This work was financially supported in part by The Light Metal Educational Foundation, Inc., Osaka, Japan

1. Material preparation
<ol>
	<li>Use 1 mm thick plates made of an aluminum-magnesium-silicon alloy containing 1 mass% Mg and 0.8 mass% Si (Al-Mg-Si).</li>
	<li>Make test pieces from the Al-Mg-Si alloy plates having a gauge length of 10 mm and width of 5 mm.</li>
	<li>Anneal the test pieces at 520 &#730;C for 1 h using an air furnace. Quench in water as a solution heat treatment.</li>
	<li>Anneal the test pieces at 175 &#730;C for 18 h as a peak aging heat treatment (T6-temper).</li>
	<li>Polish the surface of the test pieces using silicon carbide emery paper (#2000) without water.</li>
	<li>Measure the weight of the polished specimens to a precision of 0.0001 g using an electric balance</li>
	<li>Measure the thickness and width of the gauge part of the specimens to a precision of 0.001 mm using an optical comparator.</li>
</ol>
2. FW procedure (Figure 1)
<ol>
	<li>Attach two Al-Mg-Si alloy specimens using glue to a triangular, prism-shaped stirrer made by a fluorocarbon polymer.</li>
	<li>Prepare a cylinder glass container with an empty top as a reaction vessel.</li>
	<li>Attach a round polishing paper made by silicon carbides, #2000 with a diameter of 10 mm, using double sided tape in the bottom inside of the container.</li>
	<li>Place the triangular, prism-shaped stirrer with two specimens on the polishing paper at the bottom surface of the glass container.</li>
	<li>Pour 100 mL of distilled water into the glass container from the top.</li>
	<li>Cover the glass container with a round rubber piece with three holes (for a gas inlet, for a gas outlet, and for a pH probe at the top of the glass container).</li>
	<li>Fill the glass container with high purity (99.999%) argon at a constant flow rate of 20 mL/min after closing the rubber cover.</li>
	<li>Connect the gas outlet to a gas chromatograph (GC) with a semiconductor hydrogen sensor (detection limit: 5 ppb).</li>
	<li>Wait until the gas in the container is replaced by argon.</li>
	<li>Rotate the triangular, prism-shaped stirrer with two specimens on a magnetic stirrer with a constant rotating speed at room temperature.</li>
	<li>Measure the hydrogen generation during the stirrer rotation using the GC, taking one measurement every 2 min.</li>
	<li>Measure the pH of the water in the container during the stirrer rotation.</li>
	<li>Remove the two specimens from the triangular, prism-shaped stirrer by immersion in acetone with an ultrasonic vibration for 5 min after the FW procedure.</li>
	<li>Measure the weight and thickness of the specimens again after the FW procedure using the electric balance and an optical comparator, respectively.</li>
</ol>
3. Hydrogen absorption by the FW procedure
<ol>
	<li>After the FW procedure, cut a specimen to a rectangular shape of 1 x 5 x 10 mm.</li>
	<li>Place the specimen inside a quartz tube with a diameter of 10 mm connected to a GC with a semiconductor hydrogen sensor.</li>
	<li>Flow high purity (99.999%) argon gas in a quartz tube with a constant flow rate of 20 mL/min.</li>
	<li>Heat the quartz tube with the specimen using a tubular furnace at a constant heating rate, 200 &#730;C/h.</li>
	<li>Measure the thermal hydrogen desorption of the specimen after the FW procedure using the GC.</li>
</ol>
4. Material evaluation after the FW procedure
<ol>
	<li>Carry out tensile tests (at least 3x, to ensure repeatability) in laboratory air with a crosshead speed of 2 mm/min using a specimen that has been treated by the FW procedure.</li>
	<li>Measure the tensile properties (e.g., tensile strength, fracture strain) obtained from the stress-strain curve in the tensile test.</li>
	<li>Observe the fracture behavior with a secondary electron microscope (SEM) after the tensile test.</li>
</ol>

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The authors have nothing to disclose.

One important aspect of the FW procedure is the attachment of the two specimens to the magnetic stirrer. Because the center of the stirrer bar becomes the non-friction zone, it is best to avoid the attachment of the specimens at the center of the stirrer bar.
Control of the rotation speed of the stirrer bar is also important. When the speed is more than 240 rpm, it becomes difficult to maintain the reaction vessel on the stage of the magnetic stirrer. When the FW procedure is carried out at hi...

