Typed states for the displayed outbound observations.
Source: paper_references, paper_reference_links, observed 2026-08-04T20:45:37.739082Z
Paper Citation Record · LEDGER
As of 21 August 2026, this Paper Citation Record lists 68 of 68 outbound references and 0 inbound Pith citation observations for arXiv:2509.08378.
A citation records a reference. It does not transfer a finding from one paper to another.
Typed states for the displayed outbound observations.
Source: paper_references, paper_reference_links, observed 2026-08-04T20:45:37.739082Z
One-hop event checks from named stored sources.
Source: scholarly_work_events, retraction_status_cache, observed 2026-08-21T06:32:19.484+00:00
Pith citing papers itemized under the disclosed page cap.
Source: paper_references, paper_reference_links
A source-named dated measurement, never combined with another source.
Source: cited_works
68 of 68 outbound references displayed
External citation measurements
No source-named external measurement is stored.
Observation a0f7522b-9d4f-4b4f-85e3-50484b899564 · outbound
A Planning Strategy for Building a Heterogeneous Smart EM Environment 6G wireless systems: vision, requirements, challenges, insights, and opportunities,
Reference 1
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-21T06:32:19.484+00:00.
Observation 915016b8-8883-4351-aeb0-a0ad268e2f19 · outbound
A Planning Strategy for Building a Heterogeneous Smart EM Environment The roa d towards 6G: a comprehen- sive survey,
Reference 2
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-21T06:32:19.484+00:00.
Observation f6011ac7-5811-426d-b118-4fddfec07d5b · outbound
A Planning Strategy for Building a Heterogeneous Smart EM Environment GCWCN: 6G-based global coverage wireless communication network architecture,
Reference 3
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-21T06:32:19.484+00:00.
Observation c764252e-3a15-49fb-ac2c-18ff6fdf19d9 · outbound
A Planning Strategy for Building a Heterogeneous Smart EM Environment 5 G network planning under service and EMF constraints: Formulation and solutions,
Reference 4
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-21T06:32:19.484+00:00.
Observation 753a8c4f-35b0-4c6c-b147-9afb9de7cc2b · outbound
A Planning Strategy for Building a Heterogeneous Smart EM Environment Quality-of- experience evaluation for digital twins in 6G network envir onments,
Reference 5
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-21T06:32:19.484+00:00.
Observation 3b2ca3b0-ca51-4c22-a195-98b824506cb0 · outbound
A Planning Strategy for Building a Heterogeneous Smart EM Environment From digital twin to metaverse: the role of 6G ultrareliabl e and low-latency communi- cations with multi-tier computing,
Reference 6
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-21T06:32:19.484+00:00.
Observation e8c4f6f0-775c-4738-8fa0-db89737a84d9 · outbound
A Planning Strategy for Building a Heterogeneous Smart EM Environment Digital twin-aided orchestration of mobile ed ge computing with grant-free ac- cess,
Reference 7
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-21T06:32:19.484+00:00.
Observation 7ce5f073-3ab5-4ec3-85c5-7ea66b432eb9 · outbound
A Planning Strategy for Building a Heterogeneous Smart EM Environment Design of energy- and cost-efficient massive MIMO arrays,
Reference 8
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-21T06:32:19.484+00:00.
Observation 95b7e5da-0057-4843-b944-19ddfab7009f · outbound
A Planning Strategy for Building a Heterogeneous Smart EM Environment Designing smart electromagnetic environment s for next-generation wireless communications,
Reference 9
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-21T06:32:19.484+00:00.
Observation cff2e882-505e-47ed-a333-90e1411e4ade · outbound
A Planning Strategy for Building a Heterogeneous Smart EM Environment Smart radio environments empowered by reconfig urable intelligent surfaces: How it works, state of research, and the road ahead,
Reference 10
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-21T06:32:19.484+00:00.
Observation 6b1a98d9-0426-4f0a-9418-eee82d0d4756 · outbound
A Planning Strategy for Building a Heterogeneous Smart EM Environment Towards a heterogeneous smart electromagnetic envir onment for millimeter-wave communications: an industrial viewpoint,
Reference 11
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-21T06:32:19.484+00:00.
