conventional dynamic atomic force microscopy techniques, here the small oscillation amplitude of the tip is not necessarily imposed at the cantilever first eigenmode. This allows the user to arbitrarily choose the excitation frequency in developing spectroscopic AFM techniques. The mechanical response of the PC12 cell membrane is found to be frequency dependent in the 1 kHz - 10 kHz range. The damping coefficient is reproducibly observed to decrease when the excitation frequency is increased., Comment: 8 pages, 8 figures

Atomic Force Microscopy (AFM) conventional static force curves and Force Feedback Microscopy (FFM) force curves acquired with the same cantilever at the solid/air and solid/liquid interfaces are here compared. The capability of the FFM to avoid the jump to contact leads to the complete and direct measurement of the interaction force curve, including the attractive short-range van der Waals and chemical contributions. Attractive force gradients five times higher than the lever stiffness do not affect the stability of the FFM static feedback loop. The feedback loop keeps the total force acting on the AFM tip equal to zero, allowing the use of soft cantilevers as force transducers to increase the instrumental sensitivity. The attractive interactions due to the nucleation of a capillary bridge at the native oxide silicon/air interface or due to a DLVO interaction at the mica/deionized water interface have been measured. This set up, suitable for measuring directly and quantitatively interfacial forces, can be exported to a SFA (Surface Force Apparatus)., Comment: 5 pages, 4 figures

Mechanical properties of biological samples have been imaged with a \textit{Force Feedback Microscope}. Force, force gradient and dissipation are measured simultaneously and quantitatively, merely knowing the AFM cantilever spring constant. Our first results demonstrate that this robust method provides quantitative high resolution force measurements of the interaction The little oscillation imposed to the cantilever and the small value of its stiffness result in a vibrational energy much smaller than the thermal energy, reducing the interaction with the sample to a minimum. We show that the observed mechanical properties of the sample depend on the force applied by the tip and consequently on the sample indentation. Moreover, the frequency of the excitation imposed to the cantilever can be chosen arbitrarily, opening the way to frequency-dependent studies in biomechanics, sort of spectroscopic AFM investigations.

The force between two interacting particles as a function of distance is one of the most fundamental curves in science. In this regard, Atomic Force Microscopy (AFM) represents the most powerful tool in nanoscience but with severe limits when it is to probe attractive interactions with high sensitivity. The Force Feedback Microscope (FFM) described here, removes from AFM the well known jump to contact problem that precludes the complete exploration of the interaction curve and the study of associated energy exchanges. The FFM makes it possible to explore tip-surface interactions in the entire range of distances with a sensitivity better than 1 pN. FFM stands out as a radical change in AFM control paradigms. With a surprisingly simple arrangement it is possible to provide the AFM tip with the right counterforce to keep it fixed at any time. The counterforce is consequently equal to the tip-sample force. The force, force gradient and damping are simultaneously measured independently of the tip position. This permits the measurement of energy transfer in thermodynamic transformations. Here we show some FFM measurement examples of the complete interaction force curve and in particular that the FFM can follow the nucleation of a water bridge by measuring the capillary attractive force at all distances, without jump to contact despite the large attractive capillary force. Real time combination of the measured parameters will lead to new imaging modalities with chemical contrast in different environments., Comment: 4 pages, 4 figures