In general, aluminum base alloys have higher resistance to environmental hydrogen embrittlement than steel. The high resistance to hydrogen embrittlement of aluminum alloys is due to oxide films on the alloy surface blocking hydrogen entry. To evaluate and compare the high embrittlement sensitivity between aluminum alloys, hydrogen charging is usually performed prior to mechanical testing1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17. However, it is known that hydrogen charging aluminum is not easy, even when utilizing hydrogen charging methods such as cathodic charging15, slow strain rate deformation under humid air16, or hydrogen plasma gas charging17. The difficulty of hydrogen charging aluminum alloys is also due to the oxide films on the aluminum alloy surface. We postulated that higher amounts of hydrogen could be introduced into aluminum alloys if we could remove the oxide film continuously in water. Thermodynamically18, pure aluminum without oxide film reacts easily with water and generates hydrogen. Based on this, we have developed a new method of hydrogen charging of aluminum alloys based on the chemical reaction between water and non-oxide aluminum. This method is able to add high amounts of hydrogen into aluminum alloys in a simple way.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Air furnace</td>
			<td>GC</td>
			<td>QC-1</td>
			<td></td>
		</tr>
		<tr>
			<td>Aluminum alloy plates</td>
			<td>Kobe Steel</td>
			<td></td>
			<td>Al/1.0 mass% Mg/0.8 mass% Si</td>
		</tr>
		<tr>
			<td>Electric balance</td>
			<td>A&#38;D</td>
			<td>HR-200</td>
			<td></td>
		</tr>
		<tr>
			<td>Glass container</td>
			<td></td>
			<td></td>
			<td>Custom made</td>
		</tr>
		<tr>
			<td>Magnetic stirrer</td>
			<td>CORNING</td>
			<td>PC-410D</td>
			<td></td>
		</tr>
		<tr>
			<td>Optical Comparator</td>
			<td>NIKON</td>
			<td>V-12B</td>
			<td></td>
		</tr>
		<tr>
			<td>pH meter</td>
			<td>Sato Tech</td>
			<td>PH-230SDJ</td>
			<td></td>
		</tr>
		<tr>
			<td>Quartz tube</td>
			<td></td>
			<td></td>
			<td>Custom made</td>
		</tr>
		<tr>
			<td>Rotary polishing machine</td>
			<td>IMT</td>
			<td>IM-P2</td>
			<td></td>
		</tr>
		<tr>
			<td>Secondary electrom microscope</td>
			<td>JOEL</td>
			<td>JSM-5310LV</td>
			<td></td>
		</tr>
		<tr>
			<td>Sensor gas chromatograph</td>
			<td>FIS Inc.</td>
			<td>SGHA</td>
			<td></td>
		</tr>
		<tr>
			<td>Silicon carbide emery paper</td>
			<td>IMT</td>
			<td>531SR</td>
			<td></td>
		</tr>
		<tr>
			<td>Tensile testing machine</td>
			<td>Toshin Kogyo</td>
			<td>SERT-5000-C</td>
			<td></td>
		</tr>
		<tr>
			<td>Tubular furnace</td>
			<td>Honma Riken</td>
			<td></td>
			<td>Custom made</td>
		</tr>
	</tbody>
</table>

hydrogen charging of aluminum using friction in water

A new method of hydrogen charging of aluminum was developed by means of a friction in water (FW) procedure. This procedure can easily introduce high amounts of hydrogen into aluminum based on the chemical reaction between water and non-oxide coated aluminum.

Hydrogen generation/absorption by the FW procedure 
Figure 2 shows the hydrogen generation behavior during the FW procedure of Al-Mg-Si alloys containing different amounts of iron from 0.1 mass % to 0.7 mass %. The specimen continuously emitted a high amount of hydrogen when the stirrer started to rotate. This suggests that hydrogen was generated by a chemical reaction caused by the friction between the alloy surface and water. In addition, the pH value of the water dur...

Watch this Scientific Journal Video about Hydrogen Charging of Aluminum using Friction in Water at JoVE.com

Hydrogen Charging of Aluminum using Friction in Water

In order to introduce high amounts of hydrogen in aluminum and aluminum alloys, a new method of hydrogen charging was developed, called the friction in water procedure.