Observation 8755ee6c-79a8-4e53-98ba-d8caf5fa2a2e · outbound
A Planning Strategy for Building a Heterogeneous Smart EM Environment Guest Editorial Sma rt Electromagnetic Environ- ment,
Reference 12
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-21T06:32:19.484+00:00.
Observation eb0e4d0f-9b62-4f24-8049-27ddcc330d8d · outbound
A Planning Strategy for Building a Heterogeneous Smart EM Environment A path to smart rad io environments: an industrial viewpoint on reconfigurable intelligent surfac es,
Reference 13
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-21T06:32:19.484+00:00.
Observation 0af2cceb-9d6b-4902-95cd-8c7dfca3703a · outbound
A Planning Strategy for Building a Heterogeneous Smart EM Environment Hologra phic smart EM skins for ad- vanced beam power shaping in next generation wireless envir onments,
Reference 14
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-21T06:32:19.484+00:00.
Observation f25060d0-161c-474e-86dd-f9b5e95b3220 · outbound
A Planning Strategy for Building a Heterogeneous Smart EM Environment Macroscopic modeli ng of anomalously reflecting metasurfaces: angular response and far-field scattering,
Reference 15
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-21T06:32:19.484+00:00.
Observation 41310b3d-8c75-40e4-a54b-777d11efae40 · outbound
A Planning Strategy for Building a Heterogeneous Smart EM Environment Building a smart EM envi- ronment - AI-enhanced aperiodic micro-scale design of pass ive EM skins,
Reference 16
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-21T06:32:19.484+00:00.
Observation 8ded6fbd-d515-47cb-88da-09b3e5c828ab · outbound
A Planning Strategy for Building a Heterogeneous Smart EM Environment Constrained design of passive static EM skins,
Reference 17
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-21T06:32:19.484+00:00.
Observation a6087743-0c6d-47da-a4fb-743062f87254 · outbound
A Planning Strategy for Building a Heterogeneous Smart EM Environment On the design of modular reflecting EM skins for enhanced urban w ireless coverage,
Reference 18
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-21T06:32:19.484+00:00.
Observation 734fcb54-3fca-4c2e-820e-dad422ef76ad · outbound
A Planning Strategy for Building a Heterogeneous Smart EM Environment Perfect no n-specular reflection with polar- ization control by using a locally passive metasurface shee t on a grounded dielectric slab,
Reference 19
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-21T06:32:19.484+00:00.
Observation 76b00fc7-6e1d-41f3-843d-89e49bd8da9d · outbound
A Planning Strategy for Building a Heterogeneous Smart EM Environment Low-profile and low-visual impact smart electromagnetic curved passive sk ins for enhancing connectivity in urban scenarios,
Reference 20
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-21T06:32:19.484+00:00.
Observation fe258b90-d412-4f6c-949a-11f8ba99ae00 · outbound
A Planning Strategy for Building a Heterogeneous Smart EM Environment Reradiation and scattering from a reconfigurable intelligent surface: a gen eral macroscopic model,
Reference 21
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-21T06:32:19.484+00:00.
Observation 9ee78ef7-33ac-4685-9847-4e78e8c3051b · outbound
A Planning Strategy for Building a Heterogeneous Smart EM Environment An angle-insensitive 3-bit reconfigurable intelligent surfa ce,
Reference 22
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-21T06:32:19.484+00:00.
Observation 49ef9e72-2ae2-44a5-9577-daa2820afa77 · outbound
A Planning Strategy for Building a Heterogeneous Smart EM Environment On the study of reconfigurable intelligent surfaces in the near-field region,
Reference 23
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-21T06:32:19.484+00:00.
Observation bec25c89-dc6a-4e65-8c66-d4709f812a51 · outbound
A Planning Strategy for Building a Heterogeneous Smart EM Environment Macromodeling of reconfigurable intelligent surface based on microwave network theory,
Reference 24
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-21T06:32:19.484+00:00.
Observation 57d8f10e-d03a-4c53-97a4-8d3b1b0af657 · outbound
A Planning Strategy for Building a Heterogeneous Smart EM Environment Multi-scale single-bit RP- EMS synthesis for advanced propagation manipulation throu gh system-by-design,
Reference 25
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-21T06:32:19.484+00:00.
