Abstract: Identifying a test pattern includes positioning a test pattern that includes a first multiplicity of particles that reflect or emit light in the field of view of a first imaging device; illuminating the test pattern with light from a first light source; obtaining, with the first imaging device, a first test image of light reflected by the first multiplicity of particles; and comparing the first test image with a first reference image of a reference pattern obtained by a second imaging device.

Abstract: Disclosed are methods and systems that include obtaining at least one image of a dendritic structure, analyzing the at least one image to identify one or more features associated with the dendritic structure, and determining a numerical value associated with the dendritic structure based on the one or more features.

Abstract: Assessing the authenticity of a dendrite on a substrate includes illuminating the dendrite and the substrate with radiation, obtaining a first image of the dendrite on the substrate at a first polarization angle, obtaining a second image of the dendrite on the substrate at a second polarization angle, and assessing a difference in intensity of a multiplicity of corresponding pixels of the candidate structure in the first image and the second image. If the difference in intensity of each pair of pixels of the multiplicity of corresponding pixels exceeds a preselected value, the dendrite is identified as authentic.

Abstract: Assessing distortion of a dendrite includes obtaining an optical image of the dendrite, assessing geometric features of the dendrite based on the optical image, comparing the geometric features of the dendrite to corresponding geometric features of a corresponding undistorted dendrite, assessing a distortion of the geometric features of the dendrite relative to the corresponding geometric features of the corresponding undistorted dendrite, and identifying the dendrite as distorted if the distortion exceeds a threshold value. The geometric features can include branches, angles between branches, and thicknesses of branches. The distortion can include alteration of a length of a branch of the dendrite, alteration of an angle between branches of the dendrite, alteration in a thickness of a branch of the dendrite, or a discontinuity in a branch of the dendrite. Obtaining the optical image comprises irradiating the dendrite with polarized or unpolarized light.

Abstract: Forming a unique stochastically branching pattern includes providing a first fluid between a surface of a first substrate and a surface of a second substrate and introducing a second fluid between the surface of the first substrate and the surface of the second substrate. The second fluid is in direct contact with the first fluid at a formation temperature, and a viscosity of the first fluid at the formation temperature exceeds a viscosity of the second fluid at the formation temperature. The first substrate and the second substrate are separated to yield a unique stochastically branching pattern comprising the first fluid on the surface of the first substrate.

Abstract: Assessing corruption of a dendritic structure includes obtaining an image of a dendritic structure having a plurality of branches extending away from a common point of the dendritic structure and defining a stochastic arrangement of branches, and assessing, based on the image, whether an arrangement of one or more of the branches violates a formation role governing formation of the dendritic structure.

Abstract: Assessing corruption of a dendritic structure includes obtaining an image of a dendritic structure having a plurality of branches extending away from a common point of the dendritic structure and defining a stochastic arrangement of branches, and assessing, based on the image, whether an arrangement of one or more of the branches violates a formation rule governing formation of the dendritic structure.

Abstract: Methods for fabricating dendritic structures and tags include introducing an electrolyte material onto a substrate, into a substrate, or both onto and into a substrate, and applying an electrical potential to at least one pair of electrodes positioned on the substrate to form one or more dendritic structures on the substrate.

Abstract: A low-voltage microfluidic valve device and system for regulating the flow of fluid. One low-voltage microfluidic valve device for regulating the low of fluid includes a nano-textured dendritic metallic filament configured to grow and retract in response to a voltage. The low-voltage microfluidic valve device also includes a microfluidic channel configured to allow fluid flow, wherein the fluid flow is selectively interrupted by the growth of the nano-textured dendritic metallic filament. The low-voltage microfluidic valve device also includes a membrane positioned proximate to the fluid and configured to alter shape in response to the growth of the nano-textured dendritic metallic filament.