A new method of hydrogen charging of aluminum was developed by means of a friction in water (FW) procedure. This procedure can easily introduce high ...

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5.9K Views.  Osaka University. In order to introduce high amounts of hydrogen in aluminum and aluminum alloys, a new method of hydrogen charging was developed, called the friction in water procedure.

Video: Hydrogen Charging of Aluminum using Friction in Water

Controlling the Size, Shape and Stability of Supramolecular Polymers in Water

For aqueous based supramolecular polymers, the simultaneous control over shape, size and stability is very difficult1. At the same time, the ability to do so is highly important in view of a number of applications in functional soft matter including electronics, biomedical engineering, and sensors. In the past, successful strategies to control the size and shape of supramolecular polymers typically focused on the use of templates2,3, end cappers4 or selective solvent techniques5. 
Here we disclose a strategy based on self-assembling discotic amphiphiles that leads to the control over stack length and shape of ordered, chiral columnar aggregates. By balancing electrostatic repulsive interactions on the hydrophilic rim and attractive non-covalent forces within the hydrophobic core of the polymerizing building block, we manage to create small and discrete spherical objects6,7. Increasing the salt concentration to screen the charges induces a sphere-to-rod transition. Intriguingly, this transition is expressed in an increase of cooperativity in the temperature-dependent self-assembly mechanism, and more stable aggregates are obtained. 
For our study we select a benzene-1,3,5-tricarboxamide (BTA) core connected to a hydrophilic metal chelate via a hydrophobic, fluorinated L-phenylalanine based spacer (Scheme 1). The metal chelate selected is a Gd(III)-DTPA complex that contains two overall remaining charges per complex and necessarily two counter ions. The one-dimensional growth of the aggregate is directed by &pi;-&pi; stacking and intermolecular hydrogen bonding. However, the electrostatic, repulsive forces that arise from the charges on the Gd(III)-DTPA complex start limiting the one-dimensional growth of the BTA-based discotic once a certain size is reached. At millimolar concentrations the formed aggregate has a spherical shape and a diameter of around 5 nm as inferred from 1H-NMR spectroscopy, small angle X-ray scattering, and cryogenic transmission electron microscopy (cryo-TEM). The strength of the electrostatic repulsive interactions between molecules can be reduced by increasing the salt concentration of the buffered solutions. This screening of the charges induces a transition from spherical aggregates into elongated rods with a length &gt; 25 nm. Cryo-TEM allows to visualise the changes in shape and size. In addition, CD spectroscopy permits to derive the mechanistic details of the self-assembly processes before and after the addition of salt. Importantly, the cooperativity -a key feature that dictates the physical properties of the produced supramolecular polymers- increases dramatically upon screening the electrostatic interactions. This increase in cooperativity results in a significant increase in the molecular weight of the formed supramolecular polymers in water.

The goal of this experiment is to determine and control the size, shape and stability of self-assembled discotic amphiphiles in water. For aqueous based supramolecular polymers such level of control is very difficult. We apply a strategy using both repulsive and attractive interactions. The experimental techniques applied to characterize this system are broadly applicable.

For aqueous based supramolecular polymers, the simultaneous control over shape, size and stability is very difficult1. At the same time, the ability to do ...

The Preparation of Electrohydrodynamic Bridges from Polar Dielectric Liquids

Horizontal and vertical liquid bridges are simple and powerful tools for exploring the interaction of high intensity electric fields (8-20 kV/cm) and polar dielectric liquids. These bridges are unique from capillary bridges in that they exhibit extensibility beyond a few millimeters, have complex bi-directional mass transfer patterns, and emit non-Planck infrared radiation. A number of common solvents can form such bridges as well as low conductivity solutions and colloidal suspensions. The macroscopic behavior is governed by electrohydrodynamics and provides a means of studying fluid flow phenomena without the presence of rigid walls. Prior to the onset of a liquid bridge several important phenomena can be observed including advancing meniscus height (electrowetting), bulk fluid circulation (the Sumoto effect), and the ejection of charged droplets (electrospray). The interaction between surface, polarization, and displacement forces can be directly examined by varying applied voltage and bridge length. The electric field, assisted by gravity, stabilizes the liquid bridge against Rayleigh-Plateau instabilities. Construction of basic apparatus for both vertical and horizontal orientation along with operational examples, including thermographic images, for three liquids (e.g., water, DMSO, and glycerol) is presented.