Observation a66b5049-812c-4303-952a-d3497b0cdaa0 · outbound
A Planning Strategy for Building a Heterogeneous Smart EM Environment Metasurfaces 3.0: a new paradigm f or enabling smart electro- magnetic environments,
Reference 27
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-21T06:32:19.484+00:00.
Observation 2a12779d-d9fa-4f2f-9337-722c66e051ac · outbound
A Planning Strategy for Building a Heterogeneous Smart EM Environment A statistical approa ch for robust metasurfaces and metasurface-based RIS engineering,
Reference 28
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-21T06:32:19.484+00:00.
Observation 10229554-8b89-43f7-a813-dba7b744ac1e · outbound
A Planning Strategy for Building a Heterogeneous Smart EM Environment Development of two-dimensional steerable reflectarray with liquid crystal for reconfigurable intelli gent surface applications,
Reference 29
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-21T06:32:19.484+00:00.
Observation 85e9649b-ecc1-4bf0-8250-290ce54a1cf4 · outbound
A Planning Strategy for Building a Heterogeneous Smart EM Environment Toward re al-world indoor smart electro- magnetic environments - A large-scale experimental demons tration,
Reference 30
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-21T06:32:19.484+00:00.
Observation 4dd5735f-5409-4caf-ab9c-92955b8883f5 · outbound
A Planning Strategy for Building a Heterogeneous Smart EM Environment Re- configurable intelligent surface (RIS) in the sub-6 GHz band : design, implementation, and real-world demonstration,
Reference 31
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-21T06:32:19.484+00:00.
Observation 27cf0727-ea6a-46a2-9de3-9955a79b336a · outbound
A Planning Strategy for Building a Heterogeneous Smart EM Environment Indoor coverage en- hancement for RIS-assisted communication systems: Practical measurements and efficient grouping,
Reference 32
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-21T06:32:19.484+00:00.
Observation 8fe2be77-81a0-4c1a-9082-59939f64d21d · outbound
A Planning Strategy for Building a Heterogeneous Smart EM Environment Experimental Evaluation of Multi-operator RIS-assisted Links in Indoor Environment
Reference 33
Source-reported events for the cited work
Unavailable: canonical work link unavailable.
Observation f490bcc2-dd5d-41a7-b169-ba66f2905bee · outbound
A Planning Strategy for Building a Heterogeneous Smart EM Environment High-resolution programmable scattering for wireless co verage enhancement: an indoor field trial campaign,
Reference 34
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-21T06:32:19.484+00:00.
Observation c1b7194b-416a-4f6c-80e8-7fb58434a30e · outbound
A Planning Strategy for Building a Heterogeneous Smart EM Environment Reconfigurable intelligent surfa ce-based wireless communi- cations: antenna design, prototyping, and experimental re sults,
Reference 35
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-21T06:32:19.484+00:00.
Observation 7ab857a8-0f41-49b2-b8c7-bc1d69256bdd · outbound
A Planning Strategy for Building a Heterogeneous Smart EM Environment RIS-Aided wireless communications: prototyping, adaptive beamform ing, and indoor/outdoor field trials,
Reference 36
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-21T06:32:19.484+00:00.
Observation 6632c32f-0974-4902-8a03-cd21b8a35fec · outbound
A Planning Strategy for Building a Heterogeneous Smart EM Environment Planning of EM skins for improved quality-of-service in urban areas,
Reference 37
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-21T06:32:19.484+00:00.
Observation 8f1e2138-034b-4296-8ade-5418efd60dab · outbound
A Planning Strategy for Building a Heterogeneous Smart EM Environment A multi-hop strategy for the planning of EM skins in a smart electromagnetic environm ent,
Reference 38
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-21T06:32:19.484+00:00.
Observation 01f3a50f-9693-4ae6-847a-5214c32f037c · outbound
A Planning Strategy for Building a Heterogeneous Smart EM Environment Coverage enhancement by deploying RIS in 5G commercial mobile networ ks: Field trials,
Reference 39
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-21T06:32:19.484+00:00.
Observation 74841eab-2005-49eb-adec-0c26c915eab3 · outbound
A Planning Strategy for Building a Heterogeneous Smart EM Environment Design and eva luation of reconfigurable intelligent surfaces in real-world environment,
Reference 40
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-21T06:32:19.484+00:00.
