<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"></head><body style="overflow-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;"><div style="font-family: HelveticaNeue;"><font face="HelveticaNeue">Dear Soft Matter & Complex Systems Colleagues and Friends,</font></div><div><div style="font-family: HelveticaNeue;"><font face="HelveticaNeue"><br></font></div><div style="font-family: HelveticaNeue;"><font face="HelveticaNeue">On Friday 17 January 2025 at 9:30 AM at the UW Faculty of Physics (Pasteura 5, Warsaw; room 1.40) we are hosting a seminar during which </font></div><div style="font-family: HelveticaNeue;"><font face="HelveticaNeue"><br></font></div><div style="font-family: HelveticaNeue; margin: 0px; font-stretch: normal; line-height: normal; min-height: 14px;"><font face="HelveticaNeue"><b>Tomasz Bobiński</b></font><font face="HelveticaNeue"><b> </b></font><font face="HelveticaNeue">(</font><font face="HelveticaNeue">MEiL PW)</font></div><div style="font-family: HelveticaNeue; margin: 0px; font-stretch: normal; line-height: normal; min-height: 14px;"><font face="HelveticaNeue"><br></font></div><div style="font-family: HelveticaNeue; margin: 0px; font-stretch: normal; line-height: normal;"><font face="HelveticaNeue">will give a talk</font></div><div style="margin: 0px; font-stretch: normal; line-height: normal; min-height: 14px;"><div><h2 style="margin: 6px 0px 12px; padding: 0px;"><font face="HelveticaNeue"><span style="font-size: 12px;">Cloaking defects in a water waveguide system</span></font></h2><h2 style="font-family: HelveticaNeue; margin: 6px 0px 12px; padding: 0px;"><b style="caret-color: rgb(68, 68, 68);"><font face="HelveticaNeue" style="font-size: 12px;">Abstract</font></b></h2></div><div><div><font face="HelveticaNeue">Controlling surface water wave propagation is crucial for wave manipulation and cloaking technologies. By leveraging the invariance of shallow water equations under coordinate transformations, objects can be rendered invisible to incident waves. Traditional transformations often require spatially anisotropic bathymetries, which typically violate the assumptions of the depth-averaged models describing the propagation of water waves. We demonstrate that conformal mapping, which provides smoothly varying bathymetry, can be effectively applied to water waveguide systems with defects in the form of local variations in the waveguide wall shape. Our approach successfully cloaks these defects across a broad range of frequencies, including regimes where dispersive effects are significant. Despite the inherent dispersive nature of water waves, forward scattering remains weak, ensuring robust cloaking performance. Experimental results validate the broadband capabilities of this method.</font></div><div><font face="HelveticaNeue"><br></font></div><div><font face="HelveticaNeue">Based on the results obtained in the case of the meandering waveguide, we present a novel technique to render objects invisible to incident waves in a water waveguide system with parallel walls at low frequencies. The invisibility of a waveguide defect, specifically a vertical surface-piercing circular cylinder, is achieved through local deformations of the waveguide walls in the immediate vicinity of the defect. Our method results in a reflection coefficient that is at least 20 times lower than in the case of a parallel waveguide. The effect is observed over a broad frequency range. Experimental results confirm the high efficiency of our approach, showing that backscattered energy is reduced by a factor of 100 to 5000 compared to the reference case within the considered frequency range.</font></div></div><div style="font-family: HelveticaNeue;"><br></div></div><div style="font-family: HelveticaNeue; margin: 0px; font-stretch: normal; line-height: normal;"><font face="HelveticaNeue">We warmly welcome everyone to attend the talk and the Soft Matter Coffee Break after the seminar, held in room 2.63 (2nd floor).</font></div></div><div style="font-family: HelveticaNeue;"><font face="HelveticaNeue"><br></font></div><div style="font-family: HelveticaNeue;"><div dir="auto" style="overflow-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;"><div style="margin: 0px; font-stretch: normal; line-height: normal;"><font face="HelveticaNeue">Maria Ekiel-Jeżewska</font></div><div style="margin: 0px; font-stretch: normal; line-height: normal;"><font face="HelveticaNeue">Maciej Lisicki</font></div><div style="margin: 0px; font-stretch: normal; line-height: normal;"><font face="HelveticaNeue">Piotr Szymczak</font></div><div style="margin: 0px; font-stretch: normal; line-height: normal;"><font face="HelveticaNeue">Panagiotis Theodorakis</font></div><div style="margin: 0px; font-stretch: normal; line-height: normal;"><font face="HelveticaNeue">Marek Trippenbach</font></div></div></div></body></html>