Horizontal and vertical electrohydrodynamic liquid bridges are simple and powerful tools for exploring the interaction of high intensity electric fields and polar dielectric liquids. The construction of basic apparatus and operational examples, including thermographic images, for three liquids (e.g., water, DMSO, and glycerol) is presented.

Horizontal and vertical liquid bridges are simple and powerful tools for exploring the interaction of high intensity electric fields (8-20 kV/cm) and ...

Preparation and Friction Force Microscopy Measurements of Immiscible, Opposing Polymer Brushes

Solvated polymer brushes are well known to lubricate high-pressure contacts, because they can sustain a positive normal load while maintaining low friction at the interface. Nevertheless, these systems can be sensitive to wear due to interdigitation of the opposing brushes. In a recent publication, we have shown via molecular dynamics simulations and atomic force microscopy experiments, that using an immiscible polymer brush system terminating the substrate and the slider surfaces, respectively, can eliminate such interdigitation. As a consequence, wear in the contacts is reduced. Moreover, the friction force is two orders of magnitude lower compared to traditional miscible polymer brush systems. This newly proposed system therefore holds great potential for application in industry. Here, the methodology to construct an immiscible polymer brush system of two different brushes each solvated by their own preferred solvent is presented. The procedure how to graft poly(N-isopropylacrylamide) (PNIPAM) from a flat surface and poly(methyl methacrylate) (PMMA) from an atomic force microscopy (AFM) colloidal probe is described. PNIPAM is solvated in water and PMMA in acetophenone. Via friction force AFM measurements, it is shown that the friction for this system is indeed reduced by two orders of magnitude compared to the miscible system of PMMA on PMMA solvated in acetophenone.

The methodology to perform friction force microscopy experiments for contacting brushes is presented: Two polymer brushes that are grafted from (a) substrates and (b) colloidal probes are slid to show that, by using two contacting immiscible brush systems, friction in sliding contacts is reduced compared to miscible brush systems.

Solvated polymer brushes are well known to lubricate high-pressure contacts, because they can sustain a positive normal load while maintaining low ...

Reaction Kinetics and Combustion Dynamics of I4O9 and Aluminum Mixtures

Tetraiodine nonoxide (I4O9) has been synthesized using a dry approach that combines elemental oxygen and iodine without the introduction of hydrated species. The synthesis approach inhibits the topochemical effect promoting rapid hydration when exposed to the relative humidity of ambient air. This stable, amorphous, nano-particle material was analyzed using differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA) and showed an exothermic energy release at low temperature (i.e., 180 &#176;C) for the transformation of I4O9 into I2O5. This additional exothermic energy release contributes to an increase in overall reactivity of I4O9 when dry mixed with nano-aluminum (Al) powder, resulting in a minimum of 150% increase in flame speed compared to Al + I2O5. This study shows that as an oxidizer, I4O9 has more reactive potential than other forms of iodine(V) oxide when combined with Al, especially if I4O9 can be passivated to inhibit absorption of water from its surrounding environment.

Reaction Kinetics and Combustion Dynamics of I4O9 and Aluminum Mixtures

A protocol for measuring flame speeds of a reactive mixture composed of tetraiodine nonoxide (I4O9) and aluminum (Al) is presented. A method for resolving reaction kinetics using differential scanning calorimetry (DSC) is also presented. It was found that I4O9 is 150% more reactive than other iodine(V) oxides.

Tetraiodine nonoxide (I4O9) has been synthesized using a dry approach that combines elemental oxygen and iodine without the introduction of hydrated ...

Experimental Procedure for Warm Spinning of Cast Aluminum Components

High performance, cast aluminum automotive wheels are increasingly being incrementally formed via flow forming/metal spinning at elevated temperatures to improve material properties. With a wide array of processing parameters which can affect both the shape attained and resulting material properties, this type of processing is notoriously difficult to commission. A simplified, light-duty version of the process has been designed and implemented for full-size automotive wheels. The apparatus is intended to assist in understanding the deformation mechanisms and the material response to this type of processing. An experimental protocol has been developed to prepare for, and subsequently perform forming trials and is described for as-cast A356 wheel blanks. The thermal profile attained, along with instrumentation details are provided. Similitude with full-scale forming operations which impart significantly more deformation at faster rates is discussed.