Observation 2e72f322-2609-490e-b705-1b96dc84bf62 · outbound
A Planning Strategy for Building a Heterogeneous Smart EM Environment Path loss modeling and measurements for reconfigurabl e intelligent surfaces in the 26 millimeter-wave frequency band,
Reference 41
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-21T06:32:19.484+00:00.
Observation 941931b1-f44c-46fe-b743-8ba1b9f4d9e4 · outbound
A Planning Strategy for Building a Heterogeneous Smart EM Environment A wideband rec onfigurable intelligent surface for 5G millimeter-wave applications,
Reference 42
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-21T06:32:19.484+00:00.
Observation c8c7f92d-5547-4b90-9404-761f6f3b31e8 · outbound
A Planning Strategy for Building a Heterogeneous Smart EM Environment Generalized anal ysis and unified design of EM skins,
Reference 43
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-21T06:32:19.484+00:00.
Observation 3baeb1ea-9d37-4677-8c21-1fb7fc8215a4 · outbound
A Planning Strategy for Building a Heterogeneous Smart EM Environment Active control of THz waves in wireless environments using graphene-based RI S,
Reference 44
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-21T06:32:19.484+00:00.
Observation 0ad1c0ea-00f1-4ef9-9654-5b7e38d9ee3e · outbound
A Planning Strategy for Building a Heterogeneous Smart EM Environment Computation-efficient refle ction coefficient design for graphene-based RIS in wireless communications,
Reference 45
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-21T06:32:19.484+00:00.
Observation 1697c55f-d388-4567-aeba-b38cc174dc51 · outbound
A Planning Strategy for Building a Heterogeneous Smart EM Environment Holis tic enlightening of blackspots with passive tailorable reflecting surfaces for efficient ur ban mmWave networks,
Reference 46
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-21T06:32:19.484+00:00.
Observation 09bba2ca-e965-4ba1-9192-58feb6b86cbb · outbound
A Planning Strategy for Building a Heterogeneous Smart EM Environment Lens based switched beam antenna for a 5G smart repeater,
Reference 47
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-21T06:32:19.484+00:00.
Observation 5fd3f3dc-69df-4f6a-af17-434fd99bf5b4 · outbound
A Planning Strategy for Building a Heterogeneous Smart EM Environment Network- controlled repeaters vs. reconfigurable intelligent surfa ces for 6G mmW coverage exten- sion: a simulative comparison,
Reference 48
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-21T06:32:19.484+00:00.
Observation 5bd51841-8afa-463e-a4f1-ae63575fc2a6 · outbound
A Planning Strategy for Building a Heterogeneous Smart EM Environment Metasurface coatin gs enabling antenna reconfig- urability for next-generation communications smart repea ters,
Reference 49
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-21T06:32:19.484+00:00.
Observation b97cf697-dfe5-4de7-aed0-cb225c147654 · outbound
A Planning Strategy for Building a Heterogeneous Smart EM Environment Shaping a smarter electromagnetic landscape: IAB, NCR, an d RIS in 5G standard and future 6G,
Reference 50
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-21T06:32:19.484+00:00.
Observation 26e5897c-85d0-45b6-a931-30654f81bb06 · outbound
A Planning Strategy for Building a Heterogeneous Smart EM Environment Spectrum and energy efficiencies for multiuser pairs massive MIMO systems with full-duplex amplify-and-f orward relay,
Reference 51
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-21T06:32:19.484+00:00.
Observation b8cdfe09-c2ab-4b6e-8760-902adef4b3ab · outbound
A Planning Strategy for Building a Heterogeneous Smart EM Environment On integrated access and backhaul networks: current statu s and potentials,
Reference 52
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-21T06:32:19.484+00:00.
Observation 33e3ec01-014f-436c-ad10-577d3f75e9b4 · outbound
A Planning Strategy for Building a Heterogeneous Smart EM Environment 5G; NR repeater radio transmission and receptio n,
Reference 53
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-21T06:32:19.484+00:00.
Observation 118fcb2b-7f96-40f1-82b2-ed7d762713d8 · outbound
A Planning Strategy for Building a Heterogeneous Smart EM Environment Routing and resource allocat ion for IAB multi-hop network in 5G advanced,
Reference 54
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-21T06:32:19.484+00:00.