Abstract: The disclosure features methods and systems that include illuminating a candidate structure with radiation linearly polarized along a first polarization direction and obtaining a first image of the dendritic structure, illuminating the candidate structure with radiation linearly polarized along a second polarization direction and obtaining a second image of the dendritic structure, where an angle between the first and second polarization directions is at least 10, for a set of pixels corresponding to a first region of the candidate structure in the first and second images, determining a first change in average pixel intensity between the first and second images, and authenticating the candidate structure as a dendritic structure based on the first change in average pixel intensity.

Abstract: The disclosure features dendritic tags, and methods and systems for fabricating and using such tags. The methods can include obtaining at least one image of a dendritic tag attached to an article, analyzing the at least one image to identify a set of features associated with the dendritic tag, and comparing the set of features to stored information to identify the article.

Abstract: Preparing a dendritic tag includes forming a liquid composition including dendrites, separating the dendrites from the liquid composition, and disposing the dendrites on a substrate. In some cases, the composition is applied to a substrate and the liquid is evaporated to yield at least one dendrite in direct contact with the substrate. A labeled item includes an item and a dendritic tag coupled to the item, such that the item can be identified or authenticated based on a property of the dendritic tag.

Abstract: The disclosure features dendritic tags, and methods and systems for fabricating and using such tags. The methods can include obtaining at least one image of a dendritic tag attached to an article, analyzing the at least one image to identify a set of features associated with the dendritic tag, and comparing the set of features to stored information to identify the article.

Abstract: Disclosed are methods and systems that include obtaining at least one image of a dendritic structure, analyzing the at least one image to identify one or more features associated with the dendritic structure, and determining a numerical value associated with the dendritic structure based on the one or more features.

Abstract: Methods for fabricating dendritic structures and tags include introducing an electrolyte material onto a substrate, into a substrate, or both onto and into a substrate, and applying an electrical potential to at least one pair of electrodes positioned on the substrate to form one or more dendritic structures on the substrate.

Abstract: Allowing secure access to a computer system includes receiving an online access request from a user, selecting a dendritic identifier, associating selected information received in the online access request with the dendritic identifier, and providing the dendritic identifier to the user. Providing the dendritic identifier to the user can include sending (e.g., physically sending) the dendritic identifier to the user. Allowing secure access to the computer system can further include receiving information related to the dendritic identifier from the user, assessing the authenticity of the dendritic identifier based on the information received from the user, and if the authenticity of the dendritic identifier is verified, allowing the user access to the computer system.

Abstract: A low-voltage microfluidic valve device and system for regulating the flow of fluid. One low-voltage microfluidic valve device for regulating the low of fluid includes a nano-textured dendritic metallic filament configured to grow and retract in response to a voltage. The low-voltage microfluidic valve device also includes a microfluidic channel configured to allow fluid flow, wherein the fluid flow is selectively interrupted by the growth of the nano-textured dendritic metallic filament. The low-voltage microfluidic valve device also includes a membrane positioned proximate to the fluid and configured to alter shape in response to the growth of the nano-textured dendritic metallic filament.

Abstract: Disclosed are methods and systems that include obtaining at least one image of a dendritic structure, analyzing the at least one image to identify one or more features associated with the dendritic structure, and determining a numerical value associated with the dendritic structure based on the one or more features.

Abstract: The disclosure features dendritic tags, and methods and systems for fabricating and using such tags. The methods can include obtaining at least one image of a dendritic tag attached to an article, analyzing the at least one image to identify a set of features associated with the dendritic tag, and comparing the set of features to stored information to identify the article.

Abstract: A low-voltage microfluidic valve device and system for regulating the flow of fluid. One low-voltage microfluidic valve device for regulating the low of fluid includes a nano-textured dendritic metallic filament configured to grow and retract in response to a voltage. The low-voltage microfluidic valve device also includes a microfluidic channel configured to allow fluid flow, wherein the fluid flow is selectively interrupted by the growth of the nano-textured dendritic metallic filament. The low-voltage microfluidic valve device also includes a membrane positioned proximate to the fluid and configured to alter shape in response to the growth of the nano-textured dendritic metallic filament.