An experimental protocol for instrumented warm rotary forming of cast aluminum alloys employing a bespoke industrially scaled apparatus is presented. Experimental considerations including thermal and mechanical effects are discussed, as well as similitude with full-scale processing of automotive wheels.

High performance, cast aluminum automotive wheels are increasingly being incrementally formed via flow forming/metal spinning at elevated temperatures to ...

Detecting the Water-soluble Chloride Distribution of Cement Paste in a High-precision Way

To improve the accuracy of the chloride distribution along the depth of cement paste under cyclic wet-dry conditions, a new method is proposed to obtain a high-precision chloride profile. Firstly, paste specimens are molded, cured, and exposed to cyclic wet-dry conditions. Then, powder samples at different specimen depths are grinded when the exposure age is reached. Finally, the water-soluble chloride content is detected using a silver nitrate titration method, and chloride profiles are plotted. The key to improving the accuracy of the chloride distribution along the depth is to exclude the error in the powderization, which is the most critical step for testing the distribution of chloride. Based on the above concept, the grinding method in this protocol can be used to grind powder samples automatically layer by layer from the surface inward, and it should be noted that a very thin grinding thickness (less than 0.5 mm) with a minimum error less than 0.04 mm can be obtained. The chloride profile obtained by this method better reflects the chloride distribution in specimens, which helps researchers to capture the distribution features that are often overlooked. Furthermore, this method can be applied to studies in the field of cement-based materials, which require high chloride distribution accuracy.

A protocol for obtaining a water-soluble chloride profile by using a high precision milling method is presented.

To improve the accuracy of the chloride distribution along the depth of cement paste under cyclic wet-dry conditions, a new method is proposed to obtain a ...

Simultaneous Multi-surface Anodizations and Stair-like Reverse Biases Detachment of Anodic Aluminum Oxides in Sulfuric and Oxalic Acid Electrolyte

After reporting on the two-step anodization, nanoporous anodic aluminum oxides (AAOs) have been widely utilized in the versatile fields of fundamental sciences and industrial applications owing to their periodic arrangement of nanopores with relatively high aspect ratio. However, the techniques reported so far, which could be only valid for mono-surface anodization, show critical disadvantages, i.e., time-consuming as well as complicated procedures, requiring toxic chemicals, and wasting valuable natural resources. In this paper, we demonstrate a facile, efficient, and environmentally clean method to fabricate nanoporous AAOs in sulfuric and oxalic acid electrolytes, which can overcome the limitations that result from conventional AAO fabricating methods. First, plural AAOs are produced at one time through simultaneous multi-surfaces anodization (SMSA), indicating mass-producibility of the AAOs with comparable qualities. Second, those AAOs can be separated from the aluminum (Al) substrate by applying stair-like reverse biases (SRBs) in the same electrolyte used for the SMSAs, implying simplicity and green technological characteristics. Finally, a unit sequence consisting of the SMSAs sequentially combined with SRBs-based detachment can be applied repeatedly to the same Al substrate, which reinforces the advantages of this strategy and also guarantees the efficient usage of natural resources.

A protocol for fabricating nanoporous anodic aluminum oxides via simultaneous multi-surfaces anodization followed by stair-like reverse biases detachments is presented. It can be applied repeatedly to the same aluminum substrate, exhibiting a facile, high-yield, and environmentally clean strategy.

After reporting on the two-step anodization, nanoporous anodic aluminum oxides (AAOs) have been widely utilized in the versatile fields of fundamental ...

In Situ High Pressure Hydrogen Tribological Testing of Common Polymer Materials Used in the Hydrogen Delivery Infrastructure

High pressure hydrogen gas is known to adversely affect metallic components of compressors, valves, hoses, and actuators. However, relatively little is known about the effects of high pressure hydrogen on the polymer sealing and barrier materials also found within these components. More study is required in order to determine the compatibility of common polymer materials found in the components of the hydrogen fuel delivery infrastructure with high pressure hydrogen. As a result, it is important to consider the changes in physical properties such as friction and wear in situ while the polymer is exposed to high pressure hydrogen. In this protocol, we present a method for testing the friction and wear properties of ethylene propylene diene monomer (EPDM) elastomer samples in a 28 MPa high pressure hydrogen environment using a custom-built in situ pin-on-flat linear reciprocating tribometer. Representative results from this testing are presented which indicate that the coefficient of friction between the EPDM sample coupon and steel counter surface is increased in high pressure hydrogen as compared to the coefficient of friction similarly measured in ambient air.