Observation 796774a7-a991-49a9-98b4-05d7e730af4a · outbound
A Planning Strategy for Building a Heterogeneous Smart EM Environment 5G; NR integrated access and backhaul (IAB) radio transmiss ion and reception,
Reference 55
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-21T06:32:19.484+00:00.
Observation 03a05468-1534-4f01-aad9-4db68085611a · outbound
A Planning Strategy for Building a Heterogeneous Smart EM Environment Topology planning using Q-learning for microwave- based wireless backhaul networks,
Reference 56
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-21T06:32:19.484+00:00.
Observation 2c21b225-6a25-43f9-821f-9a1f2a71074c · outbound
A Planning Strategy for Building a Heterogeneous Smart EM Environment Boosting 5G mm-wave IAB reliability with reconfigurable intelligent surfaces,
Reference 57
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-21T06:32:19.484+00:00.
Observation c04d7251-5d95-4ecf-9eaf-bb201d81fb78 · outbound
A Planning Strategy for Building a Heterogeneous Smart EM Environment Towards reliable mmWave 6G RAN: Reconfigurable surfaces, smart repeaters, or both?,
Reference 58
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-21T06:32:19.484+00:00.
Observation 5851c034-5d7f-453c-8189-08450e525151 · outbound
A Planning Strategy for Building a Heterogeneous Smart EM Environment On antenna parameters self optimization in LTE cellular networks,
Reference 59
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-21T06:32:19.484+00:00.
Observation 6fd0a7ab-9cca-4149-a498-5fca19ebb092 · outbound
A Planning Strategy for Building a Heterogeneous Smart EM Environment Dynamic antenna azimuth pl anning for 3G, 4G and future 5G broadband radio networks
Reference 60
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-21T06:32:19.484+00:00.
Observation 6bcafbb8-1227-4ef8-ae0a-6a20c84e8419 · outbound
A Planning Strategy for Building a Heterogeneous Smart EM Environment A fast a nd elitist multiobjective genetic algorithm: NSGA-II,
Reference 61
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-21T06:32:19.484+00:00.
Observation 0871e1ef-a775-473b-ae0e-d4039be5872c · outbound
A Planning Strategy for Building a Heterogeneous Smart EM Environment No free lunch theorems for optimization,
Reference 62
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-21T06:32:19.484+00:00.
Observation b6a169b4-7282-466c-a088-9acb592f5bbd · outbound
A Planning Strategy for Building a Heterogeneous Smart EM Environment Accessed on: June 26, 2024
Reference 63
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-21T06:32:19.484+00:00.
Observation 417c454a-c7c0-44aa-9e4a-95cbcb402986 · outbound
A Planning Strategy for Building a Heterogeneous Smart EM Environment Unresolved cited work
Reference 64
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-21T06:32:19.484+00:00.
Observation 84c384d3-df49-4903-8d1f-d5d39cbef18e · outbound
A Planning Strategy for Building a Heterogeneous Smart EM Environment Unresolved cited work
Reference 65
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-21T06:32:19.484+00:00.
Observation 1a6ca978-8fa2-4a3e-b713-c5073f573210 · outbound
A Planning Strategy for Building a Heterogeneous Smart EM Environment ANSYS, Inc
Reference 66
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-21T06:32:19.484+00:00.
Observation 3b577ba0-289c-4664-9acc-1cc473f0e07e · outbound
A Planning Strategy for Building a Heterogeneous Smart EM Environment Accessed on: Jun
Reference 67
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-21T06:32:19.484+00:00.
Observation 9e6b9bf7-99e1-41f0-a080-070c57dd78f8 · outbound
A Planning Strategy for Building a Heterogeneous Smart EM Environment Integrated access and backhaul in 5G mmwave networks: potential and cha llenges,
Reference 68
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-21T06:32:19.484+00:00.
Observation 5f0d260b-88b2-4f3b-b841-37759df4812a · outbound
A Planning Strategy for Building a Heterogeneous Smart EM Environment Unfeasible Incident Angle
Reference 69
Source-reported events for the cited work
No event found in the named queried sources as of 2026-08-21T06:32:19.484+00:00.
No inbound Pith citation observations are available.