In Situ High Pressure Hydrogen Tribological Testing of Common Polymer Materials Used in the Hydrogen Delivery Infrastructure

A test methodology for quantifying tribological properties of polymers used in hydrogen infrastructure service is demonstrated and characteristic results for a common elastomer are discussed.

High pressure hydrogen gas is known to adversely affect metallic components of compressors, valves, hoses, and actuators. However, relatively little is ...

Design and Fabrication of an Optical Fiber Made of Water

In this report, an optical fiber of which the core is made solely of water, while the cladding is air, is designed and manufactured. In contrast with solid-cladding devices, capillary oscillations are not restricted, allowing the fiber walls to move and vibrate. The fiber is constructed by a high direct current (DC) voltage of several thousand volts (kV) between two water reservoirs that creates a floating water thread, known as a water bridge. Through the choice of micropipettes, it is possible to control the maximal diameter and length of the fiber. Optical fiber couplers, at both sides of the bridge, activate it as an optical waveguide, allowing researchers to monitor the water fiber capillary body waves through transmission modulation and, therefore, deducing changes in surface tension.
Co-confining two important wave types, capillary and electromagnetic, opens a new path of research in the interactions between light and liquid-wall devices. Water-walled microdevices are a million times softer than their solid counterparts, accordingly improving the response to minute forces.

This protocol describes the design and manufacture of a water bridge and its activation as a water fiber. The experiment demonstrates that capillary resonances of the water fiber modulate its optical transmission.

In this report, an optical fiber of which the core is made solely of water, while the cladding is air, is designed and manufactured. In contrast with ...

Determining Tribocorrosion Rate and Wear-Corrosion Synergy of Bulk and Thin Film Aluminum Alloys

The increasing complexity and severity of service conditions in areas, such as aerospace and marine industries, nuclear systems, microelectronics, batteries, and biomedical devices, etc., impose great challenges on the reliable performance of alloys exposed to extreme conditions where mechanical and electrochemical attack co-exist. Finding ways for alloys to mitigate the combined attack of wear and corrosion (i.e., tribocorrosion) under such extreme conditions is thus highly critical for improving their reliability and service lifetime when used in such conditions. The challenge lies in the fact that wear and corrosion are not independent of each other, but rather work synergistically to accelerate the total material loss. Thus, a reliable method to evaluate the tribocorrosion resistance of metals and alloys is needed. Here, a protocol for measuring the tribocorrosion rate and wear-corrosion synergy of Al-based bulk and thin film samples in a corrosive environment under room temperature is presented.

Here, we present a protocol to measure the tribocorrosion rate and wear-corrosion synergy of thin film and bulk Al alloys in simulated sea water at room temperature.

Hydrogen Charging of Aluminum using Friction in Water

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Controlling the Size, Shape and Stability of Supramolecular Polymers in Water

The Preparation of Electrohydrodynamic Bridges from Polar Dielectric Liquids

Preparation and Friction Force Microscopy Measurements of Immiscible, Opposing Polymer Brushes

Reaction Kinetics and Combustion Dynamics of I₄O₉and Aluminum Mixtures

Experimental Procedure for Warm Spinning of Cast Aluminum Components

Detecting the Water-soluble Chloride Distribution of Cement Paste in a High-precision Way

Simultaneous Multi-surface Anodizations and Stair-like Reverse Biases Detachment of Anodic Aluminum Oxides in Sulfuric and Oxalic Acid Electrolyte

In Situ High Pressure Hydrogen Tribological Testing of Common Polymer Materials Used in the Hydrogen Delivery Infrastructure

Design and Fabrication of an Optical Fiber Made of Water

Determining Tribocorrosion Rate and Wear-Corrosion Synergy of Bulk and Thin Film Aluminum Alloys